Permian marine deposits in Mongolia

The investigated stratigraphic section is situated within southeastern Mongolia (Fig. 1.1). Lithostratigraphic and sedimentological analyses revealed that Permian marine successions in Mongolia are stratigraphically partitioned into two discrete tectonostratigraphic belts (Manankov et al., Reference Manankov, Shi and Shu-zhong2006; Manankov, Reference Manankov2016; Afanasjeva and Manankov, Reference Afanasjeva, Manankov, Lopatin, Zelenkov and Parkhaev2019): the Central-Northeastern Belt and the Southeastern Belt (marked by the boundary between biogeographical provinces, see Fig. 1.2). These belts are organized as parallel NE-SW trending tectonic belts, demarcated by the South Mongolian microcontinent—a continental terrane characterized by nonmarine deposits (Manankov, Reference Manankov2016) (Fig. 1.2).

Figure 1.

Maps of Mongolia, showing study area (Hovsugol section) in southeastern Mongolia (1), and overall distribution map of Permian sedimentary rocks in Mongolia (2). The three numbered sections (black triangles in 2) are: 1 = the Adatzaq; 2 = the Tavan-Tolgoy sections; and 3 = the Binder (lkh-Uldsi Mountains). Base map modified from Manankov (Reference Manankov2016).

The Central-Northeastern Belt is exposed along a 900 km long NW-SW trending sublatitudinal belt in central and northeastern Mongolia. Its Permian succession consists of three stratigraphic horizons—the term ‘horizon’ here refers to an informal stratigraphic unit commonly used in Russian and Mongolian stratigraphic studies to denote rock bodies rather than interfaces (Manankov, Reference Manankov1998a, Reference Manankovb, Reference Manankov1999, Reference Manankov2004, Reference Manankov2012; Afanasjeva et al., Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003)—arranged in ascending order: Adaatsag, Tsagaantemet, and Binder (Manankov et al., Reference Manankov, Shi and Shu-zhong2006; Manankov, Reference Manankov2016) (Fig. 1.2).

The Adaatsag Horizon, represented by the Delgerkhangai Formation (Manankov, Reference Manankov2002), exceeds 1,000 m in thickness. The type section (Fig. 1.2, type section 1) is characterized by fine- to medium-grained terrigenous sedimentary rocks interbedded with coarse sandstone and conglomerate, with a volcanic and volcaniclastic base. This horizon yields brachiopods, including Jakutoproductus adatsagensis Pavlova, Reference Pavlova and Rozanov1988; Jakutoproductus ganelini Manankov, Reference Manankov2004; Lanipustula baicalensis Maslennikov, Reference Maslennikov and Markovskii1960; Anidanthus halinae Kotlyar, Reference Kotlyar and Sarytcheva1977; and Costatumulus sidorkini Manankov, Reference Manankov2004 (Manankov, Reference Manankov2002, Reference Manankov2004). Correlation with the brachiopod faunas from the Verkhoyansk Fold Belt (Kutygin, Reference Kutygin2006) and Transbaikalia (Kotlyar, et al., Reference Kotlyar, Kurilenko, Biakov, Popeko and Oleinikov2002) suggests an age of Sakmarian to early Artinskian (Manankov et al., Reference Manankov, Shi and Shu-zhong2006).

The Tsagaantemet Horizon, best represented in the lower to middle Ulz Formation, is divided into two members (Manankov, Reference Manankov2002). The lower member is typified by the Tavan-Tolgoy section (Fig. 1.2, type section 2) and mainly comprises sandstone and siltstone interbedded with limestone and conglomerate, include abundant brachiopods, bivalves, bryozoans, and plant fragments (Manankov, Reference Manankov2002). This horizon is assigned to the Roadian-Wordian (Manankov, Reference Manankov2002; Manankov et al., Reference Manankov, Shi and Shu-zhong2006).

The Binder Horizon, representing the upper Ulz Formation, is the youngest Permian marine unit in northern Mongolia and is restricted to a small northeastern area (Manankov et al., Reference Manankov, Shi and Shu-zhong2006) (Fig. 1.2). The type section, Ikh-Uldzi (Fig. 1.2, type section 3), comprises sandstone, calcareous siltstone, and interbedded limestone (Manankov et al., Reference Manankov, Shi and Shu-zhong2006). Brachiopods occur in limestone and calcareous siltstone (Manankov in Afanasjeva et al., Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003; Manankov, Reference Manankov2004), and the horizon is assigned to the Capitanian (Manankov et al., Reference Manankov, Shi and Shu-zhong2006).

According to Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991) and Manankov (Reference Manankov2016), the Southeastern Belt extends NE-SW for 800 km and includes several significant structural zones, i.e., the Solonker, Dalan-Uul-Lugin-Gol, Totoshan, and Hovsugol-Bairim-Ovoo zones. These zones hold keys in understanding the regional Permian stratigraphy. As a whole, the Permian deposits of this belt are divided into five horizons in ascending order: Agui-Uul, Totoshan, Hovsugol, Tsagaan-Uul, and Solonker (Manankov, Reference Manankov1998b, Reference Manankov1999, Reference Manankov2012; Manankov et al., Reference Manankov, Shi and Shu-zhong2006).

The Agui-Uul Horizon, the lowest marine unit, consists of sandstone, siltstone, and limestone in the Dalan-Uul-Lugin-Gol structural zone, and interbedded volcanic rocks, sandstone, and limestone in the Hovsugol-Bairim-Ovoo zone. Fossils mainly include foraminifers, associated with rare brachiopods, bryozoans, and corals. It is assigned to the Asselian, based on foraminiferal correlation with the South Urals (Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991; Manankov, Reference Manankov1998b; Manankov et al., Reference Manankov, Shi and Shu-zhong2006).

The Totoshan Horizon is the most widespread, occurring in the Hovsugol-Bairim-Ovoo, Totoshan, and Solonker structural zones. It consists mainly of volcanic rocks and sandstones, with local fossiliferous limestones and conglomerates, and is assigned to the Sakmarian-Artinskian (Manankov et al., Reference Manankov, Shi and Shu-zhong2006).

The Hovsugol Horizon includes the Kharnuden and Bulgan-Uul formations. It consists of calcareous sandstone, siltstone, thin-bedded calcareous mudstone, and conglomerate. Fossils are dominated by brachiopods, with bryozoans, bivalves, gastropods, and ammonoids, Manankov (Reference Manankov2016) suggested that the age of this horizon corresponds to a late Artinskian to Kungurian age, with the faunal assemblages exhibiting strong Boreal characteristics, as reflected in the dominance of cold-water taxa.

The Tsagaan-Uul Horizon, represented by the Lugin-Gol Formation, conformably underlies the Bulgan-Uul Formation in the Dalan-Uul-Lugin-Gol structural zone and the Tavankhar Formation in the Solonker structural zone (Fig. 1.2). It comprises sandstone, conglomerate, calcareous siltstone, and limestone, with increasing carbonate content in the upper section. Brachiopods are dominant, with several biostratigraphic zones established (Manankov, Reference Manankov1999; Manankov et al., Reference Manankov, Shi and Shu-zhong2006). Correlation with brachiopod zones from Transbaikalia, the Verkhoyansk Fold Belt, and the Kolyma-Omolon Basin suggests a Roadian-early Wordian age (Manankov, Reference Manankov1999; Manankov et al., Reference Manankov, Shi and Shu-zhong2006).

The Solonker Horizon is the uppermost marine unit in the Permian in southeastern Mongolia, occurring in the upper Lugin-Gol Formation of the Dalan-Uul-Lugin-Gol structural zone (Fig. 1.2). It consists of alternating limestone, calcareous mudstone, siltstone, and sandstone, with warm-water brachiopods dominating the fossil assemblage (Manankov, Reference Manankov1999; Afanasjeva et al., Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003). Correlation with brachiopod faunas from South Primorye (Kotlyar et al., Reference Kotlyar, Nikitina, Zhuravlev and Kossovaya2003) and Inner Mongolia, China, suggests a Capitanian age (Manankov et al., Reference Manankov, Shi and Shu-zhong2006; Shen et al., Reference Shen, Zhang, Shang and Li2006; Shi, Reference Shi2006).

Fossil localities

All specimens were collected from the Kharnuden Formation at the Hovsugol section in southeastern Mongolia, located 14 km east of a small village called Hovsugol (locally known as ‘somon Hovsugol,’ meaning ‘small village of Hovsugol’ in Mongolian). The section is exposed on both sides of a small hill in the southeastern Gobi Desert region (GPS: 43.62044°N, 109.82647°E). This locality forms part of the Hovsugol Horizon within the Hovsugol-Bairim-Ovoo structural zone and represents Permian marine deposits rich in marine fossils, primarily brachiopods, with occasional occurrences of bivalves, bryozoans, gastropods, conodonts, and ammonoids. The section comprises 20 lithological layers (beds; see Fig. 2) assigned to the Kharnuden Formation, with a total measured thickness of 108 m. The main body of the section consists of yellow-green calcareous siltstone, fine- to coarse-grained sandstone, and mudstone, with interspersed with occasional thin (0.1–0.3 m) and discontinuous sandy limestone layers, sometimes intercalated with limestone lenses. Several calcareous siltstone and sandy limestone beds (e.g., Hv-5, 7, 9, 14; see Fig. 2) are particularly rich in brachiopod fossils. Bivalves are locally abundant in the basal sandstone layers (Hv-3) and in mixed fossil assemblages (Hv-4). The grain size of the sandstone generally decreases upward, transitioning from coarse and calcareous sandstone at the base (Hv-1–4) to finer siltstone and mudstone toward the top. Further details of the lithological succession are presented in Figure 2.

Figure 2.

Stratigraphic sequence and fossil distribution of the Hovsugol section.

Materials

The total number of specimens collected exceeded 2,700, including ~ 1,480 ventral valves, 160 dorsal valves, 820 molds of both ventral and dorsal valves, 200 articulated shells and their internal molds, and additional specimens with the internal structures of both ventral and dorsal valves.

Methods

The most representative samples were photographed and illustrated. The suprageneric classification used in this study largely follows the second edition of the Treatise on Invertebrate Paleontology, Part H, Brachiopoda (revised), volumes 1–6 (Kaesler, Reference Kaesler2000, Reference Kaesler2002, Reference Kaesler2006; Selden, Reference Selden2007). In addition, data recorded in the Paleobiology Database (https://paleobiodb.org) were also consulted.

Repository and institutional abbreviation

All of the specimens described herein are housed in the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China, with formal registration numbers with a prefix NIGP.

Beishan area, Gansu Province, China

The marine Permian strata of the Beishan area in Gansu Province (including the Shuangbaotang, Jushitan, and Jinta formations) exhibit both similarities and differences compared to the Hovsugol Horizon of southeastern Mongolia in terms of brachiopod assemblages (Zhu, Reference Zhu1983).

The Shuangbaotang Formation in Beishan contains brachiopods like Yakovlevia mammatiformis Fredericks, Reference Fredericks1926; Waagenoconcha sp. indet.; Cancrinella koninckiana (Keyserling, Reference Keyserling, Von Krusenstern and Keyserling1846); Cancrinella cancriniformis Tschernyschew, Reference Tschernyschew1889; Cancrinella pseudotruncata (Ustritsky, Reference Ustritsky, Ustritsky, Hu and Chang1960); Linoproductus sp. indet.; Marginifera gobiensis Chao, Reference Chao1927; Echinauris jisuensis Chao, Reference Chao1927; Streptorhynchus sp. indet.; Spiriferella keilhaviformis Fredericks, Reference Fredericks1916; Spiriferella keilhavii (von Buch, Reference von Buch1847); Anidanthus sinuata Ustritsky, Reference Ustritsky, Ustritsky and Tschernjak1963b; Leptodus nobilis Waagen, Reference Waagen1883 in 1882–1885; Neospirifer fasciger (Keyserling, Reference Keyserling, Von Krusenstern and Keyserling1846); Stenoscisma purdoniformis Grabau, Reference Grabau1931; and Cleiothyridina subexpansa Waagen, Reference Waagen1883 in 1882–1885 (Ustritsky, Reference Ustritsky, Ustritsky, Chunfa, Qinglin, Jingzhi and Yunjie1963a; Ding and Qi, Reference Ding and Qi1983). Bu et al. (Reference Bu, Duan and Niu2011) also reported a diverse brachiopod fauna from the Shuangbaotang Formation at the Kalushan and Meiyao Xishan sections in Ejin Banner, western Inner Mongolia, including Derbyia Waagen, Reference Waagen1884 in 1882–1885; Yakovlevia Fredericks, Reference Fredericks1925; Waagenoconcha Chao, Reference Chao1927; Marginifera Waagen, Reference Waagen1884 in 1882–1885; Uraloproductus Ustritskiy, Reference Ustritsky1971; Paramarginifera Fredericks, Reference Fredericks1916; Linoproductus; Neospirifer Fredericks, Reference Fredericks1924; Spiriferella Tschernyschew, Reference Tschernyschew1902; Stenoscisma Conrad, Reference Conrad1839; Rhynchopora King, Reference King1865; and others, which show close similarity with the Hovsugol fauna described here. Most of these genera also occur in the Hovsugol Horizon, suggesting a close similarity in species composition between the two regions. Both formations are considered to be of late Artinskian to Roadian age (Liang, Reference Liang1981; Zhu, Reference Zhu1983; Bu et al., Reference Bu, Duan and Niu2011).

The Jushitan and Jinta formations, in contrast, exhibit greater regional differences, particularly in species composition and age (Zhu, Reference Zhu1983). According to the reports of the Regional Geological Survey Team in Gansu Bureau of Geology (1980, ‘Permian of Gansu Province,’ unpublished internal material), Ding and Qi (Reference Ding and Qi1983), Zhu (Reference Zhu1983) and the Bureau of Geology and Mineral Resources of Gansu Province (1989), brachiopods from the Jushitan Formation include Schuchertella sp. indet.; Neospirifer sp. indet.; Uncinunellina mongolica Grabau, Reference Grabau1931; Uncinunellina timorensis Beyrich, Reference Beyrich1865; Spiriferella saranae de Verneuil, Reference de Verneuil, Murchison, Verneuil and Keyserling1845; Permocryptospirifer omeishanensis Zhu, Reference Zhu1983; Tenuichonetes aff. T. tenuilirata Chao, Reference Chao1928; Marginifera typica Waagen, Reference Waagen1884 in 1882–1885; Marginifera morrisi Chao, Reference Chao1927; Streptorhynchus? kayseri Schellwien, Reference Schellwien1900; and Schellwienella crenistria McIntosh, Reference McIntosh1974, are more similar to those of the lower part of the Maokou Formation (Guadalupian) in South China. The Jinta Formation yields fewer marine fossils, although some brachiopods have been reported, including Obiculoidea sp. indet.; Phricodothyris asiatica Chao, Reference Chao1929; and Spiriferella rajah Salter in Salter and Blanford, Reference Salter and Blanford1865 (p. 59) (Regional Geological Survey Team of the Gansu Bureau of Geology, 1980, ‘Permian of Gansu Province,’ unpublished internal material; Zhu, Reference Zhu1983). Based on its stratigraphic relationship with the overlying Wordian-aged Jushitan Formation, the Jinta Formation is likely Capitanian in age.

Inner Mongolia, China

The brachiopod faunas of the Hovsugol region and Inner Mongolia’s Zhesi and Ekenalsileng areas share several common elements but also display notable differences.

In the Ekenalsileng area of Badain Jaran Desert, west of Inner Mongolia, the brachiopod fauna is estimated to be ~ 90% similar to that of the Shuangbaotang Formation in Beishan. This includes species like Acosarina indica Waagen, Reference Waagen1884 in 1882–1885; Schizophoria resupinata Martin, Reference Martin1809; Enteletes sp. indet.; Orthotetes sp. indet.; Schellwienella sp. indet.; Waagenoconcha cf. W. purdoni (Davidson, Reference Davidson1862); Juresania juresanensis Tschernyschew, Reference Tschernyschew1902; Anidanthus sinuata; Spinomarginifera sp. indet.; Dictyoclostus sp. indet.; Marginifera morrisi; Tyloplecta yangtzeensis Chao, Reference Chao1927; Liosotella spitzbergiana (Toula, Reference Toula1874); Yakovlevia cf. Y. mammata Keyserling, Reference Keyserling, Von Krusenstern and Keyserling1846; Yakovlevia cf. Y. mammatiformis; Cancrinella sp. indet.; Linoproductus? sp. indet.; Spiriferella saranae; Spiriferella salteri Tschernyschew, Reference Tschernyschew1902; Spiriferella persaranae Grabau, Reference Grabau1931; Neospirifer fasciger; Neospirifer cf. N. ravana; Crurithyris sp. indet.; Martinia sp. indet.; Dielasma sp. indet.; and Hustedia grandicosta Davidson, Reference Davidson1862 (Zhang, Reference Zhang1990). These species are also found in the Hovsugol and Tsagaan-Uul Horizons of southeastern Mongolia, supporting the idea that the Ekenalsileng fauna represents an eastern extension of the Hovsugol fauna.

In contrast, the Zhesi area of Inner Mongolia exhibits more regional variation. Although some species from the Zhesi Formation also occur in southeastern Mongolia—e.g., Yakovlevia mammatiformis; Waagenoconcha permocarbonica Ustritsky, Reference Ustritsky, Ustritsky and Tschernjak1963b; and Neospirifer ravana (Diener, Reference Diener1897)—the overall faunal composition is more distinct (Ding et al., Reference Ding, Xia, Duan, Li, Liu and Liang1985; Wang and Zhang, Reference Wang and Zhang2003). The Zhesi Formation is largely associated with the Tsagaan-Uul Horizon in Mongolia, with overlapping species between the two regions. The Zhesi brachiopod fauna reflects both Boreal and Tethyan affinities, with a predominance of Tethyan elements, and is dated to the Wordian (Leven et al., Reference Leven, Grunt, Lin and Li2001; Wang et al., Reference Wang, Wang and Li2006).

The overlying Yihewusu Formation contains brachiopods with a strong Paleotethyan influence, including Streptorhynchus sp. indet., Echinauris jisuensis, and Cancrinella koninckiana. These species are also found in both the Solonker Horizon of southeastern Mongolia and the Yihewusu Formation (Shi et al., Reference Shi, Archbold and Zhan1995). The Yihewusu Formation is considered to be of Capitanian age (Li and Duan, Reference Li and Duan1985; Leven et al., Reference Leven, Grunt, Lin and Li2001; Wang and Zhang, Reference Wang and Zhang2003; Shen et al., Reference Shen, Zhang, Shang and Li2006).

The Xiujimqinqi area also demonstrates strong faunal similarity with southeastern Mongolia, particularly in terms of species composition. Brachiopods from the Xiujimqinqi Formation include Kaninospirifer adpressum (Liu and Waterhouse, Reference Liu and Waterhouse1985); Yakovlevia mammatiformis; Spiriferella keilhavii; and Neospirifer sp. indet., overlapping with those found in the Zhesi and Yihewusu formations as well as in the Tsagaan-Uul and Solonker Horizons of southeastern Mongolia (Shi et al., Reference Shi, Shen and Tazawa2002a). These correlations point to similar environmental conditions and active faunal exchanges. The formation spans a Wordian to Capitanian age and displays a mixture of Boreal and Tethyan affinities, consistent with other Permian sequences in Mongolia.

South Primorye, Russian Far East

The Permian brachiopod faunas of South Primorye correlate with those of southeastern Mongolia and other regions of East Asia, highlighting both regional continuity and faunal interchange during the Permian (Chernysh and Kiseleva, Reference Chernysh and Kiseleva1971; Burago et al., Reference Burago, Kiseleva, Kotlyar, Nikitina, Sosnina, Taschi, Krasny and Popeko1974; Nikitina, Reference Nikitina, Kireeva and Ablaev1974; Licharew and Kotlyar, Reference Licharew, Kotlyar and Popeko1978; Kiseleva, Reference Kiseleva1982, Reference Kiseleva, Zakharov and Onoprienko1986; Zakharov and Pavlov, Reference Zakharov, Pavlov, Zakharov and Onoprienko1986; Kotlyar et al., Reference Kotlyar, Kropatcheva, Sosnina, Pronina, Chedija, Zakharov, Beljaeva and Nikitina1990, Reference Kotlyar, Nikitina, Zhuravlev and Kossovaya2003, Reference Kotlyar, Popeko and Kurilenko2006a; Khanchuk, Reference Khanchuk, Zakharov, Panchenko and Khanchuk1992; Belayeva et al., Reference Belayeva, Kiseleva, Nikitina, Baud, Popova, Dickins, Lucas and Zakharov1997; Zakharov et al., Reference Zakharov, Oleinikov, Kotlyar and Dickins1997, Reference Zakharov, Oleinikov, Kotlyar, Burago, Rudenko and Dorukhovskaya1999; Shi et al., Reference Shi, Lee, Kotlyar and Zakharov2022). However, the brachiopod fauna from the Pilnikov Formation (Kungurian) is represented by only four species, demonstrating a markedly impoverished composition despite sharing two key species (Ingelarella atlanicha and Primorewia reshetnikov) with the Hovsugol fauna from southeastern Mongolia (Shi et al., Reference Shi, Lee, Kotlyar and Zakharov2022).

The Permian strata in South Primorye are divided into five ascending horizons: Dunay, Abrek, Vladivostok, Chandalaz, and Lyudyanza. The Abrek Horizon comprises continental to shallow marine facies, with abundant plant fossils in the lower part and marine invertebrates, including brachiopods, in the middle part. Brachiopods like Rhynchopora variabilis Stuckenberg, Reference Stuckenberg1898; Rhynchopora nikitini Tschernyschew, Reference Tschernyschew1885; Rhynoleichus subglobosus Abramov and Grigorjewa, Reference Abramov and Grigorjewa1988; Primorewia reshetnikov; Fusispirifer cf. F. nitiensis Diener, Reference Diener1897; and Ingelarella atlanicha correlate with those from the Hovsugol Horizon of southeastern Mongolia (Zakharov et al., Reference Zakharov, Oleinikov, Kotlyar, Burago, Rudenko and Dorukhovskaya1999), indicating a Kungurian age (Kotlyar et al., Reference Kotlyar, Kossovaya, Shishlov, Zhuravlev and Pukhonto2004).

The Vladivostok Horizon, composed of volcanic and siliciclastic rocks, contains bryozoans, ammonoids, and brachiopods like Yakovlevia mammata; Waagenoconcha angustata Sarytcheva, Reference Sarytcheva1984; Liosotella decimana Manankov, Reference Manankov, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991; Rhynchopora tchernyshae Koczyrkevicz, Reference Koczyrkevicz and Gramm1979; Spiriferella keilhaviformis; Spiriferella salteri; Kaninospirifer adpressum; Kaninospirifer kaninensis Licharew, Reference Licharew1943; Kaninospirifer stepanovi Grunt, Reference Grunt and Grunt2006; Rhombospirifer zhesiensis Duan and Li, Reference Duan and Li1985; Blasispirifer reedi Licharew and Kotlyar, Reference Licharew, Kotlyar and Popeko1978; and Alispiriferella lita (Fredericks, Reference Fredericks1924). These species are associated with the Liosotella decimana-Waagenoconcha angustata assemblage of the Tsagaan-Uul Horizon in southeastern Mongolia (Kotlyar et al., Reference Kotlyar, Belyansky, Burago, Nikitina, Zakharov and Zhuravlev2006b). Ammonoid evidence suggests a Roadian to Wordian age (Zakharov and Pavlov, Reference Zakharov, Pavlov, Zakharov and Onoprienko1986; Kotlyar et al., Reference Kotlyar, Popeko and Kurilenko2006a).

The Chandalaz Horizon contains a diverse marine fauna, including fusulinids and brachiopods. The Leptodus nobilis-Spiriferella rajah assemblage, found there, is comparable to the Richthofenia cornuformis-Enteletes andrewsi Biozone of the Yihewusu Formation in the Zhesi area (Wang and Zhang, Reference Wang and Zhang2003) and the Echinauris jisuensis assemblage of the Solonker Horizon in southeastern Mongolia (Kotlyar et al., Reference Kotlyar, Nikitina, Zhuravlev and Kossovaya2003, Reference Kotlyar, Shen, Kossovaya and Zhuravlev2007). Ammonoid and conodont data indicate a Capitanian age for this horizon (Kotlyar et al., Reference Kotlyar, Popeko and Kurilenko2006a).

Japan

Permian deposits in Japan are distributed across a range of tectonic settings, including continental margins (e.g., the South Kitakami and Hida Gaien belts), seamounts (e.g., the Akiyoshi and Mino terranes), and continental slope to ocean trench settings (e.g., the Maizuru Belt). Among these, the South Kitakami and Hida Gaien belts are particularly informative for paleobiogeographic comparisons with southeastern Mongolia and the Hovsugol region.

The South Kitakami Belt is especially well known for its well-preserved Permian stratigraphy. The lower Permian Sakamotozawa Formation hosts a diverse brachiopod assemblage that includes Waagenoconcha humboldti d’Orbigny, Reference d’Orbigny1842; Orthotetes callytharrensis (Thomas, Reference Thomas1958); Rhynchopora sp. indet.; Streptorhynchus sp. indet.; Meekella mexicana Girty, Reference Girty1909; Chaoiella gruenewaldti Krotow, Reference Krotow1888; and Phricodothyris sp. indet. (Nakamura, Reference Nakamura1959; Tazawa, Reference Tazawa1974; Tazawa and Shintani, Reference Tazawa and Shintani2022). Although the taxonomic composition differs from that of the Hovsugol region, the presence of shared genera, e.g., Orthotetes Fischer de Waldheim, Reference Fischer de Waldheim1829; Streptorhynchus King, Reference King1850; and Phricodothyris George, Reference George1932, suggests a degree of faunal correlation, albeit with notable differences at the species level.

A diverse Tashiroyama brachiopod fauna, consisting of 11 species including Transennatia insculpta Grant, Reference Grant1976; Echinauris sp. indet.; Anidanthus sp. indet.; Dicystoconcha lapparenti Termier et al., Reference Termier, Termier, de Lapparent and Marin1974; Hustedia ratburiensis Waterhouse and Piyasin, Reference Waterhouse and Piyasin1970; Martinia lata Grabau, Reference Grabau1936; Jilinmartinia sp. indet.; and Martiniopsis sp. indet., was described from the base of the Kanokura Formation in the Nagaiwa-Sakamotozawa area, South Kitakami Belt, which is assigned to the Kungurian (Tazawa and Shitani, Reference Tazawa and Shintani2022). This fauna is similar to that described herein at the generic level, but most are unidentifiable to species level.

The Moribu Formation in the Hida Gaien Belt (Midian to Wordian) contains a rich brachiopod fauna, including Yakovlevia kaluzinensis Fredericks, Reference Fredericks1925; Waagenoconcha permocarbonica; Rhynchopora sp. indet.; Blasispirifer reedi; Alispiriferella lita; Neospirifer cf. N. fasciger; Cancrinella cf. C. spinosa (Hayasaka and Minato, Reference Hayasaka and Minato1956); Megousia sp. indet.; and Stenoscisma margaritovi Tschernyschew, Reference Tschernyschew1902 (Tazawa, Reference Tazawa2000, Reference Tazawa2001b). These assemblages also show close similarity to those from the upper Kanokura Series (Guadalupian) in the South Kitakami Belt, the Chandalaz Horizon in South Primorye, the Zhesi Formation in Inner Mongolia, and the upper Tsagaan-Uul Horizon in southeastern Mongolia. Shared species include Alispiriferella lita; Blasispirifer reedi; Leptodus nobilis; Linoproductus lineatus Waagen, Reference Waagen1884 in 1882–1885; Rhynchopora tscheryshae; Stenoscisma margaritovi; Transennatia gratiosa Waagen, Reference Waagen1884 in 1882–1885; and Yakovlevia kaluzinensis, highlighting a strong biogeographic connection between the Hida Gaien Belt and these regions.

Other areas of East Asia

The brachiopod fauna of the Hovsugol section in southeastern Mongolia markedly differs from that of the Transbaikal region, central-northeastern Mongolia, and the Khabarovsk region of the Russian Far East, which are characterized by typical Boreal faunas restricted to the Boreal Realm.

For example, the Permian (mainly Cisuralian–Guadalupian) brachiopods reported from Transbaikal include Jakutoproductus zabaikalicus Kotlyar et al., Reference Kotlyar, Kurilenko, Biakov, Popeko and Oleinikov2002; Anidanthus halinae; Anidanthus boikovi Stepanov, Reference Stepanov1946; Tomiopsis laevis Kotlyar et al., Reference Kotlyar, Kurilenko, Biakov, Popeko and Oleinikov2002; Costatumulus sidorkini; Olgerdia ganelini (Grigorjewa, Reference Grigorjewa1977); Olgerdia zavodowskii (Grigorjewa, Reference Grigorjewa1977); Rhynchopora lobjaensis Tolmatchew, Reference Tolmatchew1912; Terrakea sp. indet.; Magadania bajkurica Ustritsky, Reference Ustritsky, Ustritsky and Tschernjak1963b; Magadania modotonensis Kotlyar, Reference Kotlyar and Sarytcheva1977; Cancrinelloides obrutschewi Licharew, Reference Licharew1934; Cancrinelloides cf. C. curvatus Tolmatchew, Reference Tolmatchew1912; Cancrinelloides licharewi Kotlyar, Reference Kotlyar and Sarytcheva1977; Neospirifer subfasciger Licharew, Reference Licharew1934; Neospirifer cf. N. moosakhailensis (Davidson, Reference Davidson1862); Bajtugania boguchanica Solomina, Reference Solomina1988; Megousia zabaicalica Kotlyar et al., Reference Kotlyar, Kurilenko, Biakov, Popeko and Oleinikov2002; Cleiothyridina cf. C. nikolaevi Grunt, Reference Grunt and Sarycheva1977; Crassispirifer cf. C. monumentalis Abramov and Grigorjewa, Reference Abramov and Grigorjewa1988; Penzhinella micluchomanclayi Kotlyar et al., Reference Kotlyar, Kurilenko, Biakov, Popeko and Oleinikov2002; and Attenuatella olexivi Kotlyar et al., Reference Kotlyar, Kurilenko, Biakov, Popeko and Oleinikov2002. None of these is found in the Hovsugol fauna.

Similarly, the Permian faunas from central-northeastern Mongolia consist of Boreal-type brachiopods, e.g., Jakutoproductus adatsagensis; Jakutoproductus ganelini; Lanipustula baikalensis; Anidanthus halinae; Tomiopsis laevis; Costatumulus sidorkini; Mongolochonetes sp. indet.; Neospirifer kedonensis Einor in Kaschirzev, Reference Kaschirzev1959; Neospirifer invisus Zavodowsky, Reference Zavodowsky1958; Magadania modotonensis; Cancrinelloides obrutschewi; Cancrinelloides licharewi; Bajtugania duseevi Grunt, Reference Grunt1991; Kiangsiella sp. indet.; Orthotetes afanasjevae Manankov, Reference Manankov2004; Adatsagochonetes mongolicus Afanasjeva, Reference Afanasjeva2004; Brachythyrina sp. indet.; Mongousia spinea Manankov, Reference Manankov1992; Tumarinia ganelini Grigorjewa, Reference Grigorjewa, Ganelin, Kotlyar and Sarytcheva1977; and Tumarinia zavodowskyi Grigorjewa, Reference Grigorjewa1977 (Manankov, Reference Manankov2002, Reference Manankov2004, Reference Manankov2008, Reference Manankov2012; Afanasjeva et al., Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003).

Thus, the brachiopod assemblage from southeastern Mongolia shows minimal taxonomic overlap with those from the Transbaikal region, northeastern Mongolia, and Khabarovsk. In contrast, the latter regions exhibit substantial faunal similarity among themselves, sharing species like Anidanthus halinae, Tomiopsis laevis, Costatumulus sidorkini, Magadania modotonensis, Cancrinelloides obrutschewi, and Cancrinelloides licharewi, indicating that they belong to a Boreal-affinity faunal province (Kotlyar et al., Reference Kotlyar, Popeko and Kurilenko2006a; Shi, Reference Shi2006).

Overall, the brachiopod fauna from the Hovsugol section in southeastern Mongolia exhibits strong species-level affinities with those from the Beishan area in northwestern China, the Ekenalsileng area of the Badain Jaran Desert in western Inner Mongolia, the Zhesi and Xiujimqinqi areas in central and eastern Inner Mongolia, South Primorye in the Russian Far East, and the South Kitakami and Hida Gaien belts in Japan. In contrast, the Hovsugol assemblage is markedly distinct from the brachiopod faunas of the Transbaikal region, central-northeastern Mongolia, and the Verkhoyansk and Kolyma-Omolon regions of northeastern Russia.

Paleobiogeographical implications

Analysis of the paleobiogeographical distribution of Carboniferous and Permian brachiopod faunas in Mongolia indicates that the Mongolian sedimentary basins, from the Viséan onward, were connected with both the northern (Boreal) and southern (Tethyan) paleogeographical realms. In the late early Carboniferous, the Boreal marine realm had already extended into southern Mongolia (Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991; Afanasjeva, Reference Afanasjeva2016). During the Permian, Mongolian sedimentary sequences were subjected to strong tectonic deformation, and are now preserved only as scattered fragments with complex structural overprints and diverse faunal signatures (Manankov, Reference Manankov2012). Nevertheless, comparative studies of Mongolian basins and faunal provinces in North China, Japan, the South Primorye region (Ussuri Subprovince of the Tethyan Realm), the Kolyma-Omolon superterrane, the Urals, and the Arctic region strongly support the existence of an independent microcontinental unit in southern Mongolia during the late Paleozoic. The continental shelf of this block was characterized by brachiopod faunas with a peculiar admixture of Boreal and Tethyan elements (Manankov et al., Reference Manankov, Shi and Shu-zhong2006; Shi, Reference Shi2006; Manankov, Reference Manankov2008, Reference Manankov2012; Afanasjeva, Reference Afanasjeva2016). This tectonic unit likely functioned as an effective barrier to marine circulation and faunal migration between the northern and southern seaways, resulting in provincialism and distinct compositional differences between the faunal assemblages in different basins along different paleolatitudes during the Kungurian. Northeastern Mongolian basins (e.g., the Khangaï-Khentei geosynclinal zone) contain Kolyma-Omolon-type faunas, whereas those in southern Mongolia (e.g., the Inner Mongolian geosyncline) are dominated by lower-latitude components (Manankov, Reference Manankov and Afanasjeva1995, Reference Manankov and Alekseev2007, Reference Manankov2015). This biogeographic differentiation became even more pronounced during the Guadalupian (middle Permian), when faunal assemblages with strongly mixed biogeographic signals developed in southeastern Mongolia, whereas coeval faunas in central and northern Mongolia lacked any Tethyan warm-water taxa (see Fig. 3; Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991; Manankov, Reference Manankov1998a, Reference Manankovb, Reference Manankov1999, Reference Manankov2012; Manankov et al., Reference Manankov, Shi and Shu-zhong2006; Yin et al., Reference Yin, Zhang and Feng2004; Xiao et al., Reference Xiao, Windley, Liu, Jian, Liu, Yuan and Sun2005; Shi, Reference Shi2006).

However, the composition of the brachiopod fauna in southeastern Mongolia described herein indicates that during the late Cisuralian, the northeastern Tethys was situated in the temperate climatic zone. According to Shi et al. (Reference Shi, Archbold and Zhan1995), the brachiopod assemblage from the Hovsugol area can be broadly grouped into four categories (Fig. 3):

Boreal elements (15 species): These include cold-water species, e.g., Uraloproductus stuckenbergianus (Krotow, Reference Krotow1885); Linoproductus lutkewitschi Stepanov, Reference Stepanov1936; Spitzbergenia ogonerensis (Zavodowsky, Reference Zavodowsky and Markowskii1960); Arctitreta kempei (Andersson in Wiman, Reference Wiman1914); Rhynoleichus delenjaensis; Callaiapsida arctica (Holtedahl, Reference Holtedahl and Holtedahl1924); Tiramnia greenlandica (Dunbar, Reference Dunbar1955); Anidanthus ussuricus (Fredericks, Reference Fredericks1924); Neospirifer koargychanensis Zavodowsky in Zavodowsky and Stepanov, Reference Zavodowsky, Stepanov and Kulikov1971; Spiriferella ovata Lee and Gu, Reference Lee and Gu1976; Spiriferella keilhaviiformis Fredericks, Reference Fredericks1916; Spiriferella keilhavii; Spiriferella praesaranae (Stepanov, Reference Stepanov1948); Alispiriferella lita; and Primorewia reshetnikov;

Endemic species (10 species): These are confined to the Hovsugol area, representing a distinctive regional character of the fauna. Examples include Dyoros (Dyoros) semicircularis, Dyoros (Dyoros) sp. indet., Paramarginifera nativa, Paramarginifera pentagona new species, Linoproductus planiconvexus new species, Heteralosia alexandrae, Camerisma lazarevi, Jilinmartinia hovsugolensis new species, Spiriferella mugunica, and Paeckelmanella latissima;

Antitropical/bipolar taxa: These include species with mid- to high-latitude Permian distributions, previously interpreted by Shi and Grunt (Reference Shi and Grunt2000) as indicative of bipolar faunal distribution patterns. Notable taxa include Magniplicatina undulata Waterhouse, Reference Waterhouse1986a; Magniplicatina transversa Briggs, Reference Briggs1998; Ingelarella atlanicha; Ingelarella plana; Paeckelmanella expansa (Tschernyschew, Reference Tschernyschew1902); Phricodothyris suborbicularis; and Spirelytha fredericksi Archbold and Thomas, Reference Archbold and Thomas1984;

Cosmopolitan species: These are relatively few and include Dyoros (Dyoros) extensiformis; Stenoscisma biplicatum (Stuckenberg, Reference Stuckenberg1898); and Rhynchopora nikitini.

Importantly, no typical Asian Tethyan or Cathaysian taxa have been identified within the Hovsugol brachiopod fauna.

Based on this analysis, the Hovsugol assemblage is dominated by cold-water Boreal elements and locally endemic species (Fig. 3). Although a few antitropical and cosmopolitan taxa are present, the fauna overwhelmingly reflects a high-latitude, cool-water biogeographical character, with a negligible presence of warm-water Tethyan components. This suggests that during the late Cisuralian, the Hovsugol area in southeastern Mongolia was predominantly influenced by cool to temperate climatic conditions probably due to relatively northern position in the Mongolian seaway, which favored the colonization and persistence of high-latitude Boreal faunas.

As discussed earlier, the Permian marine strata of southeastern Mongolia exhibit close sedimentological and paleogeographical affinities with those of adjacent regions, e.g., the Beishan area in northwestern China, the Zhesi and Xiujimqinqi areas of Inner Mongolia, southern Primorye, and parts of Japan (e.g., South Kitakami). These similarities strongly support paleogeographic and paleobiogeographic connectivity among these regions, indicating that the marine basin of southeastern Mongolia is thought to have been part of a broader marine system like the Sino-Mongolian Seaway, or more broadly, the PAO. This seaway encompassed much of northeastern China, the southern part of Primorye in the Russian Far East, and parts of Japan in the east.

Sedimentological and paleontological evidence shows that the Sino-Mongolian seaway persisted through Kungurian and much of the Guadalupian as an extensive epicontinental sea (Manankov et al., Reference Manankov, Shi and Shu-zhong2006; Heumann et al., Reference Heumann, Johnson, Webb, Taylor, Jalbaa and Minjin2012; Eizenhöfer and Zhao, Reference Eizenhöfer and Zhao2018). During this time, the faunal composition remained a Boreal-Tethyan hybrid assemblage (Shen and Shi, Reference Shen and Shi2002, Reference Shen and Shi2009; Shen et al., Reference Shen, Xie, Zhang and Shi2009; Tazawa and Shintani, Reference Tazawa and Shintani2022), a result of the region’s paleogeographical location (25°–35°N), its position along the northeastern margin of Pangea, and its east partly connected with the Panthalassa Ocean. The convergence of warm and cold marine currents facilitated episodic mixing of high-latitude Boreal and paleoequatorial Cathaysian faunas, whereas ongoing tectonic convergence between the Sino-Korean and Bureya-Jiamusi blocks narrowed the seaway during the middle Permian, bringing these previously distinct faunas into geographic proximity (Shi et al., Reference Shi, Shen, Campbell, Raksaskulwong and Weiss2001, Reference Shi, Lee, Kotlyar and Zakharov2022; Shi, Reference Shi2006). Shi et al. (Reference Shi, Lee, Kotlyar and Zakharov2022) compared this Boreal-Tethyan mixing system of the middle Permian to the modern Sea of Japan/East Sea. This semienclosed NE-SW trending basin is influenced by both the warm Tsushima Current (a northeastern branch of the Kuroshio derived from the North Equatorial Current) and the cold Liman Current from the northern Pacific (Minoura et al., Reference Minoura, Akaki, Nemoto, Tsukawaki and Nakamura2012). The benthic invertebrate faunas in the Sea of Japan show dynamic fluctuation and mixing in response to changing oceanographic inputs (Das et al., Reference Das, Singh, Holbourn, Farooq, Vats and Pandey2021). The most striking biotic turnover occurred during an early Pleistocene sea-level highstand, when an influx of warm water through the Tsushima Strait led to extinction of some cold-water specialists and integration of the remaining assemblages (Kitamura et al., Reference Kitamura, Omote and Oda2000). During this event, sea-surface temperatures in the Oki Ridge area rose rapidly from 14°C at 11.6 ka to 19°C at 11.1 ka. This analogy supports the interpretation that the Sino-Mongolian seaway shared similar paleolatitude, oceanic current dynamics, and biotic mixing patterns with the modern Sea of Japan/East Sea, providing a valuable framework for understanding cold-warm faunal convergence in the paleo-oceanographic context of East Asia during the Guadalupian.

Finally, in southeastern Mongolia, Beishan (northwestern China), Zhesi (Inner Mongolia), and southern Primorye (Russian Far East), the hybrid Guadalupian marine fauna, especially brachiopods, was eventually replaced by mixed Angaran-Cathaysian plant assemblages in the late Permian, signaling the regional marine-to-terrestrial transition (Shi and Zhan, Reference Shi and Zhan1996; Deng et al., Reference Deng, Wan and Yang2009). This transformation coincided with the final tectonic assembly of the Sino-Korean, Siberian, and Central Asian blocks (De Jong et al., Reference De Jong, Xiao, Windley and Masago2006; Eizenhöfer and Zhao, Reference Eizenhöfer and Zhao2018; Wu et al., Reference Wu, Shi and Anderson2021). However, radiolarian data from Engeerwusu (Alxa) and floral divergence between the Alxa-North China and Beishan-Sonid regions (Xie et al., Reference Xie, Yin, Zhou and Zhang2014; Bu et al., Reference Bu, He, Zhang, Yu, Wang and Wu2020) indicate that the seaway likely remained open at least into the early Wuchiapingian. This implies diachronous closure of the PAO: the western segment of the PAO likely closed during the early Carboniferous to late Kungurian or Guadalupian; the eastern segment remained open until the Permian-Triassic boundary interval. In particular, oceanic basins in northern Beishan and the southwestern part of the South Tianshan and Japan in the east persisted into the late Permian, with final closure possibly occurring at or even after the end-Permian (Zhang et al., Reference Zhang, Tian, Li, Gong and Xing2013; Bu et al., Reference Bu, He, Zhang, Yu, Wang and Wu2020; Tazawa, Reference Tazawa2024).

Type species

Chonetes consanguineus Girty, Reference Girty1929 (p. 409, figs. 8, 9) from the Delaware Mountain Formation of Wordian age, Texas, USA.

Dyoros ( Dyoros ) semicircularis Afanasjeva, Reference Afanasjeva, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991

Figure 4.1–4.4

Figure 4.

Brachiopods from Hovsugol, southeastern Mongolia. (1–4) Dyoros (Dyoros) semicircularis Afanasjeva, Reference Afanasjeva, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991: ventral view (1) of a ventral valve from bed 5; ventral (2) and posterior (3) views of an internal mold of a ventral valve from bed 5; and dorsal view (4) of a ventral valve from bed 14 (NIGP 208927–208929). (5–7) Dyoros (Dyoros) extensiformis Cooper and Grant, Reference Cooper and Grant1975: ventral views (5, 6) of two ventral valves from bed 7; and dorsal view (7) of a dorsal valve from bed 14 (NIGP 208930–208932). (8, 9) Dyoros (Dyoros) sp. indet.: ventral view (8) of a ventral valve; and internal mold of a ventral valve (9) from bed 14 (NIGP 208933, 208934). (10–17) Probolionia elongata Cooper, Reference Cooper1957: ventral (10), anterior (11), posterior (12), and lateral (13) views of a ventral valve; and ventral (14), anterior (15), posterior (16), and lateral (17) views of an internal mold of a ventral valve, all from bed 5 (NIGP 208935, 208936). (18–25) Uraloproductus stuckenbergianus (Krotow, Reference Krotow1885): ventral (18, 22), anterior (19, 23), posterior (20, 24), and lateral (21, 25) views of two ventral valves from bed 14 (NIGP 208937, 208938). (26–33) Paramarginifera nativa Manankov, Reference Manankov, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991: ventral (26, 30), anterior (27, 31), posterior (28, 32), and lateral (29, 33) views of two ventral valves from bed 5 (NIGP 208939, 208940). c = costellae; ms = median septum.

Reference Afanasjeva, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991 Dyoros (Dyoros) semicircularis Afanasjeva, p. 96, pl. 22, figs. 2–4.

Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Dyoros (Dyoros) semicircularis; Afanasjeva, p. 103, pl. 38, figs. 2–4.

Holotype

An articulated shell from the Hovsogol area, southern Mongolia (Afanasjeva, Reference Afanasjeva, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991, p. 96, pl. 22, fig. 2a, b).

Occurrence

HV-5, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized; semicircular to slightly transversely elliptical in outline, wider than long, widest at hinge (mean shell width/length ratio = 1.477); lateral flanks rounded, anterior margin broadly rounded; anterior commissure faintly to moderately folded toward dorsal valve; ventral valve gently to moderately convex in lateral profile; anterior profile broadly to moderately convex; flanks gently sloping; umbonal region and beak small; sulcus conspicuous and wide, originating from umbo and extending broadly to anterior margin; dorsal valve gently concave in lateral profile, maximum concavity near midvalve or slightly posterior; fold originating on posterior near beak; ventral interior with short median septum anterior to apical area; muscle scars not clear; inner surface finely papillose; dorsal interior with small cardinal process and socket ridges; inner surface strongly papillose; some specimens with weak concentric lines; other features not observed.

Materials

Three ventral valves and four internal molds of ventral valves.

Remarks

The present species is characterized by its semicircular outline, maximum width at hingeline, and a conspicuous, wide sulcus. The specimens described above are from the same horizon of Afanasjeva (Reference Afanasjeva, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991). This species resembles Dyoros (Dyoros) lamellosa Liu and Waterhouse, Reference Liu and Waterhouse1985 (p. 12, pl. 1, figs. 2–6, 9) from the Houtoumiao Formation in Xiujimqinqi, China, in general outline, but the latter has a wider sulcus. The present species is small compared to Dyoros (Dyoros) grandis Afanasjeva, Reference Afanasjeva and Sarycheva1977 (p. 15, pl. 1, figs. 15–18) from the Kungurian lower Starostinskaya Formation of western Spitsbergen. Dyoros (Dyoros) magnus Stehli, Reference Stehli1954 (p. 312, pl. 19, figs. 13–15) from the lower Bone Spring Formation (Kungurian) of Texas is different from the present species by its less convex shells and shallower sulcus. Dyoros (Dyoros) consanguineus Girty, Reference Girty1929 (p. 409, figs. 8, 9) from the Kungurian Bone Spring Formation of West Texas is separated from Dyoros (Dyoros) semicircularis by its longer ears and deeper sulcus. Specimen NIGP 208928 (Fig. 4.2, 4.3) exhibits a slightly different outline and a less anteriorly widening sulcus compared to the other figured specimens. These differences are likely attributable to ontogenetic stage or preservation condition. Because this specimen is an incomplete internal mold with poorly preserved features and comes from the same bed as the other materials, it is regarded as conspecific with Dyoros (Dyoros) semicircularis, and the observed variation is interpreted as falling within the intraspecific range.

Dyoros ( Dyoros ) extensiformis Cooper and Grant, Reference Cooper and Grant1975

Figure 4.5–4.7

Reference Cooper and Grant1975 Dyoros (Dyoros) extensiformis Cooper and Grant, p. 1229, pl. 483, figs. 1–10, pl. 500, figs. 20–32.

Reference Torres-Martínez, Velasco-de-León and Flores-Barragán2024 Dyoros (Dyoros) extensiformis; Torres-Martínez et al., p. 6, fig. 4.1.

Holotype

An articulated shell from Cathedral Mountain Formation, West Texas, USA (Cooper and Grant, Reference Cooper and Grant1975, pl. 500, figs. 20–24).

Occurrence

HV-14; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized; rectangular and transverse in outline, widest at hinge (mean shell width/length ratio = 1.834); ears large and prominent; lateral flanks oblique, anterior margin truncated and emarginate; anterolateral margin a little rounded; anterior commissure broadly folded toward dorsal valve; ventral valve evenly and gently convex; umbonal region weakly swollen; median region moderately swollen; sulcus originating near midvalve, very broad and shallow; lateral slopes to posterolateral margins short and steep, anterior slopes steeper than lateral slopes; dorsal valve moderately deep and concave in median region, concavity extending to umbo and anterolaterally on each side of the broad and low fold; ventral interior finely papillose; dorsal interior unusually marked by regular costellae.

Materials

Three ventral valves and a dorsal valve.

Remarks

The characteristic features of this species are its transverse outline (mean shell width-to-length ratio = 1.834), a broad and low fold, and regular costellae on the inner surface. These Mongolian specimens are almost the same as the material from the Kungurian Cathedral Mountain Formation in West Texas in outline and other described features (Cooper and Grant, Reference Cooper and Grant1975, pl. 483, figs. 1–5). Dyoros (Dyoros) transversus Cooper and Grant, Reference Cooper and Grant1975 (p. 1239, pl. 486, figs. 28–67, pl. 487, figs. 1–17, pl. 501, figs. 1–4) from the Kungurian to Roadian Road Canyon and Cibolo Formations of West Texas resembles the present species in its widely extended hinge and low convexity, but Dyoros (Dyoros) extensiformis is actually not so strongly transverse as Dyoros (Dyoros) transversus (mean shell width-to-length ratio = 2.468) and has more strongly differentiated ears than Dyoros (Dyoros) transversus. Dyoros (Dyoros) extensiformis differs from Dyoros (Dyoros) extensus Cooper and Grant, Reference Cooper and Grant1975 (p. 1230, pl. 483, figs. 11–44) by its lower convexity of the ventral valve and stronger ears.

Dyoros ( Dyoros ) sp. indet.

Figure 4.8, 4.9

Occurrence

HV-14; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized; rectangular and extremely transverse in outline; wider than long; hinge width nearly twice shell length (mean shell width-to-length ratio = 2.303); maximum width at hinge; cardinal extremities subquadrate to acute; anterior commissure straight to weakly folded toward dorsal valve; ventral valve strongly convex laterally and anteriorly, maximum convexity slightly anterior to midvalve; beak small, obtusely pointed; ears prominent, slightly depressed; swollen umbonal region with gentle slopes to ears; sulcus weak, originating slightly posterior to midvalve; dorsal valve deeply concave laterally, maximum concavity near midvalve; umbonal region concave; ears weakly concave, demarcated by oblique ridges; fold low and broadly rounded, originating near midvalve; ventral interior with poorly-preserved short median septum; strong papillose interior; dorsal interior unknown.

Materials

One ventral valve and one internal mold of a ventral valve.

Remarks

This species is extremely transverse, with a weak sulcus that gives it a distinct appearance within the subgenus Dyoros (Dyoros). Dyoros (Dyoros) convexus Cooper and Grant, Reference Cooper and Grant1975 (p. 1227, pl. 482, figs. 6–32, pl. 501, figs. 32–61) from the Wordian Cherry Canyon and Word formations in West Texas, USA closely resembles the present species, but the latter is distinguished by its greater convexity and shallower sulcus in the ventral valve. Considering its transverse outline, this species bears some resemblance to Dyoros (Dyoros) transversus (see Cooper and Grant, Reference Cooper and Grant1975, p. 1239, pl. 486, figs. 28–67, pl. 487, figs. 1–17, pl. 501, figs. 1–4), however the present species is easily recognized by its more rectangular form, its hinge only slightly wider than its midvalve, and a much shallower sulcus. However, due to the scarcity and incompleteness of the available material, especially the lack of articulated shells, it is premature to erect a new species. Thus, these specimens are tentatively referred to as Dyoros (Dyoros) sp. indet.

Suborder Productidina Waagen, Reference Waagen1883 in 1882–1885

Superfamily Productoidea Gray, Reference Gray1840

Family Productellidae Schuchert, Reference Schuchert, Schuchert, LeVene and Pompeckj1929

Subfamily Marginiferinae Stehli, Reference Stehli1954

Genus Probolionia Cooper, Reference Cooper1957

Type species

Probolionia posteroreticulata Cooper, Reference Cooper1957 (p. 27, pl. 7A, figs. 1–23) from the Coyote Butte Formation, Oregon, USA.

Probolionia elongata Cooper, Reference Cooper1957

Figure 4.10–4.17

Reference Cooper1957 Probolionia elongata Cooper, p. 29, pl. 8B, figs. 6–12.

Holotype

A ventral valve from central Oregon, USA (Cooper, Reference Cooper1957, p. 29, pl. 8B, figs. 6–8).

Occurrence

HV-5, 6, 8; Hovsugol, Mongolia; late Cisuralian.

Description

Large; elongate in outline; longer than wide, hinge width approximately half of shell length; body with fine, rounded costellae and concentric undulations cancellated by costellae on visceral disk; trail long, marked by longitudinal costellae; surface covered by fine concentric growth lines; ventral valve with 10 mm long visceral region, geniculating at 90°; geniculated trail nearly twice the length of visceral part, strongly convex laterally; sulcus originating near from beak, extending to front margin, deepest on geniculated portion, shallower anteriorly; broad U-shaped sulcus in section, narrowly rounded trough; beak and umbo elongated, moderately convex; visceral region moderately inflated with steep lateral slopes; visceral region strongly reticulated.

Materials

A total of 14 specimens: six ventral valves, seven internal molds of ventral valves, and an internal mold of an articulated shell.

Remarks

This species is the largest marginiferid found in the Oregon Permian (Cooper, Reference Cooper1957). Besides, it has a strongly convex visceral disk region, a deep sulcus, and strongly rounded flanks. It differs from Probolionia posteroreticulata (see Cooper, Reference Cooper1957, p. 30, pl. 7A, figs. 1–23, text-fig. 2A), by its large size and a shallower, less strongly reticulate visceral disk.

Genus Uraloproductus Ustritskiy, Reference Ustritsky1971

Type species

Productus stuckenbergianus Krotow, Reference Krotow1885 (p. 267, pl. 4, figs. 4–6) from the lower Permian of the Asian Arctic (Russian Federation).

Remarks

The present specimens, with moderately to strongly convex ventral valve, weak to moderate sulcus, and distinct reticulate ornament with concentric rugae, are assigned to Uraloproductus. In outline and sculpture, Uraloproductus resembles Marginifera Waagen, Reference Waagen1884 in 1882–1885 but differs in having a less convex ventral profile and fewer spines. The spines of Marginifera are in prominent rows along the flanks, plus others widely scattered on the venter (Brunton et al., Reference Brunton, Lazarev, Grant, Yu-gan and Kaesler2000, p. 439), whereas the spines of Uraloproductus consist of one pair on the ears, one pair on the posterolateral slopes, and one pair on the trail anteriorly, as well as a few smaller halteroid spines over the umbonal region (Shi and Waterhouse, Reference Shi and Waterhouse1996). Uraloproductus is also very close to Retimarginifera Waterhouse, Reference Waterhouse1970, but it differs by possessing coarser costae, a more transverse outline, and a less concave dorsal valve. Plicatiferina Kalashnikov, Reference Kalashnikov1980 also bears some resemblances to Uraloproductus, but the former has narrow rugae and fine ventral spines. Spyridiophora Cooper and Stehli, Reference Cooper and Stehli1955 can be easily separated with Uraloproductus by its large ears, sessile quadrifid cardinal process, and distinct dorsal adductor platform (spyridium).

Uraloproductus stuckenbergianus (Krotow, Reference Krotow1885)

Figure 4.18–4.25

Reference Krotow1885 Productus stuckenbergianus Krotow, p. 267, pl. 4, figs. 4–6.

Reference Stuckenberg1898 Productus stuckenbergianus; Stuckenberg, p. 262, pl. 4, figs. 47–49.

Reference Tschernyschew1902 Productus stuckenbergi; Tschernyschew, p. 265, pl. 24, fig. 9.

Reference Fredericks1915 Productus stuckenbergianus; Fredericks, p. 48, pl. 3, figs. 12, 13, pl. 4, fig. 7.

Reference Stepanov1934 Productus (Dictyoclostus?) stuckenbergianus; Stepanov, p. 23, pl. 2, figs. 11, 12.

Reference Gerasimov, Devingtal, Zhuravleva, Kaschirzev, Mirskaia, Chudinova and Shestakova1953 Productus stuckenbergi; Gerasimov et al., p. 117, pl. 15, figs. 8, 9.

Reference Mironova1960 Marginifera stuckenbergiana; Mironova, p. 43, pl. 1, figs. 11, 12.

Reference Solomina1960 Marginifera stuckenbergiana; Solomina, p. 63, pl. 12, figs. 2, 3.

Reference Ifanova, Ifanova and Semenova1972 Marginifera (?) stuckenbergiana; Ifanova, p. 117, pl. 6, figs. 10–14.

Reference Solomina and Dubatolov1978 Uraloproductus aff. U. stuckenbergianus; Solomina, p. 111, pl. 9, figs. 17, 18.

Reference Abramov and Grigorjewa1983 Uraloproductus stuckenbergianus; Abramov and Grigorjewa, p. 84, pl. 6, fig. 19.

Reference Kalashnikov, Gorskii and Kalmykova1986 Uraloproductus stuckenbergianus; Kalashnikov, pl. 118, fig. 4.

Holotype

A ventral valve from lower Permian, Asian Arctic (Russia) (Krotow, Reference Krotow1885, p. 267, pl. 4, fig. 4).

Occurrence

HV-5, 11, 12, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Small to medium-sized; subrectangular in outline; concavoconvex without abrupt geniculation; widest at hinge line; anterior commissure moderately folded medially toward dorsal valve; ventral valve moderately to strongly convex, anterior profile weakly convex; visceral disk small; beak incurved, nearly pointed; umbonal region narrow and swollen; trail long and moderately convex; sulcus weak in small specimens to prominent in larger adult specimens, originating 4–6 mm anterior to umbo, broad and shallow; costae weak over umbonal region and ears, distinct on trail, six or seven in 5 mm at midlength, occasionally increasing in number anteriorly by intercalation; rugae strong over the whole valve, crossing costae on anterior part; reticulation distinct; spines few, one large spine base located on the anterior flank with other smaller spine bases observed across the surface of the ventral valve; dorsal fold beginning approximately 5 mm anterior to tip of dorsal umbo, low and broadly extending to anterior margin; ornament similar to ventral valve with more prominent costae over visceral disk; reticulation well developed; some small pits present.

Materials

A total of 24 specimens: 17 ventral valves, five internal molds of ventral valves, an external mold of ventral valve, and an incomplete articulated shell.

Remarks

The subrectangular outline, sculpture, and weak sulcus of these specimens match Uraloproductus stuckenbergianus. Uraloproductus bilobatus (Abramov and Grigorjewa, Reference Abramov and Grigorjewa1988) is close to this species, but differs in its bilobed anterior margin, extensive and somewhat convoluted ears, and large spines on the ears.

Subfamily Productininae Muir-Wood and Cooper, Reference Muir-Wood and Cooper1960

Tribe Paramarginiferini Lazarev, Reference Lazarev, Muravyev and Grigorjewa1986

Genus Paramarginifera Fredericks, Reference Fredericks1916

Type species

Marginifera clarkei Tschernyschew, Reference Tschernyschew1902 (p. 328, 651, pl. 47, figs. 6, 7, pl. 58, figs. 1–3) from the lower Permian (Schwagerina Limestone) of Kasarmensky Kamen on the Sim River, Ural Mountains, Russia.

Paramarginifera nativa Manankov, Reference Manankov, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991

Figure 4.26–4.33

Reference Manankov, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991 Paramarginifera nativa Manankov, p. 104, pl. 25, figs. 7–12.

Reference Manankov, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Paramarginifera nativa; Manankov, p. 118, pl. 43, figs. 11–14.

Holotype

An articulated shell from Hovsogol area, Mongolia (Manankov, Reference Manankov, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991, p. 104, pl. 25, fig. 7a, b).

Occurrence

HV-5, 8, 10, 11, 13, 14, 16; Hovsugol section, Kungurian.

Description

Small to medium-sized; subpentagonal to rounded quadrangular in outline; wider than long, widest at hinge line; anterior commissure slightly folded toward dorsal valve; ventral valve strongly convex; visceral disk broadly large; beak strongly incurved, slightly overhanging hinge line; umbonal region convex with the umbonal angle at 85–90º; strong geniculation beginning at approximately one-third of shell length, trail long and broad; sulcus originating at umbonal region, narrow and shallow; surface with fine costae, prominently bifurcating on trail, ~ 5–7 in 5 mm at midlength; rugae strong and prominent on visceral disk, flanks, and ears; spines few, six large spines nearly symmetrically placed on each side of median sulcus, ear and flank, ~ 2 mm in diameter; other small spines scattered on trail and flanks; dorsal valve moderately concave; fold variably developed on trail, low and indistinct to rather prominent; surface ornament similar to that of ventral valve, but with finer costae and rugae, no spines; interior unknown.

Materials

A total of 45 specimens: mostly ventral valves except for one dorsal shell and three external molds of dorsal valves.

Remarks

The present species closely resembles Paramarginifera auritus Lee and Gu, Reference Lee and Gu1976 (p. 250, pl. 169, figs. 1, 2, 4) from the Guadalupian Zhesi Formation of Inner Mongolia, China in general outline, but differs from the latter because Paramarginifera auritus has larger, pointed ears, and large pustules. Each pustule extends over two or three costae on the ventral geniculation. The present species is less convex and the rugae on the ears are much more prominent when compared with the type species, Paramarginifera clarkei Tschernyschew, Reference Tschernyschew1902 (p. 328, 651, pl. 47, figs. 6, 7, pl. 58, figs. 1–3) from upper Carboniferous to lower Permian of the Urals and Timan. Paramarginifera peregrina Fredericks, Reference Fredericks1924 (p. 24, pl. 1, figs. 7, 8; Fredericks, Reference Fredericks1925, p. 12, pl. 1, figs. 41–44) has stronger rugae over the visceral disk and the ears when compared to Paramarginifera nativa.

Paramarginifera pentagona new species

Figure 5.1–5.14

Figure 5.

Brachiopods from Hovsugol, southeastern Mongolia. (1–14) Paramarginifera pentagona n. sp.: ventral (1, 5), anterior (2, 6), posterior (3, 7), and lateral (4, 8) views of two ventral valves from bed 5; dorsal views (9, 10) of two external molds of two dorsal valves from bed 5 and bed 6; and ventral (11), anterior (12), posterior (13), and lateral (14) views of a ventral valve from bed 8 (NIGP 208941–208945). (15–21) Linoproductus lutkewitschi Stepanov, Reference Stepanov1936: ventral (15, 18), posterior (16, 19), and lateral (17, 20) views of two ventral valves from bed 16; and ventral view (21) of a ventral valve with internal structure from bed 5 (NIGP 208946–208948). (22–26) Linoproductus planiconvexus n. sp.: ventral (22), anterior (23), posterior (24), and lateral (25) views of a ventral valve from bed 7; and ventral view (26) of a ventral valve from bed 8 (NIGP 208949, 208950). (27–35) Anidanthus ussuricus (Fredericks, Reference Fredericks1924): ventral (27), posterior (28), and lateral (29) views of a ventral valve from bed 13; ventral (30), anterior (31), posterior (32), and lateral (33) views of a ventral valve from bed 7; and dorsal views (34, 35) of external molds of two dorsal valves from bed 5 and bed 14 (NIGP 208951–208954). adp = adductor platform; dds = diductor scars.

Holotype

A ventral valve (NIGP 208941) from Bed 5 of the Hovsugol section (Fig. 5.1–5.4).

Diagnosis

Medium-sized to large Paramarginifera with pentagonal to subrectangular outline; ventral valve moderately to extremely convex with shallow sulcus; gradual or abrupt geniculation; small ears with weak to moderate rugae.

Occurrence

HV-5–14, 16; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; wider than long; strongly pentagonal to subpentagonal or subrectangular in outline; hinge line straight, marking the widest part of the shell; anterior commissure rounded or slightly folded dorsally; ventral valve moderately to strongly convex, maximum convexity from anterior third to midvalve; beak strongly incurved; umbonal region convex; geniculation gradual or abrupt; sulcus shallow, originating near umbo, widening anteriorly; ears small, demarcated from visceral disk by steep slopes; rugae weak to moderate, stronger on ears; costae fine, numbering six or seven per 5 mm at midlength; spines few, with six large ones symmetrically arranged on trail, flanks, and ears, with additional small scattered spines; dorsal valve moderately to deeply concave; median fold low, broad; except ventral interior with obscure diductor scars, no other internal structures observed.

Etymology

pentagona, Latin, meaning pentagonal, referring to its pentagonal outline.

Materials

A total of 121 specimens: 91 ventral valves, 25 internal molds of ventral valves, four external molds of dorsal valves, and one internal mold of conjoined shell.

Remarks

This species displays a wide range of convexity and geniculation development, from gradual (as in the holotype) to more abrupt (Fig. 5.11–5.14), the intermediate morphologies indicating continuous intraspecific variation. The new species differs from Paramarginifera clarkei (see Tschernyschew, Reference Tschernyschew1902, p. 328, 651, pl. 47, figs. 6, 7, pl. 58, figs. 1–3; Muir-Wood and Cooper, Reference Muir-Wood and Cooper1960, p. 214, pl. 60, figs. 11–24; Brunton et al., Reference Brunton, Lazarev, Grant, Yu-gan and Kaesler2000, p. 429, fig. 281.1a–d) by having coarser costae and distinct rugae on ears, and from Paramarginifera nativa by its larger size, shallower sulcus, and absence of cincture. Paramarginifera auritus (see Lee and Gu, Reference Lee and Gu1976, p. 250, pl. 169, figs. 1, 2, 4) from Inner Mongolia shares some similarities but differs by having distinctive ventral costae and dorsal pits.

Superfamily Linoproductoidea Stehli, Reference Stehli1954

Family Linoproductoidea Stehli, Reference Stehli1954

Subfamily Linoproductinae Stehli, Reference Stehli1954

Genus Linoproductus Chao, Reference Chao1927

Type species

Productus cora d’Orbigny, Reference d’Orbigny1842 (p. 55, pl. 5, figs. 8, 9) from the upper Carboniferous–lower Permian of Patapatani, an island in Lake Titacaca, and at Yaurichambi, Bolivia.

Linoproductus lutkewitschi Stepanov, Reference Stepanov1936

Figure 5.15–5.21

Reference Stepanov1936 Linoproductus lutkewitschi Stepanov, p. 121, pl. 1, fig. 5.

Reference Lee and Gu1976 Linoproductus lutkewitschi; Lee and Gu, p. 259, pl. 170, fig. 4.

Reference Manankov, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991 Linoproductus lutkewitschi; Manankov, p. 116, pl. 26, figs. 10–13.

Reference Manankov, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Linoproductus lutkewitschi; Manankov, p. 116, pl. 42, figs. 9, 10.

Holotype

A ventral valve from the Productus Limestone in Svalbard Islands, Norway (Stepanov, Reference Stepanov1936, p. 121, pl. 1, fig. 5a–c).

Occurrence

HV-5–8, 16; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; elongate or semicircular in outline; profile evenly convex; widest at hinge line or slightly anterior to it; flanks gently rounded; anterior margin broadly rounded; ventral valve evenly convex; visceral disk inflated; beak small and strongly incurved, slightly overhanging hinge line; umbonal region low and gently swollen; ears in most specimens not well preserved, small and well demarcated, strongly corrugated, undulations extending in concentric bands on lateral slopes but dying out medially; trail long and gently curved from visceral disk without distinct geniculation; median sulcus absent; external surface finely costate, increasing anteriorly by frequent intercalation, separated by interspaces of equal or slightly narrower width; dorsal valve moderately to deeply concave; geniculation not abrupt; trail flatly concave; median fold indistinct or absent; external ornament similar to that of ventral valve but with slightly finer costellae and very weak rugae on visceral disk; no spines observed; ventral interior with slightly raised adductor platform, long and broad, ~ 7 mm wide and 11 mm long, weakly dendritic posteriorly and striated anteriorly, divided by median myophragm; diductor scars flabellate and ridged longitudinally.

Materials

A total of 30 specimens: 23 ventral valves, five internal molds of ventral valves, and two specimens with internal structure of the ventral valves.

Remarks

Our specimens are largely comparable with those described by Manankov (Reference Manankov, Pavlova, Manankov, Morozova, Solovjeva, Suetenko and Bogoslovskaya1991, Reference Manankov, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003) in all observable aspects. Linoproductus superba Reed, Reference Reed1944 (p. 56, pl. 16, figs. 4, 4a) from the top of the middle (or base of the upper) Productus Limestone of the Salt Range, Pakistan differs from Linoproductus lutkewitschi by its larger size and more convex ventral valve. The species Linoproductus philocrinus Stehli, Reference Stehli1954 (p. 319, pl. 21, figs. 6–10) from the lower Bone Spring Formation in the Sierra Diablo Mountains of West Texas, USA resembles the present species in possessing wrinkled ears, but the former can be easily recognized by the absence of body spines and the presence of a strong fold and sulcus.

Linoproductus planiconvexus new species

Figure 5.22–5.26

Holotype

A ventral valve (NIGP 208949) from Bed 7 of the Hovsugol section (Figs. 5.22–5.25).

Diagnosis

Large, oval outline; very low convexity; median sulcus on ventral valve absent; moderately developed rugae on ears.

Occurrence

HV-5, 7, 8, 13, 16; Hovsugol, Mongolia; late Cisuralian.

Description

Large with low convexity; oval in outline; wider than long, maximum width at midvalve or a little posterior to midvalve; ventral beak low, obtusely rounded, scarcely projecting beyond hinge line; umbonal region low, weakly swollen, with short and gently inclined to moderately steep umbonal slopes; ears small, well demarcated by groove, moderately corrugated, undulations extending in concentric bands on posterolateral slopes, dying out quickly toward anterolateral slopes; median sulcus absent; external surface covered entirely by rather fine costae, radial costellae rounded, increasing from beak to anterior margin by intercalation, numbering approximately nine in 5 mm at 10 mm from umbo, seven in 5 mm at midlength, the interspaces of these costellae slightly wider than costae; double row of large, suberect spines along hinge margin, very few spines observed on rest of valve; ventral interior with large diductor scars, longitudinally striate; adductor scars a little more posteriorly placed, long and dendritic; dorsal interior unknown.

Etymology

plani, Latin, meaning flat; convexus, Latin, meaning convex, well rounded; altogether referring to its low convexity.

Materials

A total of 10 specimens: eight ventral valves and two internal molds of ventral valves.

Remarks

The characteristic features of the new species mainly include a very low convexity of the ventral valve, moderately rugose ears, and the absence of a median sulcus. Linoproductus meniscus Dunbar and Condra, Reference Dunbar and Condra1932 (p. 255, pl. 30, figs. 4, 5) from the Home Creek Limestone of the Canyon Group is said to have low convexity and very few spines, but it is still more convex than Linoproductus planiconvexus n. sp. in lateral profile and has more prominent spine bases on the ventral valve. Although the surface costae of Linoproductus latiplanus Ivanov, Reference Ivanov1935 (p. 44, pl. 6, fig. 7) are very similar to those of the present species, the lateral view of Linoproductus latiplanus (see Ivanov, Reference Ivanov1935, fig. 7b) obviously indicates its very strong convexity. Linoproductus antiqua Stepanov, Reference Stepanov1948 (p. 21, pl. 4, figs. 5, 6) from the lower Permian of Zilime, Russia has a similar outline and external ornamentation to Linoproductus planiconvexus n. sp., but the former seems to be larger, reaching 80 mm in width and 70 mm in length, with less rugose ears. Further comparisons between the two species are hindered because Stepanov (Reference Stepanov1948) did not show a lateral view of Linoproductus antiqua. Linoproductus planiventralis Hoare, Reference Hoare1960 (p. 228, pl. 32, figs. 1–3) from the upper Carboniferous of southwestern Missouri, USA closely resembles the present species in having pronounced mesial flattening and very few spines on the ventral valve, but in comparison, has large ears with strong wrinkles and strong lengthwise convexity of the ventral valve.

Subfamily Anidanthinae Waterhouse, Reference Waterhouse1968b

Genus Anidanthus Hill, Reference Hill1950

Type species

Linoproductus springsurensis Booker, Reference Booker1932 (p. 67, pl. 3, figs. 1–6) from the Artinskian in Springsure Dome, Nebo District, Mountain Britton and Yatton Goldfield, Queensland, Australia.

Remarks

The specimens exhibit key features shared by Anidanthus and Megousia Muir-Wood and Cooper, Reference Muir-Wood and Cooper1960, e.g., a transversely expanded outline, bifurcate or intercalated costellae, overlapped lamellae, and similar dorsal interior structures. However, the absence of large crescentic ears with radial ornamentation—typical of Megousia—supports their cautious assignment to Anidanthus.

Anidanthus ussuricus (Fredericks, Reference Fredericks1924)

Figure 5.27–5.35

Reference Fredericks1924 Productus ussuricus Fredericks, p. 8, pl. 1, figs. 1–5.

Reference Nakamura1972 Anidanthus ussuricus; Nakamura, p. 434, pl. 1, fig. 1a–c.

Reference Lee and Gu1976 Anidanthus ussuricus; Lee and Gu, p. 260, pl. 163, figs. 4–6.

Reference Licharew, Kotlyar and Popeko1978 Anidanthus ussuricus; Licharew and Kotlyar, pl. 13, fig. 5.

Reference Lee, Gu and Su1980 Anidanthus ussuricus; Lee et al., p. 379, pl. 170, figs. 5, 9.

Reference Lee, Gu and Li1984 Anidanthus ussuricus; Lee et al., pl. 2, figs. 8, 16.

Reference Duan and Li1985 Anidanthus ussuricus; Duan and Li, p. 113, pl. 38, figs. 6–9.

Reference Tazawa and Hasegawa2007 Anidanthus ussuricus; Tazawa and Hasegawa, p. 6, fig. 4.1–4.7.

Holotype

A complete shell from Ussuri, South Primorye, Russia (Fredericks, Reference Fredericks1924, p. 8, pl. 1, figs. 1–5).

Occurrence

HV-5–9, 13–16; Hovsugol, Mongolia; late Cisuralian.

Description

Small to medium-sized; transversely subrectangular to broadly triangular in outline; moderately to strongly concavoconvex, much wider than long; ventral valve moderately to strongly convex; visceral disk regularly convex, with a gradual geniculation from the anterior margin of visceral disk; hinge line straight, marking greatest shell width; umbo relatively narrow, strongly inflated, slightly to moderately incurved beyond hinge line; ventral beak sharply pointed, strongly incurved, extending beyond hinge line slightly; ears narrow, flattened, well demarcated from visceral disk; ventral sulcus absent or very weak; surface finely costellate, costae low and rounded, 10–13 in 5 mm on the midvalve, increasing in number by intercalation on trail toward anterior margin; weak rugae on ears and flanks; body spines scattered in small numbers on anterior slope; dorsal valve moderately concave; visceral disk moderately large, deeply concave; trail relatively short; dorsal fold absent or too weak to be perceptible; dorsal surface costae similar to that of the ventral valve, but with concentric lamellae developed; ventral interior with anteriorly placed adductor scars and diductor scars; dorsal interior with obscure cardinal process and brachial ridges.

Materials

A total of 180 specimens: 118 ventral valves, 28 molds of ventral valves, two dorsal valves, 28 external molds of dorsal valves, three articulated shells, and an external mold of an articulated shell.

Remarks

The material includes a medium-sized shell with coarse radial costae and lacks both a median sulcus on the ventral valve and a fold on the dorsal valve, which suggests assignment to Anidanthus ussuricus (Fredericks, Reference Fredericks1924, p. 8, pl. 1, figs. 1–5). Anidanthus megensis Solomina, Reference Solomina1981 (p. 68, pl. 6, figs. 4, 5), from the upper Sakmarian Megen Suite of the Verkhoyansk Mountains, is considerably larger, with more developed ears and a less convex ventral valve, although it shares a similar costal density. Anidanthus cessnockensis Briggs, Reference Briggs1998 (p. 201, fig. 96A–I), from the Artinskian Tiverton Formation of the northern Bowen Basin, Queensland, Australia, differs in its markedly more transverse outline and larger shell size. Anidanthus victori Abramov and Grigorjewa, Reference Abramov and Grigorjewa1988 (p. 133, pl. 9, figs. 12–15), from the lower Permian of the Verkhoyansk Mountains, Russia, displays a similar outline to Anidanthus ussuricus but is smaller and bears numerous finer spines on the ventral valve. Anidanthus parvimucronata He and Shen, Reference He, Shen, He, Shi, Zhang, Yang, Shen and Zhang2019 (nomen novum, for Anidanthus mucronata He and Shen in He et al., Reference He, Shen, Feng and Gu2005, p. 929, fig. 3.1–3.15), from the latest Changhsingian of Guangxi, South China, closely resembles Anidanthus ussuricus in general appearance, but differs in its significantly smaller size and distinctly mucronate cardinal extremities.

Family Monticuliferidae Muir-Wood and Cooper, Reference Muir-Wood and Cooper1960

Subfamily Auriculispininae Waterhouse, Reference Waterhouse1986a

Genus Magniplicatina Waterhouse, Reference Waterhouse1983a

Type species

Cancrinella magniplica Campbell, Reference Campbell1953 (p. 7, pl. 1, figs. 1–8) from the Ingelara and Barfield formations of the Bowen Basin, Queensland, eastern Australia.

Remarks

The genus Magniplicatina was established for species resembling Cancrinella Fredericks, Reference Fredericks1928 in their swollen ventral valves, but distinguished by strong ventral rugae and spines restricted to the ventral valve. Helenaeproductus Lazarev, Reference Lazarev1991 with Helenaeproductus khubsugulensis (Lazarev, Reference Lazarev1991) from southeastern Mongolia as its type, was later synonymized with Magniplicatina by Brunton et al. (Reference Brunton, Lazarev, Grant, Yu-gan and Kaesler2000). As noted by Briggs (Reference Briggs1998), fine, closely spaced rugae are common in Linoproductidae, but only species with coarse, prominent rugae belong in Magniplicatina. The genus differs from Cancrinella in lacking dorsal spines, having stronger ventral rugae and more widely spaced ventral spines, and generally larger shells. Compared to Costatumulus Waterhouse, Reference Waterhouse1983b, which also lacks dorsal spines, Magniplicatina is distinguished by its coarser rugae and larger ventral spine bases.

Magniplicatina undulata Waterhouse, Reference Waterhouse1986a

Figure 6.1–6.10

Figure 6.

Brachiopods from Hovsugol, southeastern Mongolia. (1–10) Magniplicatina undulata Waterhouse, Reference Waterhouse1986a: ventral (1, 5), anterior (2, 6), posterior (3, 7), and lateral (4, 8) views of two ventral valves from bed 5; and dorsal view (9, 10) of external molds of two dorsal valves from bed 5 and bed 14 (NIGP 208955–208958). (11–14) Magniplicatina transversa Briggs, Reference Briggs1998: ventral (11), posterior (12), and lateral (13) views of a ventral valve; and dorsal view (14) of an external mold of a dorsal valve, all from bed 5 (NIGP 208959, 208960). (15–17) Magniplicatina sp. indet.: ventral (15), posterior (16), and lateral (17) views of a ventral valve from bed 5 (NIGP 208961). (18–26) Spitzbergenia ogonerensis (Zavodowsky, Reference Zavodowsky and Markowskii1960): ventral (18), anterior (19), posterior (20), and lateral (21) views of a ventral valve; ventral (22), anterior (23), posterior (24), and lateral (25) views of an internal mold of a ventral valve; and dorsal view (26) of an external mold of a dorsal valve; all from bed 14 (NIGP 208962–208964). (27–32) Heteralosia alexandrae Pavlova in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991: ventral (27, 29) and dorsal (28, 30) views of internal molds of two articulated shells from bed 5; dorsal view (31) of a dorsal valve from bed 5; and dorsal view (32) of an external mold of a dorsal valve from bed 7 (NIGP 208965–208968). ads = adductor scars; cp = cardinal process; isr = inner socket ridges; mr = median ridge; ms = median septum; s = spines; soc = sockets.

Reference Waterhouse1986a Magniplicatina undulata Waterhouse, p. 45, pl. 9, figs. 17–20.

Reference Briggs1998 Magniplicatina undulata; Briggs, p. 188, fig. 92A–I.

Holotype

Mold of specimen with conjoined shells from the Elvinia Formation, Bowen Basin, southeastern Queensland, Australia (Waterhouse, Reference Waterhouse1986a, p. 45, pl. 9, fig. 19).

Occurrence

HV-5, 7, 8, 14–16; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; subquadrate to subrectangular or longitudinally elongate; moderately to strongly concavoconvex; generally wider than long; ventral valve moderately to strongly convex, with greatest convexity at anterior visceral disk; hinge line straight, equal to or slightly shorter than shell width; umbo small, strongly incurved, beak extending beyond hinge line; ears small, flat, sharply or moderately demarcated from visceral disk; surface with fine, regularly spaced costae, crossed by distinct concentric rugae; rugae strength varying from moderate to strong, often more prominent on ears and lateral slopes; radial costae increasing via intercalation; spines moderately abundant, developed over whole valve; dorsal fold; dorsal valve moderately concave; costae and rugae similar to those of ventral valve but usually lower; dorsal spines absent; interior with weakly preserved adductor and diductor scars; cardinal process bilobed; median septum low, elongate; spine bases and internal ridges occasionally preserved.

Materials

A total of 194 specimens: 73 ventral valves, 85 internal molds of ventral valves, 10 external molds of ventral valves, two dorsal valves, five internal molds of dorsal valve, 15 external molds of dorsal valves, and four articulated shells.

Remarks

This species can be readily distinguished from Magniplicatina magniplica (Campbell, Reference Campbell1953) (p. 7, pl. 1, figs. 1–8) from the Ingelara and Barfield formations of Bowen Basin, Queensland, eastern Australia, by its lower and more closely spaced rugae and coarser costae over the surface. A ventral valve illustrated by Liu and Waterhouse (Reference Liu and Waterhouse1985, p. 17, pl. 1, fig. 11) from the Houtoumiao Formation (possibly of Artinskian age) of Inner Mongolia was referred to as Magniplicatina sp. indet. Despite its relatively smaller size, the similar overall appearance still places it within Magniplicatina. Magniplicatina gigantea Shen, Shi, and Archbold, Reference Shen, Shi and Archbold2003 (p. 78, pl. 9, figs. 7–16) from the Qubuerga Formation (Lopingian) in the Mt. Qomolangma region, southern Tibet, China, differs from Magniplicatina undulata by its much coarser costae (approximately five or six in 5 mm on the trail) and its coarser spines.

Magniplicatina transversa Briggs, Reference Briggs1998

Figure 6.11–6.14

Reference Briggs1998 Magniplicatina transversa Briggs, p. 187, pl. 91, figs. A–J.

Holotype

An articulated shell from Colarine Mudstone, southern New England Orogen (Briggs, Reference Briggs1998, p. 187, pl. 91, figs. D–F).

Occurrence

HV-5, 7, 8, 13, 14, 16; Hovsugol, Mongolia; late Cisuralian.

Description

Small to medium-sized; transversely oval to semielliptical in outline; wider than long; maximum width at midvalve or slightly anterior; ventral valve flatly or weakly convex; hinge line straight; umbonal region small, somewhat strongly incurved, slightly beyond hinge line; beak strongly incurved; ventral ears small, flat, triangular, demarcated from visceral disk by groove; no sulcus on ventral valve; surface finely costate with strong rugae; costellae crossed by strong concentric rugae, 13 or 14 in 5 mm at midvalve; rugae prominent over venter, stronger on flanks and ears, weaker over disk; spines along hinge and ears slightly coarser than body spines; dorsal valve weakly concave; visceral disk large, broad, flatly concave; no dorsal fold developed; ears triangular and flat, well demarcated from the visceral disk; surface costellae are finer and rugae slightly less elevated than those of ventral valve; ventral interior with weakly and smoothly impressed scars.

Materials

A total of 100 specimens: 30 ventral valves, 34 internal molds of ventral valves, four external molds of ventral valves, three dorsal valves, four internal molds of dorsal valves, 24 external molds of dorsal valves, and one incomplete articulated shell.

Remarks

Magniplicatina transversa differs from Magniplicatina undulata by its smaller size (mean shell length = 21.81 mm, mean shell width = 28.97 mm in Magniplicatina transversa vs. mean length = 25.93 mm, mean width = 32.19 mm in Magniplicatina undulata), weaker ventral convexity, and exceptionally low and densely spaced rugae. Magniplicatina perflecta Waterhouse, Reference Waterhouse1986a (p. 47, pl. 10, figs. 6–11) from the Oxtrack Formation (Kungurian) of Bowen Basin, eastern Australia, differs from the present species by its large size, equidimensional shape, and relatively strongly inflated ventral valve.

Magniplicatina sp. indet.

Figure 6.15–6.17

Occurrence

HV-5; Hovsugol section, Kungurian.

Description

Medium-sized; elongate oval outline; strongly concavoconvex; ventral valve strongly convex; visceral disk large, strongly convex, with gradual geniculation toward anterior margin; hinge line not well preserved; umbonal region strongly incurved; ventral ears small, well demarcated from visceral disk; no ventral sulcus; surface finely costate, costellae crossed by strong, concentric rugae; rugae stronger on flanks and ears, weaker over disk; spines few on ventral valve; no dorsal fold developed; surface costella and rugae similar to those on ventral valve.

Materials

One ventral valve and one external mold of dorsal valve.

Remarks

The lateral view of the ventral specimen examined during this study looks very like one of the figures of Magniplicatina magniplica shown by Campbell (Reference Campbell1953, p. 7, pl. 1, fig. 8), but it differs in having a much longer shell and less elevated rugae. These two incomplete specimens can hardly be placed in Magniplicatina khubsugulensis Lazarev, Reference Lazarev1991, Magniplicatina undulata, or Magniplicatina transversa as described above.

Genus Spitzbergenia Kotlyar in Grigorjewa, Ganelin, and Kotlyar, Reference Grigorjewa, Ganelin, Kotlyar and Sarytcheva1977

Type species

Productus loveni Wiman, Reference Wiman1914 (p. 72, pl. 17, figs. 12–18) from the Selander Formation (Permian), Spitsbergen.

Spitzbergenia ogonerensis (Zavodowsky, Reference Zavodowsky and Markowskii1960)

Figure 6.18–6.26

Reference Zavodowsky and Markowskii1960 Cancrinella ogonerensis Zavodowsky, p. 65, pl. 1, figs. 13, 14, 16.

Reference Zavodowsky, Stepanov and Kulikov1971 Cancrinella ogonerensis; Zavodowsky and Stepanov, p. 106, pl. 64, figs. 4–6.

Reference Grigorjewa, Ganelin, Kotlyar and Sarytcheva1977 Cancrinelloides ogonerensis; Grigorjewa et al., p. 151, pl. 24, figs. 4–8.

Reference Abramov and Grigorjewa1988 Cancrinelloides? ogonerensis; Abramov and Grigorjewa, p. 128, pl. 11, figs. 15, 16, pl. 12, figs. 1, 2.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Spitzbergenia ogonerensis; Pavlova et al., p. 114, pl. 26, fig. 7.

Holotype

A ventral valve from Ogoner Creek, Omolon River, Russia (Zavodowsky, Reference Zavodowsky and Markowskii1960, p. 65, pl. 1, fig. 13).

Occurrence

HV-5, 7, 14, 15; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; quadrangular to transversely oval in outline; wider than long; ventral valve moderately to strongly convex; ears small, flat; ventral visceral disk moderately large, roundly triangular; hinge line straight, less than greatest shell width; umbonal region generally small, strongly incurved, with relatively short, steep umbonal slopes; ventral beak strongly incurved, slightly extending beyond hinge line; surface with fine costae and moderately developed rugae; costae 12–14 in 5 mm around midlength, increasing in number by intercalation; rugae also on ears and lateral slopes; spines numerous, recumbent, thin, erect on ears and flanks; dorsal valve moderately concave with gently concave visceral disk; gradual geniculation toward anterior margin; no dorsal fold developed; dorsal surface ornamentation similar to that of ventral valve but without spines; ventral interior with elongate, branching adductors, diductor scars enclosing adductor scars anteriorly.

Materials

A total of 51 specimens: 31 ventral valves, 12 internal molds of ventral valves, one specimen with internal structure of a ventral, one dorsal valve, four external molds of dorsal valves, and two incomplete articulated shells.

Remarks

Spitzbergenia ogonerensis is close to Spitzbergenia gracilis Kotlyar in Grigorjewa, Ganelin, and Kotlyar, Reference Grigorjewa, Ganelin, Kotlyar and Sarytcheva1977 (p. 157, pl. 25, fig. 10, pl. 26, figs. 1–5) in general features, but differs in having a more convex ventral valve, stronger rugae on its ears, and slightly fewer ventral spines. Spitzbergenia ogonerensis differs from Spitzbergenia loveni from the Selander Formation (Permian), Spitsbergen in its smaller shell size, gentle geniculation, and much less steep flanks.

Suborder Strophalosiidina Schuchert, Reference Schuchert, von Zittel and Eastman1913

Superfamily Strophalosioidea Schuchert, Reference Schuchert, von Zittel and Eastman1913

Family Strophalosiidae Schuchert, Reference Schuchert, von Zittel and Eastman1913

Subfamily Strophalosiinae Schuchert, Reference Schuchert, von Zittel and Eastman1913

Genus Heteralosia King, Reference King1938

Type species

Heteralosia slocomi King, Reference King1938 (p. 278, pl. 39, figs. 15–18) from the Graham Formation (Pennsylvanian), Texas of USA.

Heteralosia alexandrae Pavlova in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991

Figure 6.27–6.32

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Heteralosia alexandrae Pavlova in Pavlova et al., p. 100, pl. 22, figs. 12–15.

Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Heteralosia alexandrae; Afanasjeva et al., p. 111, pl. 41, figs. 4–6.

Holotype

An articulated shell from the Hovsugol area, southern Mongolia (Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991, p. 100, pl. 22, fig. 13).

Occurrence

HV-5–8, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; transversely semicircular to oval in outline; wider than long; ventral valve moderately to strongly convex, maximum convexity around visceral disk; hinge line nearly straight, less than greatest shell width; ventral interarea distinct, flat or slightly concave; delthyrium narrow, triangular, with weakly convex pseudodeltidium; umbonal region small with distinct cicatrix of attachment; ventral beak region small, not well preserved in most specimens; ears generally small, flat; no ventral sulcus; surface with spines and concentric lamellae; spines distributed as row along hinge, body spines spaced at intervals of 1.5 mm at midlength and anterior margin, mostly lying at low angle to surface or recumbent on surface; dorsal valve moderately concave; dorsal visceral disk gently concave; umbonal region slightly swollen and convex; no dorsal fold; spines absent on dorsal valve, but with some weak concentric lamellae or fine growth markings; ventral interior with divergent teeth; muscle area bisected by low median ridge; adductor scars large, forming on small raised platform; diductor scars fairly large, weakly striate; weak marginal ridge present posteriorly, flattening and becoming indistinct anteriorly; anterior of ventral interior nearly smooth; dorsal interior with bilobed cardinal process supported by strong median septum; sockets small but deep, surrounded by inner socket ridges; median septum slightly more than half of valve length; dorsal adductor scars smooth, distinct, slightly raised, somewhat pear-shaped.

Materials

A total of 113 specimens: one incomplete ventral valve, 8 internal molds of ventral valves, one external mold of ventral valve, one specimen with internal structure of a ventral, one incomplete dorsal valve, nine internal molds of dorsal valves, 90 external molds of dorsal valves, and two internal molds of articulated shells.

Remarks

This species was established by Pavlova (in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991) from the Hovsugol area of southeastern Mongolia, roughly the same area from which the present specimens were collected. The majority of our specimens show a high degree of similarity to those described by Pavlova, with some being morphologically indistinguishable from the original material. Heteralosia alexandrae is close to Heteralosia mexicana Cooper, Reference Cooper1953 (p. 28, pl. 7A, figs. 1–3) in outline, but the latter differs in being smaller with more spines on the ventral valve, with ~ 15 spines observed within a 5 × 5 mm area near the central anterior region, compared to ~ 10 in Heteralosia alexandrae. Heteralosia etheridgei (Prendergast, Reference Prendergast1943) (Archbold, Reference Archbold1986, p. 105, fig. 3A–Z, AA, BB) from the Permian of Western Australia differs from the present species by its much smaller shell size and stronger ventral convexity. The specimens described as Heteralosia haerens Grant, Reference Grant1976 (p. 83, pl. 18, figs. 1–28) from the upper part of lower Permian of Thailand are distinguished by their tiny shell size, few spines, and no real median septum.

Order Orthotetida Waagen, Reference Waagen1884 in 1882–1885

Suborder Orthotetidina Waagen, Reference Waagen1884 in 1882–1885

Superfamily Orthotetoidea Waagen, Reference Waagen1884 in 1882–1885

Family Schuchertellidae Williams, Reference Williams1953

Subfamily Streptorhynchinae Stehli, Reference Stehli1954

Genus Streptorhynchus King, Reference King1850

Type species

Terebratulites pelargonatus von Schlotheim, Reference von Schlotheim1816 (p. 28, pl. 8, figs. 21–24) from the Lopingian (upper Permian) of Zechstein, Germany.

Streptorhynchus sp. indet.

Figure 7.1–7.6

Figure 7.

Brachiopods from Hovsugol, southeastern Mongolia. (1–6) Streptorhynchus sp. indet.: ventral (1) and lateral (2) views of an articulated shell from bed 5; ventral (3), dorsal (4), and lateral (5) views of an articulated shell from bed 5; and dorsal view (6) of a dorsal valve from bed 14 (NIGP 208969–208971). (7–9) Arctitreta kempei (Andersson in Wiman, Reference Wiman1914): ventral (7), dorsal (8), and lateral (9) views of an articulated shell from bed 5 (NIGP 208972). (10–19) Rhynoleichus delenjaensis Abramov and Grigorjewa, Reference Abramov and Grigorjewa1983: ventral (10, 15), dorsal (11, 16), anterior (12, 17), posterior (13, 18), and lateral (14, 19) views of two articulated shells from bed 14 and bed 15 (NIGP 208973, 208974). (20–25) Stenoscisma biplicatum (Stuckenberg, Reference Stuckenberg1898): ventral (20), dorsal (21), anterior (22), posterior (23), and lateral (24) views of an articulated shell from bed 13; and dorsal view (25) of a dorsal valve from bed 14 (NIGP 208975, 208976). (26–30) Camerisma lazarevi Pavlova in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991: ventral (26), dorsal (27), anterior (28), posterior (29), and lateral (30) views of an incomplete articulated shell from bed 5 (NIGP 208977). ms = median septum; spd = spondylium.

Occurrence

HV-5, 8, 14, 16; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; slightly semicircular to subconical in outline; moderately biconvex or somewhat convex-planar; wider than long; ventral umbo small, moderately swollen; ventral interarea apsacline; hinge line nearly straight, approximately equal to greatest shell width; cardinal extremities subangular to bluntly rounded; ventral median fold very low, mostly weak or indistinct among specimens collected; surface ornamentation of fine costae, growth increments, and concentric rugae; costae narrow, sharply elevated with broader interspaces, increasing by frequent intercalation, eight or nine in 5 mm over midlength of both valves; crests of costae narrowly rounded; growth increments fine over entire shell; concentric rugae low, six or seven on ventral valve; dorsal valve somewhat more inflated than ventral valve; umbonal region small, weakly swollen; ornament on dorsal valve similar to that of ventral valve, but rugae slightly lower or indistinct; dorsal interior with low, broad cardinalia; cardinal process small and obscure.

Materials

A total of 22 specimens: three ventral valves, five dorsal valves, nine internal molds of dorsal valves, one internal mold of dorsal valve, one external mold of dorsal valve, and three articulated shells.

Remarks

Our specimens can be assigned to the genus Streptorhynchus based on their subconical outline, apsacline ventral interarea, and relatively robust costae; the nomenclature is left open.

Family Schuchertellidae Williams, Reference Williams1953

Subfamily Streptorhynchinae Stehli, Reference Stehli1954

Genus Arctitreta Whitfield, Reference Whitfield1908

Type species

Arctitreta pearyi Whitfield, Reference Whitfield1908 (p. 57, pl. 2, figs. 1–4) from the Kungurian beds of Cape Sheridan, Ellesmere Island, Canadian Arctic Archipelago.

Arctitreta kempei (Andersson in Wiman, Reference Wiman1914)

Figure 7.7–7.9

Reference Wiman1914 Streptorhynchus kempei Andersson in Wiman, p. 58, pl. 10, figs. 22–27, pl. 11, figs. 1–10, pl. 12, figs. 1–8, pl. 13, figs. 11–13.

Reference Frebold1931 Streptorhynchus kempei; Frebold, p. 19, 29, 41, pl. 6, figs. 1–3.

Reference Stepanov1937a Streptorhynchus kempei; Stepanov, p. 109, pl. 1, figs. 2, 6.

Reference Dunbar1955 Streptorhynchus kempei; Dunbar, p. 63, pl. 1, figs. 1–13, pl. 32, figs. 9, 10.

Reference Harker and Thorsteinsson1960 Streptorhynchus kempei; Harker and Thorsteinsson, p. 50, pl. 15, figs. 1–6.

Reference Brabb and Grant1971 Arctitreta cf. A. kempei; Brabb and Grant, p. 14, pl. 2, figs. 21, 22, 25.

Reference Stehli and Grant1971 Arctitreta kempei; Stehli and Grant, p. 510, pl. 61, figs. 9–26.

Reference Manankov1979 Arctitreta kempei; Manankov, p. 76, pl. 6, figs. 1–4.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Arctitreta kempei; Pavlova et al., p. 94, pl. 22, figs. 10, 11.

Reference Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Arctitreta kempei; Afanasjeva et al., p. 97, pl. 36, figs. 5, 6.

Type specimens

Holotype not designated; all specimens illustrated by Andersson (in Wiman, Reference Wiman1914, p. 58, pl. 10, figs. 22–27, pl. 11, figs. 1–10, pl. 12, figs. 1–8, pl. 13, figs. 11–13) from Flowers Valley, Uppsala, Sweden constitute the syntypic series.

Occurrence

HV-5, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Small to medium-sized; elongate to triangular in outline; moderately biconvex; maximum width at anterior one-third of shell length; cardinal extremities subrounded; ventral valve weakly to moderately convex; umbonal region gently convex, anterior moderately convex or gradually increasing in convexity; umbo prominent, suberect, slightly distorted; interarea moderately high and triangular; delthyrium narrow, covered by a distinctly convex pseudodeltidium; no ventral median sulcus; surface with fine radial costellae and weak concentric rugae; costae narrowly rounded with slightly wider interspaces, increasing in number by intercalation, numbering nine or ten in 5 mm over midlength of both valves; concentric rugae very weak, three or four on ventral valve; dorsal valve slightly more convex than opposite valve; dorsal interarea low and nearly linear; dorsal valve with weaker or lower rugae compared to the ventral valve; internal structures not well preserved, only muscle field impressed on internal molds.

Materials

A total of 11 specimens: five ventral valves, three dorsal valves, and three incomplete articulated shells.

Remarks

The present species differs from Arctitreta peelensis Shi and Waterhouse, Reference Shi and Waterhouse1996 (p. 46, pl. 1, figs. 15, 19–24) from the upper Jungle Creek Formation (lower Permian) of the northern Yukon Territory, Canada by its less elongate outline, larger muscle field, and finer costellae. Arctitreta kempei differs from the type species Arctitreta pearyi (see Whitfield, Reference Whitfield1908, p. 57, pl. 2, figs. 1–4) from the Kungurian beds of Cape Sheridan, Ellesmere Island, Canadian Arctic Archipelago in being much smaller and having finer costellae. Arctitreta bapensis Waterhouse and Rao, Reference Waterhouse and Rao1989 (p. 26, fig. 3.1–3.4) from the Asselian Bap Formation of Peninsula India is similar to the present species in size and overall shape but is distinguished by its finer costellae on the dorsal valve (12–24 in 5 mm near midlength), and broader umbonal region. Arctitreta percostata Waterhouse, Reference Waterhouse1982 (p. 341, pl. 1, figs. 1–7) from the pebbly mudstones of southern Thailand in the Phuket Group of Asselian (possibly lower Sakmarian) differs from Arctitreta kempei in having stronger rugae and a weak sulcus on both ventral and dorsal valves.

Order Rhynchonellida Kuhn, Reference Kuhn1949

Superfamily Pugnaoidea Rzhonsnitskaia, Reference Rzhonsnitskaia and Guzman1956

Family Pugnacidae Rzhonsnitskaia, Reference Rzhonsnitskaia and Guzman1956

Genus Rhynoleichus Abramov and Grigorjewa, Reference Abramov and Grigorjewa1983

Type species

Rhynoleichus delenjaensis Abramov and Grigorjewa, Reference Abramov and Grigorjewa1983 (p. 96, pl. 11, figs. 8, 9) from the upper Carboniferous of the west Verkhoyansk Region, Russia.

Rhynoleichus delenjaensis Abramov and Grigorjewa, Reference Abramov and Grigorjewa1983

Figure 7.10–7.19

Reference Abramov and Grigorjewa1983 Rhynoleichus delenjaensis Abramov and Grigorjewa, p. 96, pl. 11, figs. 8, 9, text-fig. 23.

Reference Abramov and Grigorjewa1988 Rhynoleichus delenjaensis; Abramov and Grigorjewa, p. 141, pl. 15, figs. 8–14, 18, 20, text-figs. 45, 46.

Holotype

An articulated, three-dimensionally preserved shell from Verchoyan Mountains, eastern Siberia, Russia, within the Sakha Republic (Yakutia) (Abramov and Grigorjewa, Reference Abramov and Grigorjewa1983, p. 96, pl. 11, fig. 8a, b).

Occurrence

HV-5, 7, 14, 15; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; strongly and unequally biconvex; wider than long, with greatest width at approximately two-thirds length of shell from beak; anterior commissure strongly folded dorsally; ventral valve gently convex, relatively stronger convexity over umbonal region, anteriorly flat to slightly concave; umbo small, low, slightly extended with small circular foramen; umbonal slopes very short and steep; sulcus beginning from midlength, quickly widening and deepening toward the anterior margin, delimited by high, steep sides, broadly U-shaped in section, occupying half to two-thirds of shell width at front; anterior tongue pronounced, short, deeply indenting dorsal valve; surface smooth, but sulcus carrying four or five slightly high, broad costae, arising simultaneously with sulcus with sharp crest and low, well-rounded interspaces; concentric lines weak; dorsal valve strongly convex (much more convex than ventral valve); dorsal fold broad, high, with four or five high, sharp-crested costae, separated by deep, angular interspaces; concentric growth lines weak; ventral interior with short, thick dental plates; dorsal interior with moderately long median septum.

Materials

Ten specimens: two ventral valves, one internal mold of ventral valve, one internal mold of dorsal valve, and six articulated shells.

Remarks

Rhynoleichus dsilensis Pavlova in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 (p. 123, pl. 29, fig. 1) from the upper Permian of southern Mongolia differs from Rhynoleichus delenjaensis by its larger size, less sharp costae, and more rounded sides. As pointed out by Shi and Waterhouse (Reference Shi and Waterhouse1996), Rhynoleichus dorsoconvexa (Shi and Waterhouse, Reference Shi and Waterhouse1996, p. 108, pl. 20, figs. 1–13) from the Permian of northern Yukon Territory, Canada approaches the present species in many aspects, however, the Yukon species only has two costae over the sulcus and fold, and the shell is larger (mean length = 25.23 mm, width = 32.17 mm) than our Mongolian specimens (mean length = 17.88 mm, width = 22.73 mm).

Superfamily Stenoscismatoidea Oehlert, Reference Oehlert and Fischer1887

Family Stenoscismatidae Oehlert, Reference Oehlert and Fischer1887

Subfamily Stenoscismatinae Oehlert, Reference Oehlert and Fischer1887

Genus Stenoscisma Conrad, Reference Conrad1839

Type species

Terebratula schlottheimii von Buch, Reference von Buch1834 (p. 59, pl. 2, fig. 32a–c) from the middle Zechstein (upper Permian), Germany.

Stenoscisma biplicatum (Stuckenberg, Reference Stuckenberg1898)

Figure 7.20–7.25

Reference Stuckenberg1898 Camarophoria biplicata Stuckenberg, p. 230, pl. 3, fig. 18.

Reference Tschernyschew1902 Camarophoria biplicata; Tschernyschew, p. 83, pl. 50, figs. 8–10.

Reference Licharew and Einor1939 Camarophoria biplicata; Licharew and Einor, p. 71, pl. 14, fig. 6.

Reference Kulikov1974 Stenoscisma biplicata; Kulikov, p. 94, pl. 5, fig. 3.

Reference Liao1979 Stenoscisma biplicata; Liao, pl. 3, figs. 11, 12.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Stenoscisma biplicatum; Pavlova et al., p. 120, pl. 28, figs. 7, 8.

Reference Fan and He1999 Stenoscisma biplicata; Fan and He, p. 129, pl. 23, figs. 6, 7.

Reference Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Stenoscisma biplicatum; Afanasjeva et al., p. 72, pl. 17, fig. 7.

Holotype

An articulated, three-dimensionally preserved shell from Suksunsky Log, western Ural, Russia (Stuckenberg, Reference Stuckenberg1898, p. 230, pl. 3, fig. 18).

Occurrence

HV-5, 7, 8, 13–15; Hovsugol, Mongolia; late Cisuralian.

Description

Small; broadly subtriangular to triangular in outline; wider than long, with greatest width at two-thirds of length of shell from beak; cardinal extremities rounded; anterior commissure moderately to strongly folded toward dorsal valve; ventral valve gently convex; umbo small, strongly incurved, with umbonal angle ~ 90°; beak strongly incurved, partly to completely covering top of dorsal valve; sulcus beginning slightly anterior to midvalve, broad, shallow, deeping gradually toward anterior margin, extending into truncated tongue; surface with simple costae, relatively fine and low, becoming coarser anteriorly; costae rounded, 2–4 on sulcus but typically only two large, conspicuous costae; concentric lines weak; dorsal valve moderately convex, anterior profile broadly domed, with strongest convexity around midvalve; dorsal fold broad, moderately high, originating slightly posterior to midvalve; anterior margin of fold strongly deflected dorsally; surface with 2–4 costae developed, two conspicuous or stronger costae on fold; ventral interior with strong V-shaped spondylium formed by two conjunct dental plates; median septum moderately high.

Materials

A total of 18 specimens: six ventral valves, one internal mold of ventral valve, four dorsal valves, an internal mold of a dorsal valve, and six articulated shells.

Remarks

Stenoscisma biplicatum is characterized by its small size, broadly subtriangular to triangular outline, biconvex shell, two large, conspicuous costae, and strong V-shaped spondylium inside the ventral valve. It most closely resembles Stenoscisma quasimutabilis Waterhouse, Reference Waterhouse1981 (p. 91, pl. 19, figs. 3–17, pl. 20, figs. 1–6) from the Ko Yao Noi Formation of Artinskian in southern Thailand, with its triangular shell and broad sulcus, but differs in its smaller size, and by having fewer costae on the sulcus and fold, fewer and weaker costae over the flanks, and a dorsal valve that is more convex than the ventral valve. Stenoscisma multicosta Stehli, Reference Stehli1954 (p. 339, pl. 25, figs. 7–9) from the Kungurian Bone Spring Formation in West Texas, USA differs from present species by its large shell, and abundant and relatively fine costation.

Genus Camerisma Grant, Reference Grant1965

Type species

Camerisma prava Grant, Reference Grant1965 (p. 66, pl. 8, fig. 1a, b) from the upper Mississippian limestone, Craig Quadrangle, southeastern Alaska, USA.

Camerisma lazarevi Pavlova in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991

Figure 7.26–7.30

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Camerisma lazarevi Pavlova in Pavlova et al., p. 122, pl. 28, figs. 3–5.

Reference Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Camerisma lazarevi; Afanasjeva et al., p. 72, pl. 17, figs. 8, 9.

Holotype

An articulated shell from Hovsugol area, Mongolia (Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991, p. 122, pl. 28, fig. 3a–c).

Occurrence

HV-5, 8, 9; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; elongated subtriangular to angular in outline; longer than wide; greatest width close to anterior margin; anterior commissure moderately to strongly uniplicate; ventral valve somewhat elongate, moderately convex, greatest convexity around posterior part of valve; umbo small, strongly incurved with short, steep, slightly concave umbonal slopes; beak short, thick, recurved against dorsal umbo; sulcus originating slightly posterior to midlength, broad, shallow; surface smooth, with fine concentric growth lines; dorsal valve strongly convex, anterior profile strongly convex along crest of dorsal fold; dorsal beak strongly incurved into ventral umbo; dorsal fold originating not far from umbo, broad, low, gradually widening and heightening anteriorly with rounded crest; some specimens with weak, wide, moderately high fold; surface with concentric growth lines and growth laminae similar to those of ventral valve; ventral interior with dental plates forming spondylium elevated on median septum; dorsal interior with camarophorium.

Materials

A total of 15 specimens: nine ventral valves and six articulated shells.

Remarks

Basically, the specimens of Camerisma lazarevi described here are identical with those described by Pavlova (in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991) in all observed features. Camerisma rhomboidea Liu and Waterhouse, Reference Liu and Waterhouse1985 (p. 26, pl. 5, figs. 23, 24, pl. 6, figs. 1–4) from the middle Permian of Inner Mongolia, differs from the present species by its rhomboidal outline, deep sulcus, and the costae on the ventral sulcus and dorsal fold. Camerisma rasililaterensis Solomina, Reference Solomina and Dubatolov1978 (p. 113, pl. 9, figs. 25–28; see also Abramov and Grigorjewa, Reference Abramov and Grigorjewa1983, p. 103, pl. 15, figs. 1–6) from the mid-Carboniferous Syorgan Suite of Verchoyan, Siberia, is closely related to Camerisma lazarevi, but differs in having a transverse shell and fine costae on the ventral sulcus. Compared to Camerisma lazarevi, Camerisma judomaensis Abramov, Reference Abramov1974 (p. 83, pl. 2, figs. 1, 2) has a weaker ventral sulcus and stronger concentric growth lines or concentric growth laminae.

Family Psilocamaridae Grant, Reference Grant1965

Subfamily Cyrolexinae Carlson and Grant, Reference Carlson, Grant and Kaesler2002

Genus Callaiapsida Grant, Reference Grant1971

Type species

Camerisma (Callaiapsida) kekuensis Grant, Reference Grant1971 (p. 330, pl. 3, figs. 11–17, 22) from the Halleck Formation, Kuiu Island and Keku Islets, Alaska, USA.

Callaiapsida arctica (Holtedahl, Reference Holtedahl and Holtedahl1924)

Figure 8.1–8.10

Figure 8.

Brachiopods from Hovsugol, southeastern Mongolia. (1–10) Callaiapsida arctica (Holtedahl, Reference Holtedahl and Holtedahl1924): ventral (1, 6), dorsal (2, 7), anterior (3, 8), posterior (4, 9), and lateral (5, 10) views of two articulated shells from bed 5 (NIGP 208978, 208979). (11–14) Rhynchopora nikitini Tschernyschew, Reference Tschernyschew1885: ventral view (11) of a ventral valve from bed 15; dorsal views (12, 13) of two dorsal valves from bed 14; and ventral view (14) of an external mold of a ventral valve from bed 14 (NIGP 208980–208983). (15–20) Cleiothyridina bajkurica (Tschernjak, Reference Tschernjak, Ustritsky and Tschernjak1963): ventral (15), dorsal (16), anterior (17), posterior (18), and lateral (19) views of an articulated shell from bed 5; and dorsal view (20) of an internal mold of a dorsal valve from bed 14 (NIGP 208984, 208985). (21–30) Jilinmartinia hovsugolensis n. sp.: ventral (21, 26), dorsal (22, 27), anterior (23, 28), posterior (24, 29), and lateral (25, 30) views of two articulated shells from bed 7 and bed 14 (NIGP 208986, 208987). (31–35) Tiramnia greenlandica (Dunbar, Reference Dunbar1955): ventral (31), dorsal (32), anterior (33), posterior (34), and lateral (35) views of an articulated shell from bed 14 (NIGP 208988). mf = muscle field; mr = median ridge.

Reference Holtedahl1911 Camarophoria pentameroides Holtedahl, p. 19, pl. 2, figs. 5, 6.

Reference Holtedahl and Holtedahl1924 Camarophoria sella var. arctica Holtedahl, p. 34, pl. 21, figs. 1, 2.

Reference Licharew and Einor1939 Camarophoria sella var. arctica; Licharew and Einor, p. 69, 208, pl. 14, fig. 5a, b.

Reference Gobbett1963 Laevicamera cf. L. arctica; Gobbett, p. 128, pl. 16, figs. 13–16.

Reference Ustritsky, Ustritsky, Chunfa, Qinglin, Jingzhi and Yunjie1963a Laevicamera pentameroides; Ustritsky, p. 100, pl. 27, fig. 14, pl. 28, fig. 1.

Reference Grant1971 Camerisma (Callaiapsida) arctica; Grant, p. 327, pl. 3, figs. 1–10, 18–21.

Holotype

An articulated shell from Ural, Russia (Holtedahl, Reference Holtedahl and Holtedahl1924, p. 19, pl. 21, figs. 1, 2).

Occurrence

HV-5, 7, 8, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Large; outline rhomboid to wedge-like; moderately to strongly biconvex in lateral profile, dorsal valve more convex than ventral valve; wider than long; greatest width anterior to midlength; anterior commissure strongly uniplicate with high fold on dorsal valve and deep sulcus on ventral valve, producing effect of slightly narrow gothic arch from anterior view with crest normally deflected slightly left or right; surface ornament weak, mostly with light to moderate concentric growth lines; ventral anterior tongue long, deeply V-shaped; surface with concentric growth lines regularly distributed; ventral interior thickened at posterior; spondylium relatively large, wide, long, posteriorly inserting into shell wall, anteriorly isolated from posterior wall and supported by median septum; dorsal interior less thickened; cardinal process large; camarophorium buried by umbonal thickening, extending forward, supported by high and massive median septal duplex.

Materials

A total of 63 specimens: 26 ventral valves, four internal molds of ventral valves, one external mold of ventral valve, 29 articulated shells, and three incomplete internal molds of articulated shells.

Remarks

As discussed by Grant (Reference Grant1971, p. 328), Callaiapsida arctica is characterized by its large size, wide and rhomboid outline, sharp and high fold, deep and V-shaped ventral sulcus, and moderately convex ventral valve. One of the closest species to Callaiapsida arctica is Callaiapsida kekuensis from the Halleck Formation of the Kuiu Island and Keku Islets, southeastern Alaska, USA, of probable Artinskian age. However, according to Grant (Reference Grant1971), Callaiapsida kekuensis has on average a larger shell, the sharp fold is farther forward, and its sulcus and fold project forward rather than wrapping around the anterior to become perpendicular to the commissure as in Callaiapsida arctica. Callaiapsida alcaldei Martínez-Chacón, Reference Martínez-Chacón1977 (p. 211, pl. 29, figs. 1–7, text-fig. 3) and Callaiapsida paucicostata Martínez-Chacón, Reference Martínez-Chacón1977 (p. 214, pl. 29, figs. 8–12, text-figs. 4, 5) from Valdeteja and San Emiliano formations of Bashkirian age, Oviedo and Leon, Spain are close to the present species in general outline and gothic arch anterior view, but they are distinguished by their smaller size and less well developed peripheral grooves.

Superfamily Rhynchoporoidea Muir-Wood, Reference Muir-Wood1955

Family Rhynchoporidae Muir-Wood, Reference Muir-Wood1955

Subfamily Rhynchoporinae Muir-Wood, Reference Muir-Wood1955

Genus Rhynchopora King, Reference King1865

Type species

Terebratula geinitziana de Verneuil, Reference de Verneuil, Murchison, Verneuil and Keyserling1845 (p. 83, pl. 10, fig. 5a, b) from the lower Kazanian of North Dvina River Basin, Shidrovo, northern European Russia.

Rhynchopora nikitini Tschernyschew, Reference Tschernyschew1885

Figure 8.11–8.14

Reference Tschernyschew1885 Rhynchopora nikitini Tschernyschew, p. 295, pl. 18, figs. 34–36.

Reference Tschernyschew1889 Rhynchopora nikitini; Tschernyschew, p. 275, pl. 6, fig. 20a–c.

Reference Nikitin1890 Rhynchopora nikitini; Nikitin, p. 70, pl. 3, fig. 14a, b.

Reference Netschajew1894 Rhynchopora nikitini; Netschajew, p. 178, pl. 5, fig. 14a, b.

Reference Stuckenberg1898 Rhynchopora nikitini; Stuckenberg, p. 228, pl. 3, figs. 11, 12.

Reference Tschernyschew1902 Rhynchopora nikitini; Tschernyschew, p. 73.

Reference Kozlowski1914 Rhynchopora nikitini; Kozlowski, p. 84, pl. 9, figs. 67–70.

Reference Stepanov1937b Rhynchopora nikitini; Stepanov, p. 59, pl. 7, figs. 6–11, pl. 12, figs. 1, 2.

Reference Sarytcheva and Sokolskaja1952 Rhynchopora nikitini; Sarytcheva and Sokolskaja, p. 238, pl. 68, fig. 410.

Reference Gobbett1963 Rhynchopora nikitini; Gobbett, p. 129, pl. 16, figs. 18–21.

Reference Mironova1967 Rhynchopora nikitini; Mironova, p. 41.

Reference Abramov1970 Rhynchopora nikitini; Abramov, p. 133, pl. 17, figs. 7–10.

Reference Kulikov1974 Rhynchopora nikitini; Kulikov, p. 95, pl. 5, fig. 8a–e.

Reference Nikolskaya1979 Rhynchopora nikitini; Nikolskaya, p. 46, pl. 2, figs. 2–4.

Reference Zhang, Zhang, Zhang and Wang1983 Rhynchopora nikitini; Zhang et al., p. 330, pl. 135, fig. 2a–e, pl. 136, fig. 4a–e.

Type specimens

Holotype not designated; all specimens illustrated by Tschernyschew (Reference Tschernyschew1885, p. 295, pl. 18, figs. 34–36) from the Russian Platform, Russia constitute the syntypic series.

Occurrence

HV-5, 9, 13–15; Hovsugol, Mongolia; late Cisuralian.

Description

Small to medium-sized; transversely subpentagonal to pentagonal in outline; wider than long, greatest width around midlength; moderately and unequally biconvex with flattened or weakly convex ventral valve and much more inflated dorsal valve in lateral view; anterior commissure moderately to strongly uniplicate with relatively high fold on dorsal valve and moderately deep sulcus on ventral valve; surface costae prominent, originating from beak, posteriorly fine, low, rounded, becoming higher and wider anteriorly still with rounded crests; generally six costae over sulcus and five or six on each flank, separated by very narrow and angular interspaces; very fine, weak concentric growth lines; ventral interior with indistinct dental plates; dorsal interior with long median septum that extends to midlength.

Materials

A total of 44 specimens: 15 ventral valves, one external mold of ventral valve, 27 dorsal valves, and one external mold of dorsal valve.

Remarks

The Mongolian material appears to be identical to Rhynchopora nikitini from the Sakmarian fauna of the Russian Platform and the Urals that was revised by Nikolskaya (Reference Nikolskaya1979, p. 46, pl. 2, figs. 2–4). The Mongolian specimens studied herein are similar to the specimens described as Rhynchopora nikitini in the above synonymy list. Rhynchopora magna Cooper, Reference Cooper1957 (p. 55, pl. 9B, figs. 11–14, pl. 10D, figs. 18–31), from the Coyote Butte Formation of central Oregon is very similar in overall appearance to the present species, but it is distinguished by its larger size, deeper sulcus, and higher fold. Rhynchopora culta Waterhouse, Reference Waterhouse1982 (p. 345, pl. 2, figs. 6–11) from the early Permian fauna of the pebbly mudstone in southern Thailand is also close to the present species in having a shallow sulcus and low fold, but it differs in having a larger size, subtriangular shape, and one or two fewer pairs of costae. Rhynchopora tchernyshae (see Koczyrkevicz, Reference Koczyrkevicz and Gramm1979, p. 47, pl. 11, figs. 1–4) from the lower Barabash Formation in the Barabash section of South Primorye is close to Rhynchopora nikitini in having a small size and pentagonal outline, but the former differs from the latter by its deeper sulcus and higher fold. Rhynchopora variabilis (see Stuckenberg, Reference Stuckenberg1898, p. 228, pl. 3, figs. 13, 14; Tschernyschew, Reference Tschernyschew1902, p. 488, pl. 21, figs. 16, 17; Biernat and Birkenmajer, Reference Biernat and Birkenmajer1981, pl. 7, figs. 1–11, pl. 8, figs. 1–7) is distinguished by its subelliptical shell with stronger and fewer costae on both dorsal and ventral valves.

Order Athyridida Boucot, Johnson, and Staton, Reference Boucot, Johnson and Staton1964

Suborder Athyrididina Boucot, Johnson, and Staton, Reference Boucot, Johnson and Staton1964

Superfamily Athyridoidea Davidson, Reference Davidson1881

Family Athyrididae Davidson, Reference Davidson1881

Subfamily Cleiothyridininae Alvarez, Rong, and Boucot, Reference Alvarez, Jiayu and Boucot1998

Genus Cleiothyridina Buckman, Reference Buckman1906

Type species

Atrypa pectinifera Sowerby, Reference Sowerby1840 (p. 14, pl. 616) from the Magnesian Limestone (upper Permian), England.

Cleiothyridina bajkurica (Tschernjak, Reference Tschernjak, Ustritsky and Tschernjak1963)

Figure 8.15–8.20

Reference Tschernjak, Ustritsky and Tschernjak1963 Composita bajkurica Tschernjak, p. 121, pl. 46, figs. 1, 2.

Reference Grunt and Sarycheva1977 Cleiothyridina bajkurica; Grunt, p. 79, pl. 13, figs. 1–6, text-figs. 24–28.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Cleiothyridina bajkurica; Pavlova et al., p. 139, pl. 32, figs. 7, 8.

Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Cleiothyridina bajkurica; Afanasjeva, p. 170.

Holotype

An articulated shell from the Baykur Formation in eastern Taimyr, Russia (Tschernjak, Reference Tschernjak, Ustritsky and Tschernjak1963, p. 121, pl. 46, fig. 1a–c).

Occurrence

HV-4, 5, 7–9, 13, 14, 16; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized; transversely subcircular to slightly oval in outline; wider than long, greatest width near midlength or slightly posterior to midlength; weakly to moderately biconvex; anterior commissure rectimarginate; umbo relatively small, with short, blunt beak; ventral median sulcus rather shallow to absent; concentric growth lamellae pronounced on surface, seven in 5 mm at 6 mm from ventral umbo, and eight or more in 5 mm near anterior margin; small radial spines developed along each lamella; dorsal fold weak to absent; surface with concentric growth lamellae and small spines similar to those of ventral valve; ventral interior with well-defined dental plates; teeth small; muscle field relatively large; dorsal interior with prominent median ridge.

Materials

A total of 113 specimens: 38 ventral valves, 19 internal molds of ventral valves, 10 external molds of ventral valves, 17 dorsal valves, 12 internal molds of dorsal valves, one external mold of dorsal valve, 11 articulated shells, and five internal molds of articulated shells.

Remarks

The current species was first named by Tschernjak in 1963 from the upper Paleozoic of Taimir. Tschernjak proposed this species under the genus Composita Brown, Reference Brown1849, however, Grunt (Reference Grunt and Sarycheva1977, p. 79) revised it to the genus Cleiothyridina based on complete specimens with well-preserved spines and dorsal interiors (Grunt, Reference Grunt and Sarycheva1977, p. 81). Later, Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991) described the species Cleiothyridina bajkurica from the Hovsugol area of southeastern Mongolia. Our specimens are identical to or closely comparable with those described by Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991) but are smaller than the specimens described by Tschernjak (Reference Tschernjak, Ustritsky and Tschernjak1963). Cleiothyridina ovalis Shi in Archbold and Shi, Reference Archbold and Shi1993 (p. 193, fig. 4A–P) from the Jimba Calcarenite of the Wooramel Group (lower Artinskian, Cisuralian) in the Carnarvon Basin, Western Australia is similar in general appearance to Cleiothyridina bajkurica but is distinguished by its larger shell on average, prominent ventral sulcus and dorsal fold, and its distinct uniplicate anterior commissure. Cleiothyridina semiconcava Waagen, Reference Waagen1884 in 1882–1885 (p. 481, pl. 41, figs. 4–6) from the upper Kungurian to lower Guadalupian Amb Formation of the Salt Range, Pakistan is close to the present species in having a transversely subcircular outline, but it differs in having a much more convex dorsal valve and more strongly folded anterior commissure. Cleiothyridina pseudobajkurica Abramov and Grigorjewa, Reference Abramov and Grigorjewa1983 (p. 116, pl. 17, figs. 5–9, text-fig. 40) from the Carboniferous of the southern Verkhoyansk region is close to Cleiothyridina bajkurica in appearance, but it differs in having a variable shell shape and distinct ventral sulcus.

Order Spiriferida Waagen, Reference Waagen1883 in 1882–1885

Suborder Spiriferidina Waagen, Reference Waagen1883 in 1882–1885

Superfamily Martiniioidea Waagen, Reference Waagen1883 in 1882–1885

Family Martiniidae Waagen, Reference Waagen1883 in 1882–1885

Subfamily Martiniinae Waagen, Reference Waagen1883 in 1882–1885

Genus Jilinmartinia Lee and Gu in Lee, Gu, and Su, Reference Lee, Gu and Su1980

Type species

Brachythyris shansiensis Chao, Reference Chao1929 (p. 55, pl. 9, figs. 1–3) from the Miaokou Limestone of the Taiyuan Formation (Asselian) in the Yuehmenkou section, western of Taiyuan City, Shanxi, northern China.

Remarks

The specimens described here are assigned to the genus Jilinmartinia based on their subcircular outline, biconvex shell with a more convex ventral valve, pointed and overhanging beak, broad vertically striated ventral interarea, and the presence of distinct delthyrial ridges and concentric growth lines. These characters conform well to the diagnosis of Jilinmartinia as revised by Lee and Gu in Lee, Gu, and Su (Reference Lee, Gu and Su1980). Although the genus Martinia M’Coy, Reference M’Coy1844 is morphologically similar in general outline, Jilinmartinia differs from it in having prominent delthyrial ridges and more pronounced concentric growth lines. Following Carter and Gourvennec (Reference Carter, Gourvennec and Selden2006), Kalitvella Lazarev and Poletaev, Reference Lazarev, Poletaev, Ramsbottom, Saunders and Owens1982 is regarded as a junior synonym of Jilinmartinia, further supporting our generic assignment.

Jilinmartinia hovsugolensis new species

Figure 8.21–8.30

Holotype

An articulated shell (NIGP 208986) from Bed 7 of the Hovsugol section (Fig. 8.21–8.25).

Diagnosis

Large for genus, elongately subcircular outline, moderately biconvex in lateral profile; sulcus weakly developed, mostly recognizable close to anterior margin, dorsal fold weakly to moderately developed; surface with conspicuous concentric growth lines.

Occurrence

HV-5, 7, 14–16; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; length 24–49 mm, width 30–46 mm, elongately subcircular to broadly triangular in outline; slightly longer than wide, greatest width close to midlength or slightly posterior to midlength; moderately to strongly biconvex shell with ventral valve more convex than dorsal valve in lateral view; sides and anterior margin rounded; anterior commissure weakly uniplicate; ventral umbo small, strongly inflated, with strongly incurved beak slightly overhanging hingeline; interarea moderately high; median sulcus rather weak, broad and shallow; external surface mostly smooth except for closely distributed concentric growth lines; dorsal beak short and pointed; dorsal fold weak to moderately developed, generally forming low fold medially; surface with concentric growth lines similar to those of ventral valve; ventral interior without dental plates; ventral muscle scars and vascular impressions partly observed.

Etymology

Hovsugol, the name of a small town in southeastern Mongolia, -ensis, Latin, means geographical location; altogether refers to the species collected from the Hovsugol Section in southeastern Mongolia.

Materials

A total of 14 specimens: three ventral valves, two internal molds of ventral valves, and nine articulated shells.

Remarks

Specimens of this species show variation in shell width and thickness, reflecting differences in overall globosity. To evaluate this, we measured shell length, width, and thickness in 10 well-preserved specimens and performed bivariate correlation analyses (see Fig. 9). Shell length shows moderate to strong positive correlations with both width (Fig. 9.1, R² = 0.7678) and thickness (Fig. 9.2, R² = 0.5273), suggesting that globosity increases with size. The specimen NIGP 208987 (Fig. 8.26–8.30), marked in orange in Figure 9, is more globose but still within the species’ variation range, likely reflecting intraspecific variability rather than taxonomic difference. Jilinmartinia yanjiensis Lee and Gu in Lee, Gu, and Su, Reference Lee, Gu and Su1980 (p. 488, pl. 1, fig. 17) from the lower Permian in Jilin in northeastern China is close to the new species in shell size, outline, and surface ornamentation, but Lee and Gu’s species differs from the specimens here described by its higher interarea and more prominent anterior tongue. The new species is differentiated from the type species Jilinmartinia shansiensis (see Chao, Reference Chao1929, p. 55, pl. 9, figs. 1–3) by its more circular outline, shorter hingeline, and less distinct median sulcus. Jilinmartinia tianshanensis Chen, Reference Chen2004 (p. 43, pl. 8, figs. 1–6, 9, 10) from the lower Permian of the Tarim Basin, northwestern China differs from the current new species by its more developed ventral sulcus and stronger uniplicate anterior commissure.

Figure 9.

Scatter plots showing the relationships among shell dimensions of Jilinmartinia hovsugolensis n. sp. from the Hovsugol section, southeastern Mongolia: (1) correlation between shell length (L) and width (W); (2) correlation between shell length (L) and thickness (T). Regression equations and coefficients of determination (R²) are shown for each plot. The specimen NIGP 208987 (Fig. 8.26–8.30), marked here in orange, is more globose but still within the species’ variation range.

Genus Tiramnia Grunt, Reference Grunt and Sarycheva1977

Type species

Martinia uralica Tschernyschew, Reference Tschernyschew1902 (p. 183, 566, pl. 18, figs. 1–4) from the Asselian of Urals in Russia.

Tiramnia greenlandica (Dunbar, Reference Dunbar1955)

Figures 8.31–8.35, 10.1–10.5

Figure 10.

Brachiopods from Hovsugol, southeastern Mongolia. (1–5) Tiramnia greenlandica (Dunbar, Reference Dunbar1955): ventral (1), dorsal (2), anterior (3), posterior (4), and lateral (5) views of an articulated shell from bed 16 (NIGP 208989). (6–15) Ingelarella atlanicha (Kotlyar, Reference Kotlyar and Popeko1978): ventral (6, 11), dorsal (7, 12), anterior (8, 13), posterior (9, 14), and lateral (10, 15) views of two incomplete articulated shells from bed 15 (NIGP 208990, 208991). (16–23) Ingelarella plana Campbell, Reference Campbell1960: ventral (16) and posterior (17) views of a ventral valve from bed 9; ventral (18), posterior (19), and lateral (20) views of a ventral valve from bed 5; and ventral (21), anterior (22), and posterior (23) views of a ventral valve with internal structure from bed 4 (NIGP 208992–208994). ads = adductor scars; dds = diductor scars; dp = dental plates; mg = median groove; ms = median septum.

Reference Dunbar1955 Martinia greenlandica Dunbar, p. 152, pl. 30, figs. 1–8.

Reference Grunt and Sarycheva1977 Tiramnia greenlandica; Grunt, p. 64, pl. 11, figs. 4–6, text-fig. 12.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Tiramnia greenlandica; Pavlova et al., p. 136, pl. 30, figs. 13, 14, 16.

Reference Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Tiramnia greenlandica; Afanasjeva et al., p. 160, pl. 62, figs. 5–7.

Holotype

A three-dimensional body fossil from central East Greenland (Dunbar, Reference Dunbar1955, p. 152, pl. 30, figs. 1–4).

Occurrence

HV-5, 14, 15; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; subcircular or subrounded in outline with the widest part at midlength; sides and anterior margin rounded; moderately to strongly biconvex shell with ventral valve more convex than dorsal valve in lateral view; cardinal extremities broadly rounded; anterior commissure uniplicate; ventral umbo prominent with beak strongly incurved over apex of ventral delthyrium; median sulcus absent in posterior shell and obscurely placed close to anterior margin, extending toward anterior commissure as a linguliform extension; surface mostly smooth, only fine concentric growth lines observed on posterolateral slopes of shell surface; dorsal beak short and obtusely pointed; umbo small, umbonal region moderately high; dorsal fold weak; surface smooth, fine concentric growth lines similar to those of ventral valve internally; ventral median groove bisecting muscle field; a few lateral pallial markings weakly distributed.

Materials

A total of 28 specimens: two ventral valves, one internal mold of dorsal valve, and 25 articulated shells.

Remarks

Tiramnia uralica (Tschernyschew, Reference Tschernyschew1902) (p. 183, 566, pl. 18, figs. 1–4) from the Asselian to Sakmarian Stage of the Urals in Russia resembles the current species in general appearance, but it differs in its much larger shell size, more elongate outline, and finer external concentric growth lines. Tiramnia tschaikensis Grunt, Reference Grunt and Sarycheva1977 (p. 67, pl. 11, fig. 7) from the upper Carboniferous of Siberia and the Arctic differs from Tiramnia greenlandica by its very elongate shell outline and prominent ventral sulcus. Tiramnia semiglobosa (Tschernyschew, Reference Tschernyschew1902) (p. 564, pl. 17, figs. 6–10, 12, 13) from the Cisuralian of the Urals and Timan is also similar to Tiramnia greenlandica in its size and general outline, but the former is recognized by its slightly more convex dorsal valve and higher umbo. Tiramnia yakutica Solomina, Reference Solomina and Dubatolov1978 (p. 121, pl. 11, figs. 12–15) from the upper Carboniferous of the north Verkhoyan region is close to the present species in its weak to indistinct ventral sulcus, but it differs in having a more triangular outline and lower convexity of the ventral valve.

Family Ingelarellidae Campbell, Reference Campbell1959

Subfamily Ingelarellinae Campbell, Reference Campbell1959

Genus Ingelarella Campbell, Reference Campbell1959

Type species

Ingelarella angulata Campbell, Reference Campbell1959 (p. 345, pl. 56, fig. 4a–c, pl. 57, figs. 1–5) from the lower to middle Permian of the Ingelara Shale, Queensland, Australia.

Diagnosis

Medium-sized to very large; biconvex, typically transverse with maximum width at or anterior to hinge line; fold and sulcus generally present but variably developed; sulcus can bear median groove and occasionally pair of weak plicae; lateral slopes smooth or with several broad, low plicae; anterior commissure usually uniplicate, often modified by lateral plicae; ventral umbo typically high; surface microornament consists of elongate grooves arranged in subquincuncial pattern, internally, both valves possess well-developed adminicula; dorsal median septum absent; weak myophragm commonly present; spires directed posterolaterally.

Ingelarella atlanicha (Kotlyar, Reference Kotlyar and Popeko1978)

Figure 10.6–10.15

Reference Kotlyar and Popeko1978 Tomiopsis atlanichus Kotlyar, p. 74, pl. 11, figs. 7–9.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Ingelarella atlanicha; Pavlova et al., p. 137, pl. 30, figs. 11, 12.

Reference Shi, Lee, Kotlyar and Zakharov2022 Ingelarella atlanicha; Shi et al., p. 11, fig. 5L, M.

Holotype

A ventral valve from southern Primorye, Russian Far East (Kotlyar, Reference Kotlyar and Popeko1978, p. 74, pl. 11, figs. 7–9).

Occurrence

HV-14, 15; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; wider than long (mean length = 27.66 mm, width = 33.96 mm); transversely semicircular to subcircular in outline, widest part anterior to hinge line; biconvex shell with ventral valve more convex than dorsal valve in both lateral and anterior views; mean hinge line ~ 32 mm; anterior commissure uniplicate and slightly modified by lateral plicae; delthyrium relatively high and triangular, not covered; ventral median sulcus narrow and shallow; ventral surface mostly abrased, but traces of low, wide plicae observed with widely spaced grooves or interspaces; fine, closely spaced, concentric growth lines nearby anterior margin; dorsal beak short; dorsal fold moderately high, originating from beak, gradually widening toward anterior margin, with sulcate groove, increasing steadily in width anteriorly, with five or six plicae on each side; weak, low, concentric growth lamellae or growth lines developed; ventral interior with large teeth and large dental plates; adductor scars long and narrow; diductor scars striated; dorsal interior with median septum and large, strong dental socket.

Materials

A total of 21 specimens: two dorsal valves and 19 articulated shells.

Remarks

The current species was first named by Kotlyar in Reference Kotlyar and Popeko1978 as Tomiopsis atlanichus from the lower Permian of southern Primorye, Russian Far East. Then, Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991) revised the generic name of the species to Ingelarella based on the collections from southeast Mongolia and made a brief description and comparison of it. Our collections are also from southeastern Mongolia, and from approximately the same stratigraphical position in the Hovsugol Horizon. The type species Ingelarella angulata (see Campbell, Reference Campbell1959, p. 345, pl. 56, fig. 4a–c, pl. 57, figs. 1–5) from the lower to middle Permian of the Ingelara Shale, Queensland, Australia differs from Ingelarella atlanicha by its fewer, coarser lateral plicae. Ingelarella magna Campbell, Reference Campbell1960 (p. 1117, pl. 140, figs. 1–4), also from the Permian of Queensland, Australia, is distinguished by its larger size (largest 100 mm wide and 85 mm long), shallower ventral sulcus, and lower but much broader plicae. Ingelarella xizangensis Zhan and Wu, Reference Zhan and Wu1982 (p. 99, pl. 5, figs. 5–11) from the lower to middle Permian of Xainza District, Xizang (Tibet), China differs from the present species in having valves of equal convexity, faint plicae, and a much lower ventral interarea. Ingelarella atlanicha differs from the Ingelarella sp. indet. described by Lee et al. (Reference Lee, Shi, Runnegar and Waterhouse2023) from the Kungurian Snapper Point Formation (southern Sydney Basin) in having a more strongly convex shell profile, a deeper ventral sulcus, and more numerous shell plicae.

Ingelarella plana Campbell, Reference Campbell1960

Figure 10.16–10.23

Reference Campbell1960 Ingelarella plana Campbell, p. 1112, pl. 136, figs. 1–7.

Reference Waterhouse1983b Tomiopsis plana; Waterhouse, p. 159, pl. 2, fig. 10, pl. 3, figs. 1–7.

Reference Begg and Ballard1991 Ingelarella cf. I. plana; Begg and Ballard, p. 149, fig. 8.

Holotype

An internal mold of a ventral valve from Springsure shelf and Bowen Basin, eastern Australia (Campbell, Reference Campbell1960, p. 1112, pl. 136, fig. 6a–c).

Occurrence

HV-4, 5, 9; Hovsugol, Mongolia; late Cisuralian.

Description

Relatively large; wider than long, width approximately two-thirds of length; transverse shell, ovally pentagonal in outline; widest part along hinge line or slightly anteriorly; ventral valve low in convexity in both lateral and anterior profiles; cardinal extremities subrounded; anterior commissure uniplicate; ventral beak not well preserved; median sulcus shallow, wide, originating from umbo, gradually widening toward anterior margin, but still shallow in depth with rounded floor, producing slightly high, flattened tongue anteriorly; ventral surface with low, broad plicae, approximately three very broad, rounded low plicae on each side of median sulcus; interspaces between these weak plicae shallow, wide, with rounded floors; ventral interior with long, relatively narrow adductor scars and wide, striated diductor scars.

Materials

Two ventral valves and one ventral valve with internal structure.

Remarks

The specimens described here correspond well with the original description and illustrations of Ingelarella plana by Campbell (Reference Campbell1960, p. 1112, pl. 136, figs. 1–7). According to the description and figures of Waterhouse (Reference Waterhouse1983a), Tomiopsis plana is considered to be Ingelarella plana in this study. Compared to Ingelarella atlanicha described above, Ingelarella plana is larger with lower convexity and a shallower ventral sulcus. Ingelarella costata Waterhouse, Reference Waterhouse1964 (p. 159, pl. 31, figs. 6, 9–15, pl. 32, figs. 1–3, pl. 35, figs. 2, 3, text-figs. 75, 76) from the lower to middle Permian of New Zealand bears some resemblance to the present species in having only a few plicae and a broad sulcus, but it differs from the latter by its smaller size, higher plicae, and V-shaped median sulcus in cross section. Ingelarella sp. indet. from southern Sydney Basin (Lee et al., Reference Lee, Shi, Runnegar and Waterhouse2023) is similar to Ingelarella plana in outline and profile, but the latter has a wider ventral sulcus and weaker shell plicae.

Superfamily Spiriferoidea King, Reference King1846

Family Spiriferoidea Schuchert, Reference Schuchert1893

Genus Neospirifer Fredericks, Reference Fredericks1924

Type species

Spirifer fasciger Keyserling, Reference Keyserling, Von Krusenstern and Keyserling1846 (p. 231, pl. 8, figs. 3–3b) from the upper part of lower Permian of southern Timan, Troitsko-Pechora District (right bank of the Soiva River, 7.5 km upriver from the village of Bol’shaya Soivinskaya), Russia.

Neospirifer koargychanensis Zavodowsky in Zavodowsky and Stepanov, Reference Zavodowsky, Stepanov and Kulikov1971

Figure 11.1–11.11

Figure 11.

Brachiopods from Hovsugol, southeastern Mongolia. (1–11) Neospirifer koargychanensis Zavodowsky, Reference Zavodowsky, Stepanov and Kulikov1971: ventral (1), dorsal (2), anterior (3), and posterior (4) views of an incomplete articulated shell from bed 8; ventral (5), dorsal (6), anterior (7), posterior (8), and lateral (9) views of an articulated shell from bed 13; and dorsal (10) and posterior (11) views of a dorsal valve from bed 14 (NIGP 208995–208997). (12–19) Spiriferella ovata Lee and Gu, Reference Lee and Gu1976: ventral (12), dorsal (13), anterior (14), posterior (15), and lateral (16) views of an incomplete articulated shell; ventral view (17) of a ventral valve; dorsal view (18) of a dorsal valve; and ventral view (19) of a ventral valve with internal structure, all from bed 5 (NIGP 208998–209001). (20–24) Spiriferella keilhaviiformis Fredericks, Reference Fredericks1916: ventral (20), dorsal (21), anterior (22), posterior (23), and lateral (24) views of an articulated shell from bed 14 (NIGP 209002). ads = adductor scars; dds = diductor scars; dp = dental plates; mr = median ridge.

Reference Zavodowsky, Stepanov and Kulikov1971 Neospirifer koargychanensis Zavodowsky in Zavodowsky and Stepanov, p. 155, pl. 31, fig. 3, pl. 32, figs. 1, 2.

Reference Abramov and Grigorjewa1988 Crassispirifer koargychanensis; Abramov and Grigorjewa, p. 168, pl. 23, figs. 2, 3, pl. 24, fig. 1.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Neospirifer koargychanensis; Pavlova et al., p. 129, pl. 29, figs. 2, 3.

Holotype

An articulated shell from Omolon River Basin in northeastern USSR (Zavodowsky and Stepanov, Reference Zavodowsky, Stepanov and Kulikov1971, p. 155, pl. 31, fig. 3).

Occurrence

HV-5, 6, 8, 13–15; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; maximum shell length in present study ~ 45 mm, maximum width ~ 71 mm; broadly transverse and regularly to irregularly semielliptical in outline; widest part at hinge line, alate; slightly dorsobiconvex; anterior commissure uniplicate, but plicated laterally; ventral beak short, somewhat hooked and hanging over hinge line; delthyrium widely wedge-shaped; pseudodeltidium not preserved; median sulcus shallow to moderately deep, broad, bounded by crests of coarse costae; median trough U-shaped in cross section; surface costate, costae strongly fasciculate, four or five fascicles forming plications and becoming lower laterally on each side of sulcus; each fascicle with high primary costa forming crest of plication, height slightly increasing anteriorly; costae 3–5 per fascicle; dorsal fold high and strong, beginning from beak, narrow, low; dorsal surface costae and fascicles similar to those on ventral valve, but fascicles slightly lower with wider interspaces; interior unknown.

Materials

A total of 41 specimens: 23 ventral valves, 14 dorsal valves, and four articulated shells.

Remarks

Neospirifer koargychanensis was named by Zavodowsky in Zavodowsky and Stepanov Reference Zavodowsky, Stepanov and Kulikov1971 and collected from the Cisuralian fauna of the Omolon River Basin in the northeastern USSR. Abramov and Grigorjewa (Reference Abramov and Grigorjewa1988, p. 168) considered the current species to belong to the genus Crassispirifer Archbold and Thomas, Reference Archbold and Thomas1985, but as pointed out by Archbold and Thomas (Reference Archbold and Thomas1985), the costae of Crassispirifer are coarser than those of Neospirifer. Thus, Abramov and Grigorjewa’s species from the Permian of the Verkhoyan area are still treated as Neospirifer rather than Crassispirifer. One of the close species mentioned by Zavodowsky in Zavodowsky and Stepanov Reference Zavodowsky, Stepanov and Kulikov1971 is Neospirifer kedonensis (see Einor in Kaschirzev, Reference Kaschirzev1959, p. 56, pl. 23, figs. 1–4; Zavodowsky and Stepanov, Reference Zavodowsky, Stepanov and Kulikov1971, pl. 74, figs. 1, 2) from the Kazanian Omolon Horizon of northeastern Siberia, but Neospirifer koargychanensis differs in having a deeper and narrower median sulcus, thinner costae, and a higher dorsal umbonal area. Neospirifer sulcoprofundus Liu and Waterhouse, Reference Liu and Waterhouse1985 (p. 35, pl. 9, figs. 5, 8, 11, pl. 10, figs. 2, 3, 6, 8, pl. 11, figs. 2, 3, 5, 6, 9, pl. 12, figs. 1, 3) from the lower to middle Permian of Xiujimqinqi region, Neimongol (Inner Mongolia), northern China is distinguished by its more triangular outline, coarser costae, and weaker fasciculation.

Family Spiriferellidae Waterhouse, Reference Waterhouse1968a

Genus Spiriferella Tschernyschew, Reference Tschernyschew1902

Type species

Spirifer saranae de Verneuil, Reference de Verneuil, Murchison, Verneuil and Keyserling1845 (p. 169, pl. 6, fig. 15a, b) from the lower Permian of the Sakmarian beds in the Sarana River, south of Krasnoufimsk, the Urals, Russia.

Spiriferella ovata Lee and Gu, Reference Lee and Gu1976

Figure 11.12–11.19

Reference Lee and Gu1976 Spiriferella ovata Lee and Gu, p. 294, pl. 171, figs. 7, 8, 11.

Reference Lee, Gu and Su1980 Spiriferella ovata; Lee et al., p. 419, pl. 179, figs. 13, 15, 16.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Spiriferella ovata; Pavlova et al., p. 124, pl. 30, figs. 1–4, pl. 31, figs. 4–6.

Reference Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Spiriferella ovata; Afanasjeva et al., p. 147, pl. 58, figs. 3–5.

Holotype

An articulated shell from Inner Mongolia, China (Lee and Gu, Reference Lee and Gu1976, p. 294, pl. 171, figs. 7, 8, 11).

Occurrence

HV-5–8, 11, 13, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; longitudinally subovate or ovate in outline, the widest part around midlength or slightly anterior; pronounced ventribiconvex; hinge approximately two-thirds of shell width; ventral beak prominent, strongly incurved, protruding beyond hinge line, tip pointed; delthyrium high and triangular in shape; median sulcus well defined by two broadly high plications, originating from beak, narrow and deep at posterior part, but gradually widening and deepening to anterior margin, nearly half of shell width at anterior margin, with median trough U-shaped (or flatly V-shaped) in cross section; surface strongly costate, broadly rounded, beginning at beak, each costa generally bifurcating and producing very weak fascicles, making distinct plications of shell; growth lines and laminae very weak; dorsal beak short and blunt; interarea very low and wide; surface ornamentation similar to that of ventral valve, but with lower and wider plications; ventral interior with strong dental plates, strongly thickened posteriorly; muscle field elongate to spoon-shaped, bisected by very low median ridge; adductor scars narrow and slightly raised, diductor scars larger; dorsal interior unknown.

Materials

A total of 142 specimens: 129 ventral valves, one internal mold of ventral valve, one external mold of ventral valve, five ventral valves with internal structure, four dorsal valves, and two articulated shells.

Remarks

This species was proposed by Lee and Gu (Reference Lee and Gu1976) from the Zhesi Formation (approximately Roadian to Wordian age) of Inner Mongolia, China. The characteristics of the species are its large size, longitudinally ovate outline, and bifurcating costae appearing as low fascicles. The Mongolian specimens, studied herein, are slightly smaller than the type specimens illustrated by Lee and Gu (Reference Lee and Gu1976), however, all features fully agree with the descriptions and illustrations presented by Lee and Gu (Reference Lee and Gu1976). The Mongolian specimens are also similar to those illustrated by Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991) and Afanasjeva et al. (Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003); in both instances, the specimens were collected from near the same area of the Hovsugol region in southeastern Mongolia. As mentioned by Lee and Gu (Reference Lee and Gu1976, p. 294) and Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991, p. 125), Spiriferella ovata resembles Spiriferella rajah, but differs from the latter by its longitudinally ovate outline, fewer lateral plications, and shorter hinge line. Spiriferella primaeva Waterhouse and Waddington, Reference Waterhouse and Waddington1982 (p. 12, pl. 1, figs. 1–6, text-fig. 10) from the Carboniferous of the Yukon Territory and the Canadian Arctic Archipelago is readily distinguished from the current species by its much wider, simple plications and rare or no costae.

Spiriferella keilhaviiformis Fredericks, Reference Fredericks1916

Figures 11.20–11.24, 12.1–12.6

Figure 12.

Brachiopods from Hovsugol, southeastern Mongolia. (1–6) Spiriferella keilhaviiformis Fredericks, Reference Fredericks1916: ventral (1), dorsal (2), anterior (3), posterior (4), and lateral (5) views of an articulated shell from bed 5; and ventral view (6) of a ventral valve with internal structure from bed 5 (NIGP 209003, 209004). (7–16) Spiriferella mugunica Pavlova in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991: ventral (7, 12), dorsal (8, 13), anterior (9, 14), posterior (10, 15), and lateral (11, 16) views of two articulated shells from bed 15 and bed 16 (NIGP 209005, 209006). (17–22) Spiriferella keilhavii (von Buch, Reference von Buch1847): ventral (17), dorsal (18), anterior (19), posterior (20), and lateral (21) views of an articulated shell; and dorsal view (22) of an internal mold of a dorsal valve, both from bed 5 (NIGP 209007, 209008). (23–29) Spiriferella praesaranae (Stepanov, Reference Stepanov1948): ventral (23, 26), posterior (24, 27), and lateral (25, 28) views of two ventral valves from bed 6 and bed 5; and ventral view (29) of a ventral valve with internal structure from bed 5 (NIGP 209009–209011). dds = diductor scars.

Reference Fredericks1916 Spiriferella rajah var. keilhaviiformis Fredericks, p. 85, pl. 5, fig. 7.

Reference Grabau1931 Spiriferella keilhaviiformis; Grabau, p. 160, pl. 21, figs. 6, 7.

Reference Lee, Gu and Su1980 Spiriferella keilhaviiformis; Lee et al., p. 419, pl. 178, figs. 11, 12.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Spiriferella keilhaviiformis; Pavlova et al., p. 126, pl. 30, fig. 8.

Holotype

A ventral shell from Inner Mongolia, China (Fredericks, Reference Fredericks1916, p. 85, pl. 5, fig. 7).

Occurrence

HV-5–9, 12–16; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized; slightly wider than long; transversely ovate in outline, widest part around midlength; pronounced ventribiconvex; anterior commissure uniplicate, weakly plicated laterally; ventral beak prominent, strongly hooked, slightly protruding beyond hinge line with pointed tip; interarea moderately high, weakly concave, narrow at beak, rapidly widening anteriorly; delthyrium high and triangular; median sulcus relatively shallow, defined by two broadly high plications, originating from beak, narrow, moderately deep at posterior part, then gradually widening and deepening to the anterior margin, broadly rounded on floor; surface moderately to strongly costate; costae broad, rounded, beginning at beak, each costa generally bifurcating once and producing very weak fascicles, making low plications on shell; each flank bearing four or five plications, plications moderately high with rounded crests, separated by shallow, narrow, rounded interspaces; growth lines weak with some small pustules on surface; dorsal fold moderately high, strong, gradually widening toward anterior margin; surface ornamentation similar to that of ventral valve, but with slightly lower, wider plications; ventral interior with strong, relatively short dental plates; muscle field broad; adductors depressed, diductors striated longitudinally; dorsal interior unknown.

Materials

A total of 408 specimens: 348 ventral valves, one external mold of ventral valve, 45 ventral valves with internal structure, seven dorsal valves, one dorsal valve with internal structure, and six articulated shells.

Remarks

The specimen illustrated by Fredericks (Reference Fredericks1916, p. 85, pl. 5, fig. 7) as Spiriferella rajah var. keilhaviiformis Fredericks, Reference Fredericks1916 is relatively larger than the specimens studied herein, with more pronounced costae and plications. But the simple bifurcating costae are the same as those on the specimens described herein. Grabau (Reference Grabau1931, p. 160, pl. 21, figs. 6, 7) provided two fragmented specimens of the species Spiriferella keilhaviiformis from the Guadalupian of Jisu Honguer (Zhesi), Inner Mongolia, which are also larger, but have the same surface costae and plications as the material studied. Moreover, our specimens fully agree with the specimen illustrated by Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991, p. 126, pl. 30, fig. 8) from southern Mongolia. The species of Spiriferella keilhavii described by Harker and Thorsteinsson (Reference Harker and Thorsteinsson1960, p. 72, pl. 22, figs. 9–11, pl. 23, figs. 1, 2) from the Assistance Formation of Grinnell Peninsula, Arctic Archipelago, bears some resemblance to Spiriferella keilhaviiformis, however, the former differs from the latter by having a higher interarea, the widest part of the shell along the hinge, and a somewhat V-shaped ventral sulcus in cross section. Spiriferella wangi Liu and Waterhouse, Reference Liu and Waterhouse1985 (p. 31, pl. 7, fig. 9, pl. 8, figs. 1–5, 7, 8) from the Houtoumiao Formation (possible Artinskian age) of Inner Mongolia, China differs from Spiriferella keilhaviiformis by its elongate outline, simple plicae, and narrow sulcus.

Spiriferella mugunica Pavlova in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991

Figure 12.7–12.16

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Spiriferella mugunica Pavlova in Pavlova et al., p. 127, pl. 30, figs. 5–7.

Holotype

An articulated shell from southern Mongolia (Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991, p. 127, pl. 30, fig. 5a, b).

Occurrence

HV-5, 7, 13–15; Hovsugol, Mongolia; late Cisuralian.

Description

Small; transversely semicircular to subcircular in outline, the widest part around the midlength or slightly posteriorly, rarely at hinge line; pronounced ventribiconvex; ventral beak short, strongly incurved but not protruding beyond hinge line; interarea moderately high, concave, narrow at beak; delthyrium moderately high, triangular; median sulcus originating from beak, narrow and shallow at posterior part, gradually widening and deepening to the anterior margin; surface strongly costate; costae broadly rounded, each costa weakly bifurcating once and producing very weak fascicles, but making distinct plications on shell; interspaces between plications rounded, shallow, moderately wide; each flank bearing four or five pairs of plicae, low and broad, well rounded; the innermost pairs (those close to sulcus) normally higher and wider than any other pairs; growth lines and laminae very weak over anterior half of shell; dorsal fold typically low and well demarcated from flanks by lateral grooves, crest divided by a thin median groove beginning from umbo or anterior to umbo; flanks normally covered with three or four pairs of plicae, plicae separated by wide, shallow interspaces; weak growth lines and thin laminae observed on the anterior margin of shell; ventral interior elongate with small muscle field; adductor scars narrow and elongate, diductor scars striated.

Materials

A total of 32 specimens: 24 ventral valves, one ventral valve with internal structure, two dorsal valves, and five articulated shells.

Remarks

Until this study, Spiriferella mugunica has only been reported from the middle to upper Permian of southern Mongolia by Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991). However, the current study suggests that this species is in the lower Permian of southeastern Mongolia. Our specimens agree with or are comparable with Pavlova’s illustrations (Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991, p. 127, pl. 30, figs. 5–7). One of the closest species to the present species is Spiriferella talbeica Ifanova, Reference Ifanova, Ifanova and Semenova1972 (p. 140, pl. 13, figs. 3, 4) from the Permian deposit (possible Kungurian age) of the Petchora Basin in Russia. However, Spiriferella talbeica differs from Spiriferella mugunica by its deeper and wider median sulcus, more lateral plicae, and more elongate shell outline. The species Spiriferella draschei (Toula, Reference Toula1875) described by Cooper (Reference Cooper1957, p. 56, pl. 11C. figs. 7–20) from the Permian of central Oregon differs from Spiriferella mugunica by its larger size, its wider median sulcus, and by having more costae and plicae.

Spiriferella keilhavii (von Buch, Reference von Buch1847)

Figure 12.17–12.22

Reference von Buch1847 Spirifer keilhavii von Buch, p. 74, pl. 1, fig. 2a, b.

Reference Salter1855 Spirifer keilhavii; Salter, p. 386, pl. 36, figs. 9–11.

Reference Frech and Von Roemer1901 Spirifer keilhavii; Frech, pl. 57c, fig. 1b, c.

Reference Tschernyschew1902 Spiriferina (Spiriferella) keilhavii; Tschernyschew, p. 126, 527, pl. 40, figs. 1–4.

Reference Wiman1914 Spiriferina keilhavii; Wiman, p. 36, pl. 2, figs. 25–30, pl. 3, fig. 1.

Reference Tschernyschew and Stepanov1916 Spiriferella keilhavii; Tschernyschew and Stepanov, p. 79, pl. 11, figs. 2, 3.

Reference Frebold1931 Spiriferella keilhavii; Frebold, p. 28, pl. 5, figs. 7–9.

Reference Grabau1931 Spiriferella keilhavii; Grabau, p. 164, pl. 20, fig. 9a–c, pl. 21, figs. 1–5.

Reference Stepanov1936 Spiriferella keilhavii; Stepanov, p. 123, pl. 5, figs. 2, 3.

Reference Frebold1937 Spiriferella keilhavii; Frebold, p. 46, pl. 11, fig. 9.

Reference Stepanov1937a Spiriferella keilhavii; Stepanov, p. 143, 179, pl. 7, figs. 8–11.

Reference Licharew and Einor1939 Spirifer (Spiriferella) keilhavii; Licharew and Einor, p. 139, pl. 23, figs. 6, 7, pl. 24, figs. 1–9.

Reference Dunbar1955 Spiriferella keilhavii; Dunbar, p. 139, pl. 25, figs. 1–9, pl. 26, figs. 1–11, pl. 27, figs. 1–14.

Reference Harker and Thorsteinsson1960 Spiriferella keilhavii; Harker and Thorsteinsson, p. 72, pl. 22, figs. 9–11, pl. 23, figs. 1, 2.

Reference Yanagida1963 Spiriferella keilhavii; Yanagida, p. 72, pl. 9, figs. 4–9, pl. 10, figs. 1–7.

Reference Gobbett1963 Spiriferella keilhavii; Gobbett, p. 152, pl. 20, figs. 8–10.

Reference Wang, Jin and Fang1964 Spiriferella keilhavii; Wang et al., p. 592, pl. 114, figs. 21–23, pl. 115, fig. 16.

Reference Bamber and Waterhouse1971 Spiriferella aff. S. keilhavii; Bamber and Waterhouse, pl. 20, fig. 7.

Reference Minato, Hunahashi, Watanabe and Kato1979 Spiriferella keilhavii; Minato et al., pl. 67, figs. 1–3.

Reference Tazawa and Gunji1982 Spiriferella keilhavii; Tazawa and Gunji, p. 70, pl. 4, figs. 4–7.

Reference Waterhouse and Waddington1982 Spiriferella keilhavii; Waterhouse and Waddington, p. 28, pl. 4, fig. 15, pl. 6, figs. 3–14, text-figs. 16e, g, h, i, 19.

Reference Tazawa1999 Spiriferella keilhavii; Tazawa, p. 5, pl. 1, figs. 2–6.

Reference Tazawa and Ibaraki2001 Spiriferella keilhavii; Tazawa and Ibaraki, p. 16, pl. 4, figs. 1–10.

Reference Shi, Shen and Tazawa2002a Spiriferella keilhavii; Shi et al., p. 291, fig. 4.16, 4.17.

Holotype

An articulated shell from Svalbard and Jan Mayen (von Buch, Reference von Buch1847, p. 74, pl. 1, fig. 2a, b).

Occurrence

HV-5–8, 13–15; Hovsugol, Mongolia; late Cisuralian.

Description

Large; longitudinally subrectangular in outline, with the greatest width at or near hinge; biconvex shell with ventral valve much more convex than dorsal valve in lateral view; hinge mostly not well or incompletely preserved; ventral beak small, strongly hooked, slightly protruding beyond hinge line; umbo strongly incurved, umbonal angle 60–70º; interarea moderately high, weakly concave; median sulcus wide, moderately deep, with U-shaped cross section and two or three minor costae on each side of inner slopes; sulcal floor with one or two low, weak costae; sulcus originating from umbo, narrow and shallow at posterior part, then gradually widening and deepening to anterior margin, with broadly rounded floor; external surface ornamented by 10–12 strong costae, usually making low plications, and numerous very fine concentric lines; costae broad, rounded, projecting two or three weak fascicles, narrow and moderately deep interspaces between strong costae; dorsal fold moderately wide and low, with a narrow, deep median groove commencing at hinge; external ornament of dorsal valve similar to that of ventral valve, but with relatively simple plicae and broad interspaces; ventral interior with pair of strong dental plates; muscle field large, heart-shaped, slightly elevated anteriorly, tapering with no anterior ridge; adductors long and narrow; diductors wide and weakly striated longitudinally; dorsal interior with small cardinal process and strong sockets.

Materials

A total of 67 specimens: 53 ventral valves, seven ventral valves with internal structure, five dorsal valves, and two articulated shells.

Remarks

As listed above in the synonymy, Spiriferella keilhavii has been commonly described and illustrated. Characteristic features of the species include its large size, widest at the hinge line, and its strongly plicated costae. This species has been reported from the lower to middle Permian of Arctic Canada (Yukon Territory, Devon Island and Ellesmere Island), Canada (British Columbia), USA (Alaska), Greenland, Svalbard (Spitsbergen and Bear Island), North China (Inner Mongolia), northeastern China (Heilongjiang Province), Japan (South Kitakami and Hida Gaien Belts), and Mongolia. The species Spiriferella salteri (see Tschernyschew, Reference Tschernyschew1902, p. 528, pl. 6, fig. 5, pl. 12, figs. 5, 6) from the Cisuralian of the southern Urals and Timan, Russia resembles Spiriferella keilhavii in general outline, but differs from the latter by its higher interarea and deeper ventral sulcus. Spiriferella clypeata Cooper and Grant, Reference Cooper and Grant1976 (p. 2226, pl. 627, figs. 1–22, pl. 628, fig. 37) from the Word Formation of West Texas, USA is distinguished from Spiriferella keilhavii by its lower and broader costae, more auriculate cardinal extremities, and much stronger growth laminae. Spiriferella grandis Kotlyar in Licharew and Kotlyar, Reference Licharew, Kotlyar and Popeko1978 (p. 73, pl. 18, figs. 7, 8) from the Permian of southern Primoria, Russian Far East differs from the present species by its larger size, more transverse outline, and deeper ventral sulcus.

Spiriferella praesaranae (Stepanov, Reference Stepanov1948)

Figure 12.23–12.29

Reference Stepanov1948 Spirifer (Spiriferella) praesaranae Stepanov, p. 43, pl. 10, figs. 3–8.

Reference Mironova1960 Spiriferella praesaranae; Mironova, p. 49, pl. 2, figs. 4–6.

Reference Mironova1967 Spiriferella praesaranae; Mironova, p. 44, pl. 4, fig. 5.

Reference Kalashnikov1980 Spiriferella praesaranae; Kalashnikov, p. 84, pl. 32, figs. 1–4.

Holotype

An incomplete shell from Bashkiria, western Southern Ural Mountains, Russia (Stepanov, Reference Stepanov1948, p. 43, pl. 10, fig. 3).

Occurrence

HV-5–9, 11, 13–15; Hovsugol, Mongolia; late Cisuralian.

Description

Small to medium-sized; transversely ovate to subovate in outline, widest part at hinge or slightly anterior to hinge; biconvex shell with ventral valve more convex than dorsal valve in lateral profile; hinge moderately auriculate, terminating in blunt points in most specimens; anterior commissure uniplicate, gently plicated laterally; sulcus and fold developed; delthyrium high; ventral median sulcus originating from beak, shallow and narrow posteriorly, gradually widening and deepening to anterior margin, well defined by two higher plications, with sulcal floor narrowly rounded and U-shaped in cross section, median sulcus sometimes with very weak costae; external surface with strong, broad, rounded costae, beginning at beaks; dorsal fold low, with narrow, shallow median groove; ventral interior with pair of strong dental plates; muscle area elongate ovate, bisected by thin, low median ridge; adductors elongate and narrow; diductors larger; dorsal interior unknown.

Materials

A total of 163 specimens: 145 ventral valves, one external mold of ventral valve, two ventral valves with internal structure, 11 dorsal valves, and four articulated shells.

Remarks

Spiriferella praesaranae looks very close to Spiriferella kupangensis Beyrich, Reference Beyrich1865 (p. 78, pl. 1, fig. 6a–c) in general outline and shell plications, but it differs from Beyrich’s drawing by its elongate outline, lower convexity of the dorsal valve, and a higher interarea. Spiriferella parva Cooper, Reference Cooper1957 (p. 57, pl. 11A, figs. 1–5) from the Permian of central Oregon, USA resembles Spiriferella praesaranae in shell size, but differs from the latter by its elongate outline, fascicostellate surface, and extremely narrow fold. Spiriferella bitutchensis Abramov, Reference Abramov1974 (p. 86, pl. 3, figs. 9, 10) from the Cisuralian deposits of the southern Verkhoyansk Region is similar to Spiriferella praesaranae in its transverse shell outline, but it differs from the latter by its very coarse plications and wider interspaces.

Genus Alispiriferella Waterhouse and Waddington, Reference Waterhouse and Waddington1982

Type species

Spirifer (Spiriferella) keilhavii var. ordinaria Einor in Licharew and Einor, Reference Licharew and Einor1939 (p. 140, pl. 23, figs. 6, 7, pl. 24, fig. 1) from the Cisuralian of Novaya Zemlya in Russia.

Alispiriferella lita (Fredericks, Reference Fredericks1924)

Figure 13.1–13.8

Figure 13.

Brachiopods from Hovsugol, southeastern Mongolia. (1–8) Alispiriferella lita (Fredericks, Reference Fredericks1924): ventral (1), dorsal (2), posterior (3), and lateral (4) views of an articulated shell from bed 15; and ventral (5), posterior (6), lateral (7), and dorsal (8) views of a ventral valve from bed 5 (NIGP 209012, 209013). (9–16) Paeckelmanella latissima Pavlova in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991: ventral (9), dorsal (10), anterior (11), and posterior (12) views of an incomplete articulated shell from bed 8; ventral (13) and posterior (14) views of a ventral valve from bed 9; and dorsal (15) and posterior (16) views of a dorsal valve from bed 8 (NIGP 209014–209016). (17–20) Paeckelmanella expansa (Tschernyschew, Reference Tschernyschew1902): ventral (17), dorsal (18), anterior (19), and posterior (20) views of an incomplete articulated shell from bed 14 (NIGP 209017). (21–25) Phricodothyris suborbicularis (Reed, Reference Reed1944): ventral (21), dorsal (22), anterior (23), posterior (24), and lateral (25) views of an incomplete articulated shell from bed 7 (NIGP 209018). dp = dental plates.

Reference Fredericks1924 Spiriferella saranae mut. lita Fredericks, p. 36, pl. 1, figs. 16–27, text-fig. 2a, b.

Reference Hayasaka1925 Spirifer cf. S. saranae mut. lita; Hayasaka, p. 98, pl. 5, fig. 14.

Reference Stepanov1937b Spiriferella lita; Stepanov, p. 32, pl. 1, fig. 11, pl. 2, figs. 10, 11, pl. 5, fig. 5, pl. 11, fig. 1.

Reference Nonaka1944 Spiriferella cf. S. saranae mut. lita; Nonaka, p. 86, pl. 7, figs. 12–14.

Reference Ustritsky and Tschernjak1963 Spiriferella lita; Ustritsky and Tschernjak, p. 109, pl. 36, figs. 8, 9.

Reference Tazawa1979 Spiriferella lita; Tazawa, p. 28, pl. 4, figs. 12, 13, pl. 5, figs. 1–4, 6.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Alispiriferella lita; Pavlova et al., p. 128, pl. 30, figs. 9, 10, 15.

Reference Tazawa, Takizawa and Kamada2000 Spiriferella cf. S. lita; Tazawa et al., p. 12, pl. 1, figs. 16, 17.

Reference Tazawa2001a Alispiriferella japonica Tazawa, p. 303, fig. 8.15–8.18.

Reference Tazawa2001b Spiriferella lita; Tazawa, p. 302, fig. 8.19–8.22.

Reference Tazawa and Chen2006 Spiriferella lita; Tazawa and Chen, p. 336, fig. 6.4.

Reference Tazawa and Hasegawa2007 Alispiriferella lita; Tazawa and Hasegawa, p. 9, fig. 5.3–5.11.

Reference Tazawa2008a Alispiriferella lita; Tazawa, p. 41, fig. 6.6, 6.7.

Reference Tazawa2008b Alispiriferella lita; Tazawa, p. 55, fig. 9.8a–9.14.

Reference Tazawa2009 Alispiriferella lita; Tazawa, p. 74, fig. 5.4a–5.9.

Holotype

An incomplete ventral valve from Ussuri, South Primorye, Russia (Fredericks, Reference Fredericks1924, p. 36, pl. 1, fig. 19).

Occurrence

HV-5, 8, 13–15; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; transversely subovate in outline, greatest width variably placed between hinge and midlength; pronounced ventribiconvex; anterior commissure broadly uniplicate; ventral beak small, strongly incurved, hanging over hinge line; interarea moderately high, broad, gently concave, with large delthyrium; median sulcus narrow and moderately deep on posterior half, then widening and deepening toward anterior margin with broad V-shaped tongue protruding dorsally, with one or two pairs of weak costae; external surface strongly costate, three or four pairs of strong, simple, high, sharp or broad-crested plicae on each side of sulcus; dorsal fold relatively high and wide, steep-sided anteriorly, with narrow and deep median groove for almost entire length; dorsal external ornament similar to that of ventral valve, but with relatively narrower plicae and wider interspaces; ventral interior with pair of high dental plates; muscle field deeply impressed and heart-shaped; dorsal interior unknown.

Materials

A total of 36 specimens: 24 ventral valves, three internal molds of ventral valves, one external mold of ventral valve, two dorsal valves, one dorsal valve with internal structure, and five articulated shells.

Remarks

This species was originally reported from the middle Permian of Ussuri, South Primorye, Russia by Fredericks in 1924. Our specimens are assigned to Alispiriferella lita on the basis of their relatively large and transverse shells, strong and simple external costae, and the presence of a V-shaped ventral sulcus in cross section. Alispiriferella lita has been reported mostly from the middle to upper Permian of East Asia as listed by Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991, p. 129) and Tazawa (Reference Tazawa2009, p. 75), however, our new collections from southeastern Mongolia appear to extend the stratigraphical position of the species to the Kungurian. The type species of Alispiriferella, Alispiriferella ordinaria can be distinguished from Alispiriferella lita by its smaller shell size, a ventral sulcus with two prominent sulcal costae, and a somewhat less transverse outline. Alispiriferella sinensis Wang and Zhang, Reference Wang and Zhang2003 (p. 154, pl. 43, figs. 9, 10, pl. 46, figs. 1–8) from the Guadalupian of Zhesi Section of Inner Mongolia resembles Alispiriferella lita in its external shell surface, but differs from the latter by its rhomboid outline, slightly rounded cardinal extremities, and prominent concentric growth lines along the anterior margins of both valves.

Superfamily Paeckelmanelloidea Ifanova, Reference Ifanova, Ifanova and Semenova1972

Family Paeckelmanellidae Ifanova, Reference Ifanova, Ifanova and Semenova1972

Subfamily Paeckelmanellinae Ifanova, Reference Ifanova, Ifanova and Semenova1972

Genus Paeckelmanella Licharew, Reference Licharew1934

Type species

Spirifer dieneri Tschernyschew, Reference Tschernyschew1902 (p. 535, pl. 9, figs. 6–8) from the lower Permian (Schwagerina Limestone) of the Ural Mountains, Russia.

Paeckelmanella latissima Pavlova in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991

Figure 13.9–13.16

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Paeckelmanella latissima Pavlova in Pavlova et al., p. 137, pl. 32, fig. 4.

Reference Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Paeckelmanella latissima; Afanasjeva et al., p. 153, pl. 60, fig. 10.

Holotype

An articulated shell from Hovsugol area, Mongolia (Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991, p. 137, pl. 32, fig. 4).

Occurrence

HV-4–9, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized to large; much wider than long; transversely triangular to subtriangular in outline, with greatest width along hinge line; low biconvexity, ventral valve more convex than dorsal valve in lateral profile, usually longitudinal convexity of each valve is greater than transverse convexity; anterior commissure slightly uniplicate and often crushed; ventral delthyrium narrowly triangular; median sulcus moderately deep, beginning from beak, relatively narrow and shallow, then gradually widening a little toward anterior margin, U-shaped trough in cross section; median costa on sulcus weakly developed; external costae simple, low and broad, amplitude decreasing distally, 6–9 pairs on each side of median sulcus; interspaces of costae narrow and shallow; fine concentric growth lines or lamellae observed near anterior margin on some specimens; dorsal fold relatively high and narrow; interior unknown.

Materials

A total of 36 specimens: 18 ventral valves, two external molds of ventral valves, 10 dorsal valves, one internal mold of dorsal valve, four external molds of dorsal valves, and one incomplete articulated shell.

Remarks

Paeckelmanella latissima was established by Pavlova (in Pavlova et al., Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991) from the Hovsugol area of southern Mongolia. Our specimens are generally the same as those Pavlova described and illustrated. Paeckelmanella ulanensis Lee and Gu, Reference Lee and Gu1976 (p. 279, pl. 176, fig. 8) from the Zhesi Formation of Inner Mongolia differs from the current species by its fewer surface costae that are much wider and higher. However, Lee and Gu’s specimen is not well preserved, and the description provided by them is very brief and unclear and requires revision. Wang and Zhang (Reference Wang and Zhang2003, p. 166) commented that the species either named or described by Lee and Gu are possibly not Paeckelmanella but might belong to other genera. However, because of the poor preservation of their specimens, further identification of the species described by Lee and Gu (Reference Lee and Gu1976) is hindered. Paeckelmanella muliplicata Gu and Zhu, Reference Gu and Zhu1985 (p. 89, pl. 2, fig. 17) from the lower Permian of Lindong area in Inner Mongolia is similar to the present species in general outline but differs from the latter by its extremely high ratio of width to length.

Paeckelmanella expansa (Tschernyschew, Reference Tschernyschew1902)

Figure 13.17–13.20

Reference Tschernyschew1902 Spiriferina expansa Tschernyschew, p. 518, pl. 12, fig. 11, pl. 14, figs. 6, 7, pl. 40, fig. 8.

Reference Licharew and Licharew1939a Spirifer (Paeckelmanella?) expansa; Licharew, p. 109, pl. 27, fig. 4.

Reference Licharew and Gorsky1939b Spirifer (Paeckelmanella) expansa; Licharew, p. 117, pl. 20, fig. 4.

Reference Gobbett1963 Paeckelmanella aff. P. expansa; Gobbett, p. 156, pl. 21, figs. 1–3, text-fig. 22.

Reference Zavodowsky, Stepanov and Kulikov1971 Paeckelmanella expansa; Zavodowsky and Stepanov, p. 109, pl. 12, figs. 6–8, pl. 29, figs. 10, 11, pl. 33, fig. 11.

Reference Ifanova, Ifanova and Semenova1972 Paeckelmanella expansa; Ifanova, p. 132, pl. 9, fig. 10.

Reference Kulikov1974 Spiriferinaella expansa; Kulikov, p. 101, pl. 7, fig. 4.

Reference Kalashnikov1980 Paeckelmanella expansa; Kalashnikov, p. 76, pl. 21, fig. 5.

Reference Ivanova1981 Paeckelmanella expansa; Ivanova, p. 37, pl. 6, figs. 1–3.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Paeckelmanella expansa; Pavlova et al., p. 138, pl. 32, figs. 5, 6.

Reference Kalashnikov1998 Paeckelmanella expansa; Kalashnikov, p. 67, pl. 32, fig. 3.

Reference Wang and Zhang2003 Paeckelmanella expansa; Wang and Zhang, p. 166, pl. 45, figs. 1–3.

Holotype

A ventral valve from Ural Mountains, Russia (Tschernyschew, Reference Tschernyschew1902, p. 518, pl. 12, fig. 11).

Occurrence

HV-5, 7, 8, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized; strongly transverse, narrowly triangular in outline, with greatest width along hinge line; low biconvexity, ventral valve slightly more convex than dorsal valve in lateral profile; hinge line straight; cardinal extremeties narrowly triangular and pointed; anterior commissure slightly uniplicate; ventral interarea wide, narrow, low, slightly concave; median sulcus beginning from beak or slightly anterior, narrow and shallow, gradually deepening and widening a little toward anterior margin, narrow U-shaped trough in cross section; median costa on sulcus weak; surface costate, two pairs of costae on both sides of median sulcus stronger, making low plications, decreasing distally; six or seven pairs on each side of median sulcus; interspaces of costae moderately wide and shallow; fine concentric growth lines observed on some specimens; dorsal fold narrow and low, originating from beak, gradually widening to anterior margin; external surface similar to that of ventral valve, but costae lower and tending to be smooth close to cardinal extremities; interior unknown.

Materials

A total of 27 specimens: 15 ventral valves, one external mold of ventral valve, eight dorsal valves, and three incomplete articulated shells.

Remarks

The current species is one of the most frequently described species in the genus Paeckelmanella, as evidenced by the above synonymy list. The main features of this species are its alate shell with pointed cardinal extremities, low to moderate convexity, and relatively narrow sulcus and fold. Paeckelmanella expansa differs from Paeckelmanella latissima described above by its smaller size, lower convexity, and more elongate rhomboidal outline. Its sulcus is narrower and deeper, clearly bounded by two pairs of low costae, and the median rib along the sulcus axis is more prominent and robust than in Paeckelmanella latissima. Paeckelmanella calignea Stehli and Grant, Reference Grant1971 (p. 515, pl. 65, figs. 1–9, 12–17, 21–24, 29–31, 36) from the Permian of Axel Heiberg Island, Canada is similar in outline to the present species, but differs in having a higher median costa in the sulcus, stronger costae, and a higher dorsal fold.

Suborder Delthyridina Ifanova, Reference Ifanova, Ifanova and Semenova1972

Superfamily Reticularioidea Waagen, Reference Waagen1883 in 1882–1885

Family Elythidae Fredericks, Reference Fredericks1924

Subfamily Phricodothyridinae Caster, Reference Caster1939

Genus Phricodothyris George, Reference George1932

Type species

Phricodothyris lucerna George, Reference George1932 (p. 546, pl. 35, fig. 2a–d) from the lower Carboniferous of Britain.

Remarks

Phricodothyris is small, with a subtransversely ovate outline, double-barrel spines on the concentric lamellae, and spiralia pointed laterally. Permophricodothyris Pavlova, Reference Pavlova1965 is readily distinguished from Phricodothyris by its relatively larger shell, very long and nearly parallel crura, elongate spiralia directed posteriorly with numerous whorls (12–28), and concentric lamellae ornamented with comb-like spines. Squamularia Gemmellaro, Reference Gemmellaro1899 is closer to Phricodothyris in view of its size and spiralia pointed laterally but has comb-like spines on the concentric lamellae and relatively elongate outline and higher interarea. The present specimens have a relatively transverse outline and a less strongly biconvex profile. In the absence of clear evidence for comb-like or uniramous spines on the concentric lamellae due to the poor preservation of the specimens, they are tentatively assigned to Phricodothyris.

Phricodothyris suborbicularis (Reed, Reference Reed1944)

Figures 13.21–13.25, 14.1, 14.2

Figure 14.

Brachiopods from Hovsugol, southeastern Mongolia. (1, 2) Phricodothyris suborbicularis (Reed, Reference Reed1944): ventral view (1) of a ventral valve from bed 5; and dorsal view (2) of an internal mold of a dorsal valve from bed 14 (NIGP 209019, 209020). (3–10) Spirelytha fredericksi Archbold and Thomas, Reference Archbold and Thomas1984: ventral (3, 7), dorsal (4, 8), posterior (5, 9), and lateral (6, 10) views of two incomplete articulated shells from bed 5 and bed 14 (NIGP 209021, 209022). (11–14) Primorewia reshetnikov Licharew and Kotlyar, Reference Licharew, Kotlyar and Popeko1978: ventral (11), anterior (12), and posterior (13) views of an incomplete articulated shell from bed 8; and ventral view (14) of a ventral valve from bed 5 (NIGP 209023, 209024). (15–19) Dielasma cf. D. millepunctatum (Hall, Reference Hall and Humphreys1856): ventral (15), dorsal (16), anterior (17), posterior (18), and lateral (19) views of an articulated shell from bed 5 (NIGP 209025).

Reference Reed1944 Squamularia (Neophricodothyris) baralensis var. suborbicularis Reed, p. 238, pl. 30, figs. 5, 6.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Phricodothyris suborbicularis; Pavlova et al., p. 135, pl. 32, figs. 1, 2.

Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Phricodothyris suborbicularis; Afanasjeva et al., p. 159, pl. 62, figs. 8, 9.

Holotype

Drawing of an articulated shell from Salt Range, Pakistan (Reed, Reference Reed1944, p. 238, pl. 30, figs. 5, 6).

Occurrence

HV-5, 7, 13–15; Hovsugol, Mongolia; late Cisuralian.

Description

Large for genus; wider than long; transversely subcircular or suborbicular in outline, the widest part around midvalve; sides and anterior margin rounded; cardinal extremities rounded; anterior commissure rectimarginate; no sulcus or fold; ventral valve strongly convex in lateral profile and moderately to highly domed in anterior profile; most convex at umbo; beak small and strongly incurved, but not beyond hinge line; palintrope relatively narrow and strongly concave; delthyrium small and triangular; umbonal region strongly inflated, umbonal slopes steep and moderately concave in profile; lateral slopes long and gradually inclining; median sulcus absent; surface mostly smooth on internal molds, some traces of fine concentric lamellae or growth lines can still be observed; some specimens with patches of external surface preserved, with fine and regular concentric lamellae bearing double-barrelled spines on their anterior edges; spine impressions present between lamellae; dorsal valve moderately convex in lateral profile, dorsal convexity greatest slightly anterior to umbo; umbo low, small, moderately inflated; beak short, low, obtusely pointed; umbonal slopes short and gently inclined; no dorsal fold; surface of internal molds of specimens mostly smooth, but with traces of the fine concentric lamellae similar to those on ventral valve; shell worn, internal details unknown.

Materials

A total of 75 specimens: 14 ventral valves, 27 internal molds of ventral valves, 32 internal molds of dorsal valves, and two articulated shells. Registered specimens: one articulated shell (NIGP 139), one ventral valve (NIGP 140), and one internal mold of dorsal valve (NIGP 141).

Remarks

The Mongolian specimens from this collection are very close or identical to the specimens described by Reed (Reference Reed1944, p. 238, pl. 30, figs. 5, 6), who first proposed the species as Squamularia (Neophricodothyris) baralensis var. suborbicularis. The specimens were also described and illustrated by Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991) and Afanasjeva et al. (Reference Afanasjeva, Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003); they are identical to the present specimens because both collections were from the same area of the Hovsugol region. Phricodothyris occidentalis Archbold and Thomas, Reference Archbold and Thomas1984 (p. 323, fig. 4EE–KK) from the lower Permian of Western Australia resembles the present species in its circular shell outline and rectimarginate anterior commissure, but differs in its much smaller size and lower interareas. Phricodothyris lenaensis Abramov and Grigorjewa, Reference Abramov and Grigorjewa1983 (p. 140, pl. 32, figs. 10–12, text-fig. 55) from the middle to upper Carboniferous of Verkhoyan also differs from Phricodothyris suborbicularis by its small size.

Subfamily Toryniferinae Carter, Reference Carter, Carter, Johnson, Gourvennec and Hou1994

Genus Spirelytha Fredericks, Reference Fredericks1924

Type species

Spirelytha pavlovae Archbold and Thomas, Reference Archbold and Thomas1984 (p. 313) for Spirifer scheii Tschernyschew in Tschernyschew and Stepanov, Reference Tschernyschew and Stepanov1916 (p. 45, pl. 9, figs. 5–7) (non Spirifer scheii Meyer, Reference Meyer1913) from the Permian of Arctic Siberia in Russia.

Remarks

Phricodothyris and Spirelytha are morphologically similar. The main distinction between the two lies in the presence of well-developed dental adminicula in the ventral valve of Spirelytha, which are absent in Phricodothyris. In addition, Spirelytha usually has a distinct sulcus on the ventral valve and a relatively high, more rectilinear ventral interarea. Although the internal structures of the specimens described here are unclear, their shell outline and relatively lower ventral interarea suggest greater similarity to Phricodothyris rather than Spirelytha. Therefore, we tentatively assign these specimens to Phricodothyris.

Spirelytha fredericksi Archbold and Thomas, Reference Archbold and Thomas1984

Figure 14.3–14.10

Reference Archbold and Thomas1984 Spirelytha fredericksi Archbold and Thomas, p. 314, figs. 1A–R, 2A–K.

Reference Klets1987 Spirelytha fredericksi; Klets, p. 34, pl. 4, figs. 8–12.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Spirelytha fredericksi; Pavlova et al., p. 134, pl. 31, fig. 7a, b.

Reference Archbold, Thomas, Skwarko and Skwarko1993 Spirelytha fredericksi; Archbold et al., microfilm p. 97, pl. 42, figs. 23–26.

Reference Shi and Waterhouse1996 Spirelytha fredericksi; Shi and Waterhouse, p. 146, pl. 28, figs. 13–21.

Reference Klets2005 Spirelytha fredericksi; Klets, p. 149, pl. 26, figs. 6–11.

Holotype

A complete shell from Callytharra Formation and Fossil Cliff Member, Perth Basin, Western Australia (Archbold and Thomas, Reference Archbold and Thomas1984, p. 313, fig. 1A–R).

Occurrence

HV-5, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized for genus; strongly biconvex, ventral valve slightly more convex than dorsal valve in lateral view; wider than long; shell outline transversely oval; maximum width close to midvalve; hinge line straight, approximately two-thirds of shell width; sides and anterior margin rounded; sulcus and fold weakly developed; delthyrium broad and distinct; surface with concentric lamellae, each lamella bearing a row of biramous spines along anterior edge, one or two in 1 mm; internal structures not well revealed.

Materials

Three articulated shell specimens (NIGP 145, 146).

Remarks

The three specimens described here are not complete; one of them has been deformed on the anterior part of the shell. However, the general outline, surface ornamentation, and weakly developed ventral sulcus and dorsal fold clearly indicate that they are Spirelytha fredericksi. Furthermore, part of the outer layer of the specimens was broken and the patches of the internal molds exposed were the same or nearly identical to the illustrations of Spirelytha fredericksi provided by Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991, p. 134, pl. 31, fig. 7a, b) from the same area of Hovsugol in southeastern Mongolia. The specimens described as Spirelytha fredericksi by Shi and Waterhouse (Reference Shi and Waterhouse1996, p. 146, pl. 28, figs. 13–21) from the Sakmarian of the northern Yukon Territory, Canada are considered to be immature representatives of Spirelytha fredericksi. One of the closest species to the present species is Spirelytha miloradovichi Archbold and Thomas, Reference Archbold and Thomas1984 (p. 318, figs. 2L–Z, AA, BB, 3A–E) from the upper Artinskian to Kungurian of Western Australia, but the latter differs in possessing a higher ventral interarea and more pronounced sulcus and fold.

Order Spiriferinida Ifanova, Reference Ifanova, Ifanova and Semenova1972

Suborder Spiriferinidina Ifanova, Reference Ifanova, Ifanova and Semenova1972

Superfamily Syringothyridoidea Fredericks, Reference Fredericks1926

Family Syringothyrididae Fredericks, Reference Fredericks1926

Subfamily Permasyrinxinae Waterhouse, Reference Waterhouse1986b

Genus Primorewia Licharew and Kotlyar, Reference Licharew, Kotlyar and Popeko1978

Type species

Primorewia reshetnikov Licharew and Kotlyar, Reference Licharew, Kotlyar and Popeko1978 (p. 72, pl. 11, figs. 3–5) from the lower to middle Permian of southern Primoria, Russian Far East.

Remarks

Primorewia and Paeckelmanella share similarities in certain external features as well as in the ventral interior (e.g., divergent dental adminicula). However, Primorewia has a broad and smooth sulcus, and a fold with a distinct median furrow, whereas Paeckelmanella has a median rib in the sulcus, and a smooth and carinate dorsal fold without furrow.

Primorewia reshetnikov Licharew and Kotlyar, Reference Licharew, Kotlyar and Popeko1978

Figure 14.11–14.14

Reference Licharew, Kotlyar and Popeko1978 Primorewia reshetnikov Licharew and Kotlyar, p. 72, pl. 11, figs. 3–5.

Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991 Primorewia reshetnikov; Pavlova et al., p. 133, pl. 31, figs. 1–3.

Reference Afanasjeva, Alekseeva, Grunt, Lazarev and Komarov2003 Primorewia reshetnikov; Afanasjeva et al., p. 151, pl. 60, figs. 1–3.

Holotype

An incomplete ventral valve from Artilleriyskiy key section, Khasansky District, South Primorye, Russia Far East (Licharew and Kotlyar, Reference Licharew, Kotlyar and Popeko1978, p. 72, pl. 11, fig. 4).

Occurrence

HV-5–9, 13, 14; Hovsugol, Mongolia; late Cisuralian.

Description

Large; strongly transverse; transversely triangular in outline, widest part along hinge line; biconvex shell with ventral valve slightly more convex than dorsal valve or nearly equal convexity in lateral view; cardinal extremities triangular, tip narrowly rounded; anterior commissure weakly uniplicate; sulcus and fold moderately developed; delthyrium wide and triangular; surface with simple, low, rounded plicae, 10–13 plicae on each side of median sulcus; interspaces between plicae shallow and narrow with rounded floor; weak concentric growth lines observed; ventral interior with moderate apical callus; relatively strong dental plates and diverging dental adminicula; dorsal interior with strong sockets.

Materials

A total of 35 specimens: 13 ventral valves, one external mold of ventral valve, 11 dorsal valves, three external molds of dorsal valves, and seven articulated shells. Registered specimens: one articulated shell (NIGP 147) and one dorsal valve (NIGP 148).

Remarks

The specimens described under Primorewia reshetnikov are mostly broken and the surface of many of them is somewhat worn, however the general outline and surface ornamentation clearly agrees with those described by Licharew and Kotlyar (Reference Licharew, Kotlyar and Popeko1978) and Pavlova et al. (Reference Pavlova, Manankov, Morozova, Solovieva, Suetenko and Bogoslovskaia1991). This species is the only confirmed species of the genus Primorewia, and the internal structures are not well revealed; further investigations are needed to clarify them.

Order Terebratulida Waagen, Reference Waagen1883 in 1882–1885

Suborder Terebratulidina Waagen, Reference Waagen1883 in 1882–1885

Superfamily Dielasmatoidea Schuchert, Reference Schuchert, von Zittel and Eastman1913

Family Dielasmatidae Schuchert, Reference Schuchert, von Zittel and Eastman1913

Subfamily Dielasmatinae Schuchert, Reference Schuchert, von Zittel and Eastman1913

Genus Dielasma King, Reference King1859

Type species

Terebratulites elongatus von Schlotheim, Reference von Schlotheim1816 (p. 27, pl. 7, fig. 7a–c) from Zechstein Formation, Glücksbrunn, Thuringen, Germany.

Dielasma cf. D. millepunctatum (Hall, Reference Hall and Humphreys1856)

Figure 14.15–14.19

Reference Hall and Humphreys1856 Terebralula millepunclata Hall, p. 101, pl. 1, figs. 1, 2.

Reference Tschernyschew1902 Dielasma millepunctatum; Tschernyschew, p. 456, pl. 3, figs. 2, 4.

Reference Grabau1931 Dielasma millepunctatum var. mongolicum Grabau, p. 57, pl. 4, fig. 5a–d.

Reference Ustritsky and Tschernjak1963 Dielasma cf. D. millepunctatum; Ustritsky and Tshernjak, p. 121, pl. 46, fig. 5.

Occurrence

HV-5; Hovsugol, Mongolia; late Cisuralian.

Description

Medium-sized; subpentagonal in outline, subtriangular in cross section; longer than wide, maximum width at midlength; hinge line strongly curved; cardinal extremities rounded; lateral margins parallel; anterior commissure unplicate; ventral valve flat; median sulcus weak; a broad, gently sinusoidal flattening area across anterior third of length; slight depressions flanking ventral beak; ridge subacute; small pedicle opening; ventral delthyrium fully covered by dorsal umbo; dorsal median fold high, narrow, descending to the lateral margins by steep slopes; profile nearly straight longitudinal; shell surface with weak concentric growth lines; interior unknown.

Materials

One complete shell from the Bed 5 of the Hovsugol section, southern Mongolia (NIGP 87).

Remarks

The specimen described here exhibits closest affinity to Dielasma millepunctatum var. mongolicum, as described by Grabau (Reference Grabau1931, p. 57, pl. 4, fig. 5) from the Enteletes bed of the Permian Jisu Honguer Formation, Mongolia. Shared diagnostic features include a relatively elongate outline, sinusoidal ventral valve flattening, and subtriangular cross-sectional profile. Hall and Clarke (Reference Hall and Clarke1894, pt. 6, v. 8, p. 293, pl. 81, figs. 31, 32) synonymized Dielasma millepunctatum with Dielasma bovidens Morton, Reference Morton1836 (p. 150, pl. 2, fig. 4), but our material diverges markedly from the latter, which displays a pentagonal outline and curved lateral margins. This supports Tschernyschew’s (Reference Tschernyschew1902) interpretation that these taxa represent distinct species. Dielasma plica Kutorga, Reference Kutorga1842 found in the Selander Formation (Permian), Spitsbergen (Wiman, Reference Wiman1914, p. 24, pl. 1, figs. 1–8) shows similarities in shell proportions and longitudinal profile with our specimen, but it differs in possessing a narrow and deep median sulcus, contrasting with the notably shallow sulcus observed here. Given the morphological proximity to Dielasma millepunctatum but limited material (only one specimen), we tentatively assign our specimens to Dielasma cf. D. millepunctatum pending further study.