Preservation and taphonomy

The described fauna is silicified and has been extracted from limestone through etching in acetic acid. The faunal content of the rock is quite rich; brachiopods and gastropods are the most abundant, corals and algae are abundant, echinoderms are frequent, whereas bivalves and ammonoids are rare. The present sample (1791 specimens; see Table 1) has been obtained after dissolving ca. 100 kg of rock; a minor part thereof consists of specimens naturally weathered from the rock.

Table 1

Numerical characteristics of the material studied.

“Total corrected” stands for the sum of articulated shells and of those of either isolated valves which are more numerous; the percentages referred to the “total” (next to last column) are then these in the studied material, whereas those referred to the “total corrected” are an approximation (minimum number of individuals) of the original biocoenosis.

The silicification process does not affect all parts of the shell equally. It was observed that shells of Flabellocyrtia flabellulum and of Thecocyrtella dagysii sometimes possess a deltidium and sometimes not (compare Figs 4.12, 4.24 and 4.14, 4.17, 4.25–4.29, 4.34 as well as 6.1, 6.2, 6.5, 6.7 and 6.3, 6.13, 6.18, 6.32, 6.34–6.37; specimens lacking the deltidium are more frequent). This is best interpreted as resulting from selective silicification; a very similar situation (pseudodeltidium lacking or more seldom present due to selective silicification) was described by Pope (Reference Pope1982, p. 4; see also Holdaway and Clayton, Reference Holdaway and Clayton1982). Hollow spaces appearing inside the shell are also an artifact explained by the silicification either proceeding from the external surfaces towards the internal layers and often remaining incomplete (for an example of a list of artifacts caused by silicification, see Caruthers and Stanley, Reference Caruthers and Stanley2008, p. 155) or occurring preferentially along certain layers of the shell (Crowley, Reference Crowley1988; Carson, Reference Carson1991, p. 462). In some cases, concentric rings (beekite) typical of silicification obscure the original surface of the valves (Fig. 4.31). Although most of original microstructure gets indeed lost during the silicification process (Brenchley and Harper, Reference Brenchley and Harper1998, p. 78), by no means should it be understood that all microstructural information is lost during diagenesis. In several cases, punctae are preserved (Thecocyrtella: Fig. 4.4, Flabellocyrtia: Fig. 4.3, Albasphe: Fig. 4.2) and sometimes the same may be said even about the axial cavity of the spines of the spiralium in Flabellocyrtia. Overall, however, the silicification in the material studied may be described as intermediate in character between two extreme types referred to in a description of silicified Carboniferous brachiopods by Sun and Baliński (Reference Sun and Baliński2008, p. 491), namely preserving very fine details including some information on microstructure on one hand and obliteration of original patterns up to the apparition of a secondary “spongy” texture on another hand.

The percentage of disarticulated valves in the material amounts to about 33% (see Table 1 for details). Referring to a paleoecological analysis of Middle Triassic brachiopod assemblages with different percentages of disarticulated valves (Pálfy, Reference Pálfy1991), the value for Svilaja assemblage corresponds approximately to “reasonable ‘background’ disarticulation under average circumstances,” i.e., without much postmortem transport. However, the ratios of ventral versus dorsal valves are somewhat different from the value 1:1 expected if there is no postmortem bias (Chen et al., Reference Chen, Chen and Tong2010 and references therein). This is especially the case for the spiriferinide Thecocyrtella dagysii in which ventral valves are over eight times more numerous than dorsal ones; this, however, is best explained as expressing their different preservational qualities (Alexander, Reference Alexander1986, Reference Alexander1990)—the ventral valve is massive, whereas the dorsal one is fragile—or perhaps some kind of differential sorting. For the other species the value of the discussed ratio is between 1.26 and 1.46; this seems to indicate a moderate bias. The assemblage is thus interpreted as parautochthonous (perhaps even autochthonous).

The sample is of low diversity (Shannon index=0.88) and relatively medium dominance (Simpson D index=0.54). Rarefaction analysis (Fig. 2) suggests that the present collection is fully saturated and additional sampling is rather unlikely to result in a discovery of additional species. Very small differences between percentages of species referred to the total material and corrected values (minimum number of individuals; Zuschin et al., Reference Zuschin, Stachowitsch and Stanton2003 and references therein) allow to consider that the biocoenosis structure is reflected more or less accurately in the material.

Figure 2

Rarefaction curve for the brachiopod sample from Svilaja.

Remarks

The classification framework and the authorship of the names follow the revised Treatise on Invertebrate Paleontology, Part H (Williams et al. Reference Williams, Carlson and Brunton2000), except for the superfamily Zeillerioidea, the authorship of which is to be attributed to Schuchert (in Schuchert and LeVene, Reference Schuchert and LeVene1929, p. 24) who introduced the subfamily Zeilleriinae by Latinising the vernacular (invalid) name “Zeilleriidés” used by Rollier (Reference Rollier1915). Allan (Reference Allan1940), credited with the authorship in the Treatise, was in fact only the first to use the name at family level. The first use at superfamily level was by Kyansep (Reference Kyansep1961) (personal communication, M. Manceñido, 2014).

Synonymy lists are established with short comments by means of special signs following the system described by Halamski (Reference Halamski2009, p. 46–47; further references therein). For species published in monographs issued during a several years’ period, the full citation follows the model proposed by Halamski and Baliński (Reference Halamski and Baliński2013, p. 265).

Subphylum Rhynchonelliformea Williams et al., Reference Williams, Carlson, Brunton, Holmer and Popov1996

Class Rhynchonellata Williams et al., Reference Williams, Carlson, Brunton, Holmer and Popov1996

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

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

Superfamily Retzioidea Waagen, Reference Waagen1883

Family Neoretziidae Dagys, Reference Dagys1972

Genus Cassianospira Dagys, Reference Dagys1972

Type species

Retzia loczyi Bittner, Reference Bittner1900; Carnian.

Remarks

This genus has been reported from the Upper Triassic (Carnian and Norian) up to now (Dagys, Reference Dagys1974, p. 288; Alvarez and Rong, Reference Álvarez and Rong2002, p. 1591). This is the first report from the Middle Triassic (Ladinian).

Cassianospira humboldtii (von Klipstein, 1845 in 1843–45 [‘1843’])

Figure 3.1–3.16

*1845 Spirifer Humboldtii von Klipstein, p. 233; pl. 15, fig. 17.

1853 Waldheimia? Humboldtii; Gray, p. 85.

1889 Retzia Humboldtii Klipst. sp.; Bittner, p. 168.

1890 Retzia Humboldtii Klipst. spec.; Bittner, p. 88; pl. 2, fig. 33.

Type material

Articulated shell from the Carnian of San Cassian (southern Alps) figured by Klipstein (1845, pl. 15, fig. 17) NHMUK PI OR 30635, holotype by monotypy.

Description

Shell teardrop-shaped, wider than long when young, about as wide as long in larger individuals due to the growth of the ventral umbo, markedly to very strongly ventribiconvex, up to 4.1 mm in width; maximal width about the midlength of the dorsal valve or slightly anteriorly. Hinge line and anterior commissure straight. Ventral valve high; interarea apsacline, nearly flat near the hinge line, markedly incurved in umbonal region; a rather narrow delthyrium closed by a symphytium bordered by low rounded rims (Fig. 3.11); foramen submesothyrid. Dorsal valve weakly convex.

Ornamentation of stout, high, rounded plicae, beginning at umbo, separated by narrower furrows; up to five pairs on the ventral valve, a median one and up to four pairs of lateral ones on the dorsal valve. Growth lines not observed.

Dorsal interior: cardinal flange thick, supported by a high and thin (Fig. 3.10) or moderately thick (Fig. 3.9) median septum, the length of the septum equaling approximately two-thirds of that of the valve; spiralium not preserved. Ventral interior (Fig. 3.7, 3.8) poorly preserved.

Material

Twenty-seven mostly subcomplete articulated shells, four ventral, and three dorsal valves.

Dimensions

ZPAL Bp 72/4/1: length 2.7 mm; width 2.5 mm; thickness 1.8 mm.

Remarks

The publication date of Cassianospira humboldtii requires a comment. The Beiträge zur geologischen Kenntniss der östlichen Alpen by A. v. Klipstein are dated 1843 at the title page (in the reference list of the Treatise on Invertebrate Paleontology, Part H, Revised, confounded with Beiträge zur geologischen und topographischen Kenntnis der östlichen Alpen by the same author printed in three parts between 1871 and 1883). However, “Spirifer humboldtii” (our Cassianospira humboldtii; not to be confounded with Spirifer humboldtii d’Orbigny, 1842, which comes from the Silurian of Bolivia; Schuchert, Reference Schuchert1897, p. 287; Bassler, Reference Bassler1915, p. 892) is dated 1844 by Gray (Reference Gray1853, p. 85), whereas Bittner (Reference Bittner1889, p. 159) and Sherborne (Reference Sherborne1927, p. 3053) give the date 1845. As often in the nineteenth century, the monograph by Klipstein was apparently printed during several years; the date given by the Index Animalium (Sherborne, Reference Sherborne1927) is accepted here.

Cassianospira humboldtii is known from the Carnian of the Alps. It differs from Cassianospira loczyi (Bittner, Reference Bittner1900) in having the median plica on the dorsal valve of the same height as the admedian pair of plicae (lower than the lateral ones in C. loczyi). Cassianospira klipsteinii (Bittner, Reference Bittner1889) is another similar species differing in higher interarea (Bittner Reference Bittner1890, pl. 2, figs 30–31; Zardini, Reference Zardini1988, pl. 10, fig. 13)

Order Spiriferidina Ivanova, Reference Ivanova1972

Suborder Cyrtinidina Carter and Johnson in Carter et al., Reference Carter, Johnson, Gourvennec and Hou1994

Superfamily Suessioidea Waagen, Reference Waagen1883

Family Bittnerulidae Schuchert in Schuchert and LeVene, Reference Schuchert and LeVene1929

Subfamily Bittnerulinae Schuchert in Schuchert and LeVene, Reference Schuchert and LeVene1929

Genus Thecocyrtella Bittner, Reference Bittner1892

Type species

Cyrtotheca ampezzana Bittner, Reference Bittner1890; Cortina d’Ampezzo, Alps; Carnian.

Remarks

Carter (Reference Carter2006, p. 1889) included absence of fold and sulcus among diagnostic characters of Thecocyrtella. T. dagysii is similar to T. ampezzana in internal characters but possesses a ventral sulcus; we consider that this is not a character justifying separation at genus level but rather a reason for the emendation of the diagnosis; the discussed fragment should run “sulcus absent or present”.

Thecocyrtella dagysii new species

Figures 4.1, 4–34; 5

Figure 4

(1, 4–34) Thecocyrtella dagysii Halamski, Bitner, Kaim, Kolar-Jurkovšek, and Jurkovšek n. sp. (1) A poorly preserved shell BJ 3081 attached to a fragment of a thallus of a (dasyclad?) alga. (4) Punctae (seen from inside) of the shell ZPAL Bp 72/3/1. (5, 10) Dorsal interior BJ 3084, general view and enlargement of the cardinalia. (6, 7) Dorsal interior BJ 3085 in oblique and ventral views. (8, 9) Juvenile articulated shell BJ 3098, dorsal view and enlargement of the interarea. (11) Dorsal interior BJ 3104 showing crura. (12, 13) Ventral valve BJ 3087, dorsal view and enlargement of the deltidium. (14–18) Four ventral valves ZPAL Bp 72/3/1, BJ 3095, 3094, and 3093 in dorsal views and an enlargement of the interarea. (19, 24) Articulated shell BJ 3086 in postero-dorsal view and enlargement of the interarea. (20–23) Four ventral valves 3089, 3092, 3102, and 3103 in ventral views. (25–29) Five articulated shells BJ 3096, 3101, 3099, 3100, and 3097 in postero-dorsal views. (30–34) Holotype BJ 3083 in dorsal, ventral, lateral, anterior, and posterior views. (2) Albasphe albertimagni Halamski, Bitner, Kaim, Kolar-Jurkovšek, and Jurkovšek n. gen. n. sp.; punctae (seen from inside) of the shell ZPAL Bp 72/2/6. (3) Flabellocyrtia flabellulum Chorowicz and Termier, Reference Chorowicz and Termier1975; punctae (seen from inside) of the shell BJ 3082. (1–29) SEM micrographs; (30–34) images taken in visible light.

Figure 5

Thecocyrtella dagysii Halamski, Bitner, Kaim, Kolar-Jurkovšek, and Jurkovšek n. sp.: X-ray microtomograph sections of the holotype BJ 3083. (1) Sections parallel to the delthyrium, distances (in mm) measured from front; (2) sections parallel to the commissural plane, distances (in mm) measured from the tip of the ventral umbo; (3) sections parallel to the symmetry plane, distances (in mm) measured either side from the latter. J=jugum, s=septum, sn=spondylium, sp=spiralium.

Type material

Holotype, BJ 3083.0; illustrated paratypes, BJ 3081, 3084–3101; ZPAL Bp 72/3/1; type locality, Svilaja, Dinarides; cherty limestones and dolomites, Ladinian, Middle Triassic.

Diagnosis

Thecocyrtella with a deep ventral sulcus.

Dimensions

Holotype BJ 3083: length 2.7 mm; width 2.1 mm; thickness 2.2 mm.

Description

Shell very strongly ventribiconvex. Dorsal valve medially indented, nearly flat, hinge line straight, postero-lateral extremities auriculate; maximal width at hinge line; a strong median rib present in some specimens (Fig. 4.28–4.30), sometimes situated in the middle of a faint sulcus (Fig. 4.30). Ventral valve pyramidal, beak incurved, with a narrow, deep V-shaped median groove originating at umbo; lateral slopes mostly smooth, seldom with faint plication. Interarea very high, apsacline, concave; delthyrium narrow (0.11–0.16 of the area width), with subparallel edges, covered by a wider (0.28–0.37 of the area width) deltidium (Fig. 4.9, 4.13, 4.19; rarely preserved, cf. supra). Shell substance punctate (Fig. 4.4).

Dorsal interior: crura subparallel (Fig. 4.7) or divergent (Fig. 4.5, 4.10), then coalescing to form a jugum (Figs 4.11; 5.1, section at 0.918 mm; 5.2, section at 1.557 mm); spiralium continuing quite far towards the ventral beak but less than one entire whorl is preserved (Fig. 5.3). Ventral interior: median septum thin, moderately high, not very long; spondylium (Fig. 5.1, sections at 2.150 and 2.296 mm) present in umbonal region (0.4 mm long in a specimen 2.4 mm long); teeth small.

Etymology

In honor of Algirdas Dagys (30.08.1932–7.01.2000), Lithuanian paleontologist, in recognition of his contribution to the study of Triassic brachiopods (name Latinised as Dagysius, then genitive Dagysii).

Material

One hundred and thirty-three articulated shells, 101 ventral valves, and 12 dorsal valves (paratypes).

Remarks

The described material is included in Thecocyrtella Bittner, Reference Bittner1892 on account on shape, minute size, (near) lack of radial ornamentation, and possession of a ventral septum and a spondylium. Dagys (Reference Dagys1974, p. 149) showed that Bittner (Reference Bittner1890) misinterpreted an incomplete beak of the type species T. ampezzana (Bittner, Reference Bittner1890) as representing an attachment scar (a similar condition is shown in Fig. 4.19); as a matter of fact, there is no such structure in the discussed genus. For the terminological question of deltidium vs. symphytium, cf. infra, remarks on Flabellocyrtia flabellulum.

T. dagysii n. sp. differs from T. ampezzana and from T. orientalis Ivanova in Dagys, Reference Dagys1965 [this species was sometimes cited as “T. orientalis Ivanova, Reference Ivanova1960” but the original publication (Ivanova, Reference Ivanova1960, p. 279, text-fig. 407, pl. 64: 9) was without either description or diagnosis; the first to provide a diagnosis was Dagys (Reference Dagys1965, p. 107), so the name must be considered as validly introduced only in the latter publication] in having a deep ventral sulcus. Bittnerula zitteli (Bittner, Reference Bittner1890) (syn. Spirifer buchii von Klipstein, 1843; Dagys, Reference Dagys1974 considered Bittnerula as a synonym of Thecocyrtella) has a weaker ventral sulcus and a much higher interarea. Thecocyrtelloidea tubulosa Yang and Xu, 1966 from the Anisian of Guizhou has no spondylium and its spiralium has at least five whorls (Yang and Xu, 1966).

The interpretation of brachiopods described herein under Thecocyrtella dagysii n. sp. as post-Paleozoic productides was proposed in a preliminary communication by Jaecks et al. (Reference Jaecks, Leighton, Kolar-Jurkovšek, Jurkovšek and Jelaska2003) without knowledge of the internal structures, which are crucial for correct identification. Moreover, Jaecks et al. (Reference Jaecks, Leighton, Kolar-Jurkovšek, Jurkovšek and Jelaska2003) misinterpreted some poorly preserved unidentified epizoans in the umbonal region of some specimens as alleged productide spines.

Subfamily Hirsutellinae Xu and Liu, Reference Xu and Liu1983

Genus Flabellocyrtia Chorowicz and Termier, Reference Chorowicz and Termier1975

Type species

Flabellocyrtia flabellulum Chorowicz and Termier, Reference Chorowicz and Termier1975; Svilaja; Ladinian.

Flabellocyrtia flabellulum Chorowicz and Termier, Reference Chorowicz and Termier1975

Figures 4.3, 6, 7

Figure 6

Flabellocyrtia flabellulum Chorowicz and Termier, Reference Chorowicz and Termier1975: external and internal morphology of shells. (1–3) articulated shells BJ 3105, 3070, and 3072 showing different preservation of the deltidium (preserved in 1, 2; not preserved in 3). (4–7) Articulated shells ZPAL Bp 72/1/3 and 72/1/4 in dorsal and posterior views. (8) Fragmentary dorsal valve ZPAL Bp 72/1/5 with an almost entire crus. (9–18) Articulated shells ZPAL Bp 72/1/1 and 72/1/2 in dorsal, ventral, lateral, anterior, and posterior views. (19–30) Dorsal interiors BJ 3062 (19), 3061 (20, 24, 28), 3060 (21, 25, 29), 3059 (22, 26, 30), and 3058 (23, 27), general views (19–23), enlargements of cardinalia (24–27), and of marginal regions (28–30). (31, 36) Fragments of spiralium BJ 3068 and 3069 showing spines. (32, 37) Fragmentary ventral valves BJ 3063 and 3064 (apical regions preserved) in antero-lateral view showing different shapes of the median septum. (33) Ventral valve BJ 3065 showing spiralium. (34–35) Ventral valves BJ 3066 and 3067 in postero-dorsal views. (1–3, 8, 19–37) SEM micrographs; (4–7, 9–18) images taken in visible light.

Figure 7

Flabellocyrtia flabellulum Chorowicz and Termier, Reference Chorowicz and Termier1975: X-ray microtomograph sections of the articulated shell BJ 3106. (1) Sections parallel to the delthyrium, distances (in mm) measured from the tip of the ventral umbo; (2) sections parallel to the commissural plane, distances as above; (3) sections parallel to the symmetry plane, distances (in mm) measured either side from the latter. S=septum, sp=spiralium, t=tichorhinum.

*1975 Flabellocyrtia flabellulum Chorowicz and Termier, p. 235–237; text-fig. 4; pl. 20, figs 5–13.

Type material

Specimens figured by Chorowicz and Termier (Reference Chorowicz and Termier1975: text-fig. 4, pl. 20, figs 5–13), syntypes; repository unknown [not traced in UPMC, MNHN, FLS, and UCBL].

Description

Shell up to 8.6 mm in width, wider than long, very strongly ventribiconvex. Anterior commissure weakly unisulcate. Dorsal valve weakly convex with a wide, triangular median sulcus to more seldom weakly concave; maximal width at hinge line or about the posterior third; hinge line straight; interarea sublinear. Ventral valve: interarea approximately catacline, high, incurved; delthyrium occupying about one sixth to one fifth of the interarea width, closed by a seldom preserved deltidium (Fig. 6.1, 6.2, 6.5, 6.7; incomplete in the umbonal region in all studied specimens). Ornamentation of strong, acute plicae separated by V-shaped furrows about as wide as the plicae; a median plica and 3(–4) lateral ones per flank on the dorsal valve; ventrally up to five pairs of plicae. Shell substance punctate (Fig. 4.3).

Dorsal interior: External plications reflected on the internal side on the valve. Cardinal process (ctenophoridium) multilobate (Fig. 6.25, 6.26), situated on a wide platform (Fig. 6.24–6.27) extending through the median third of the valve width, giving rise laterally to crura (Fig. 6.8) and narrow, posteriorly directed hinge plates (Fig. 6.25). Crura stout, wide, anteriorly directed (Figs 6.8; 7.2, section at 3.578 mm), diverging at 40°–70°, long, extending nearly to the antero-lateral margin. Radial traces of narrow mantle canals present in marginal region (Fig.6.28–6.30). Spiralium of about four whorls (Fig. 6.33; 7.1, section at 3.377 mm); hollow spines can sometimes be observed on external sides of the first whorl (Fig. 6.31, 6.36; 7.2, section at 3.226 mm, enlargement; 7.3, section at 0.924 mm, enlargement).

Ventral interior: Teeth flat, relatively wide (Fig. 6.34, 6.35). Median septum posteriorly with a tichorhinum (Fig. 7.2, section at 0.465 mm), the canal thereof without a septum; anteriorly septum high, blade-like (Fig. 6.32, 6.37).

Material

Eight hundred seventy-two articulated shells, 192 ventral valves, and 241 dorsal valves; collection numbers BJ 3058–3072, 3082, 3105–3106; ZPAL Bp 72/1.

Dimensions (in mm)

ZPAL Bp 72/1/3: length (l) 6.8, length of the dorsal valve (d) 5.3, width (w) 6.3, thickness (t) 5.7; ZPAL Bp 72/1/4: l 8.5, d 5.7, w 6.5, t 5.4; ZPAL Bp 72/1/1: l 6.0, d 4.8, w 7.3, t 5.4; ZPAL Bp 72/1/4: l 8.4, d 6.4, w 8.0, t 6.9.

Remarks

The dorsal cardinalia were interpreted by Chorowicz and Termier (Reference Chorowicz and Termier1975, p. 236) as consisting of a large cardinal process occupying one third of the valve length linked to short crura. As a matter of fact, the cardinal process (ctenophoridium, similarly as in Hirsutella, the type genus of the subfamily to which Flabellocyrtia belongs) is of usual size but situated on a wide platform and the crura are long (see description above). The structures closing the delthyrium of Flabellocyrtia and Thecocyrtella are called deltidium by Carter (Reference Carter2006); in the material studied no median line of junction could be observed, wherefore, following Williams and Brunton (Reference Williams and Brunton1996), the term ‘symphytium’ would theoretically be more appropriate; the present authors decided to follow the general usage reflecting the fact that such a junction line is seldom preserved in the fossil material (R. Gourvennec, pers. comm., March 2014).

Order Terebratulida Waagen, Reference Waagen1883

Suborder Gwyniidina Halamski and Bitner, new

Diagnosis

Terebratulida with secondarily lost loop; lophophore supported by submarginal ridges in some representatives.

Remarks

Representatives of the order Terebratulida are characterized by the lophophore being supported by a loop (Cloud, Reference Cloud1942; Williams and Wright, Reference Williams and Wright1961; Cooper, Reference Cooper1983; Boucot and Wilson, Reference Boucot and Wilson1994; MacKinnon and Lee, Reference MacKinnon and Lee2006), originating either alone (suborder Terebratulidina) or in conjunction with the septal pillar (suborder Terebratellidina) (MacKinnon and Lee, Reference MacKinnon and Lee2006). The identification of an early-branching (Permian to Recent) lineage of terebratulides lacking a loop, even if such a simplification be not a strictly unique case among over six hundred genera belonging to this order (cf. infra, Gwynioidea, remarks), justifies the erection of a new suborder. Such a proposal is supported by results of molecular studies that place Recent Gwynia in an isolated position, namely as a basal branch of the terebratellidines (Cohen, Reference Cohen2007), although with relatively weak support (personal communication, B. Cohen, 2013).

Superfamily Gwynioidea MacKinnon, Reference MacKinnon2006

Diagnosis

Shell minute, punctate, rounded to medially indented in outline. Loop absent. Submarginal ridges supporting the lophophore present in some representatives. Cardinal process weakly developed or absent. Dental plates absent. Septa with internal cavities, either ventral or dorsal, present in some representatives.

Families included

Dispheniidae Grant, Reference Grant1988; Gwyniidae MacKinnon, Reference MacKinnon2006 (nomen translatum ex Gwynioidea MacKinnon, Reference MacKinnon2006; herein).

Remarks

The superfamily Gwynioidea MacKinnon, Reference MacKinnon2006 was introduced (MacKinnon Reference MacKinnon2006) for two related (Logan et al., Reference Logan, MacKinnon and Phorson1997) genera of minute brachiopods characterized by presence of submarginal ridges supporting the lophophore, Recent Gwynia (Logan et al., Reference Logan, MacKinnon and Phorson1997; Simon and Willems, Reference Simon and Willems1999; Álvarez and Emig, Reference Álvarez and Emig2005) and Jurassic Zellania (Baker, Reference Baker1970). The latter is closely related to Triassic Albasphe n. gen. described herein, which in its turn appears to be an evolutionary descendant of Permian Disphenia. Bitner et al. (Reference Bitner, Melnik and Zezina2013) described the Recent genus Simpliciforma in which the diagnostic submarginal ridges have been lost secondarily. The absence of submarginal ridges in the specimen described by Lüter (Reference Lüter2008) as Gwynia macrodentata allows to transfer this species to the genus Simpliciforma (see also comments in Bitner et al., Reference Bitner, Melnik and Zezina2013, p. 287). The links between each pair of stratigraphically successive genera are clear but the entire evolutionary line defined in this way is much less easy to characterize. The superfamily Gwynioidea is redefined herein to include two families, Paleozoic to Mesozoic Dispheniidae Grant, Reference Grant1988 and Pleistocene to Recent Gwyniidae MacKinnon, Reference MacKinnon2006 (for nomenclatural issue related to such a treatment, see Appendix). Baker (Reference Baker1970) convincingly showed that probable affinities of Zellania were with primitive terebratulides belonging to the superfamily Stringocephaloidea King, Reference King1850; nonetheless, he refrained from formally proposing such a conclusion on account of the stratigraphic gap between Devonian Stringocephaloidea and Middle Jurassic Zellania. Discovery of Permian and Triassic predecessors of the latter genus eliminates this objection and the superfamily Gwynioidea can be interpreted as descending from a representative of the suborder Terebratulidina Waagen, Reference Waagen1883 (incerti subordinis in MacKinnon, Reference MacKinnon2006). The comparison of all five genera belonging to the superfamily Gwynioidea is given in Table 2. A new formal classification of the superfamily Gwynioidea is given in the Appendix.

Table 2

Comparison of Permian to Recent representatives of Gwyniidina new suborder

Grant (Reference Grant1988) suggested (without giving any reason) that Dispheniidae might be related to the superfamily Zeillerioidea Schuchert in Schuchert & LeVene, Reference Schuchert and LeVene1929. Such a classification was probably inspired by shape similarity (indented anterior margin) between Disphenia and well-known Liassic representatives of Zeilleria like Z. cor (Delance, Reference Delance1974). However, zeillerioids are quite different, having a well-developed loop and a mesothyrid or permesothyrid foramen (Baker, Reference Baker2006). Generally speaking, shape alone is a poor taxonomic character in brachiopods. For example, Halamski and Segit (Reference Halamski and Segit2006) disproved an evolutionary scheme among Paleozoic terebratulides based on external shapes on account of micro-ornamentation. Such a criterion is unfortunately not utilisable in the lineage studied: Disphenia and Albasphe are known solely from silicified specimens, so the information is missing; Zellania, Gwynia, and Simpliciforma are entirely devoid of micro-ornamentation. Weakly developed cardinal process in Disphenia myiodes may also have been an argument for a relationship with the Zeillerioidea in which a cardinal process is most often absent (Baker, Reference Baker2006). However, among the Terebratulida cardinal process presence or absence does not seem to be such an important taxonomic criterion as, for example, in Rhynchonellida. Among nine species of the genus Xenobrochus (Dyscolioidea, Terebratulidina) most possess a cardinal process but three species have lost it secondarily (Bitner, Reference Bitner2011). Grant’s (Reference Grant1988) suggestion is therefore rejected herein and the family Dispheniidae is accommodated within the Gwynioidea (see diagnosis above).

In a preliminary communication Savage (Reference Savage2005) suggested that Disphenia and Cardiarina Cooper, Reference Cooper1956 (the latter originally described as a possible rhynchonellide) may be related and both included into the Terebratulida; however, in the definitive treatment of the same matter (Savage, Reference Savage2006) Cardiarina has been considered as incertae sedis and Disphenia was omitted. Cardiarina seems unrelated to Disphenia given lack of septa in both valves and different microstructure (impunctate in the former, punctate in the latter); it has been interpreted as a possible representative of the Lambdarinidae by Baliński and Sun (Reference Baliński and Sun2008).

The Recent species Simplicithyris kurilensis Zezina, Reference Zezina1976, lacking both crura and loop, has strong dental plates (Zezina, Reference Zezina1976); this character distinguishes it from all representatives of the Gwynioidea (cf. supra, diagnosis). The systematic position of another Recent terebratulide species lacking a loop, Oceanothyris juveniformis Bitner and Zezina in Bitner et al., Reference Bitner, Melnik and Zezina2013, requires further investigation. Despite the similarity of name reflecting external homeomorphy, the Paleocene genus Gwyniella Johansen, Reference Johansen1987 is unrelated to Gwynia; it possesses a poorly developed brachidium and was tentatively assigned to the family Megathyrididae by Johansen (Reference Johansen1987, p. 26; superfamily and family uncertain in Lee et al., Reference Lee, MacKinnon and Smirnova2007).

Family Dispheniidae Grant, Reference Grant1988

Diagnosis

Gwynioidea possessing either a dorsal or a ventral septum with an intra-septal cavity.

Subfamily Albasphinae Halamski and Bitner, new

Diagnosis

Dispheniidae with submarginal ridges and the dorsal septum with a cavity.

Genera included

Albasphe n. gen., Ladinian (Middle Triassic); Zellania Moore, Reference Moore1855, Early to Middle Jurassic (discussion on stratigraphic range of this genus is reported to the Appendix).

Genus Albasphe new genus

Type species

Albasphe albertimagni n. gen. n. sp., as below.

Other species

Type species only.

Diagnosis

Shell minute, rounded to bilobate in outline. Ventral valve: accessory ridges absent; median septum absent, sometimes a low myophragm present. Dorsal valve: delthyrium open; median septum high, with an intra-septal cavity; submarginal ridges present.

Etymology

An arbitrary combination of letters consisting of alb, for Albertus and of a, without and sphe from Greek sphen, wedge; the first part from the specific epithet, the second and the third to recall that the new genus has not the wedge-shaped outline unlike its probable evolutionary predecessor Disphenia. The genus name is feminine.

Remarks

Albasphe n. gen. differs from the Jurassic Zellania in the anatomy of the ventral valve, namely in lack of accessory ridges (present in the latter) and weak development of the septum (only a short and low ridge vs. a high and long blade-like ventral septum in Zellania), as well as in larger size.

Albasphe albertimagni new species

Figures 4.2, 8, 9, 10

Figure 8

Albasphe albertimagni Halamski, Bitner, Kaim, Kolar-Jurkovšek, and Jurkovšek n. gen. n. sp. (1–2, 8–9, 13, 14) Ventral valves ZPAL Bp 72/2/6, 72/2/5, BJ 3079, and 3080 in oblique (1, 8) and dorsal (2, 9, 13, 14) views. (3–7, 10, 11–12, 15–16, 20–21) Dorsal valves ZPAL Bp 72/2/7, BJ 3078, 3076, 3077, 3075, ZPAL Bp 72/2/4, and 72/2/1 in ventral (3, 4, 6, 10, 11, 15, 20) and oblique (5, 7, 12, 16, 21) views. (17–19) Articulated shells ZPAL Bp 72/2/2 and 72/2/3 in dorsal views (17, 19) and enlargement of the delthyrium (18). (22–31) Articulated shells BP 3074 and 3073 (holotype) in dorsal, ventral, lateral, posterior, and anterior views. (1–21) SEM micrographs. (22–31) images taken in visible light.

Figure 9

Albasphe albertimagni Halamski, Bitner, Kaim, Kolar-Jurkovšek, and Jurkovšek n. gen. n. sp. (1) Transverse section through the shell (based on the section at 1.422 mm in Fig. 10.1). (2) Reconstructions of internal structures showing both valves in oblique views (not to scale).

Figure 10

Albasphe albertimagni Halamski, Bitner, Kaim, Kolar-Jurkovšek, and Jurkovšek n. gen. n. sp.: X-ray microtomograph sections of the holotype BJ 3073. (1) Transversal sections, distances (in mm) measured from the tip of the ventral umbo; (2) sections parallel to the commissural plane, distances (in mm) measured from the highest point of the dorsal valve; (3) Sections parallel to the symmetry plane, distances (in mm) measured either side from the latter.

Type material

Holotype, BJ 3073; illustrated paratypes, BJ 3073–3080, ZPAL Bp 72/2/1–7; type locality, Svilaja, Dinarides; cherty limestones and dolomites, Ladinian, Middle Triassic.

Diagnosis

As for the genus.

Description

Shell teardrop-shaped and rounded (Fig. 8.17, 8.22) to transversely subtriangular in outline (Fig. 8.19, 8.27), width to length ratio 0.90–1.33 (mean 1.08; N=20); in the latter case bilobed through a median indentation of the anterior commissure, the length of the indentation not exceeding one sixth of that of the dorsal valve; weakly to moderately ventribiconvex. Maximal width of the shell at about ⅔ of its length. Anterior commissure gently unisulcate. Dorsal valve moderately convex, in transverse individuals with a V-shaped sulcus; beak acute. Ventral valve convex either with a weak sublinear median sulcus (Fig. 8.28, 8.31) or regularly convex (Fig. 8.23, 8.26); beak nearly straight; delthyrium open (Fig. 8.18), symphytium absent. Shell smooth; shell substance punctate (Fig. 4.2); micro-ornamentation, if any, not preserved.

Dorsal interior: median septum beginning about the posterior fourth of the valve length, rising abruptly and arching backwards, its posterior extremity thus consisting in lateral profile of a rounded sinus in the lower part and of an overhanging upper part (Fig. 8.7, 8.12, 8.16), nearly reaching the ventral valve floor (Fig. 9.1), then bifurcating about the midlength of the valve, thus forming an internal cavity, open anteriorly in form of an isosceles concave-sided triangle (Fig. 8.6, 8.11, 8.15). Submarginal ridges situated in the immediate proximity of the margin, the angular length of each ridge ca. 90° (Fig. 8.10). Inner socket ridges either of the same thickness as the submarginal ridges of which they form a mere continuation (Figs 8.12, 9.2) or much thicker (Fig. 8.3).

Ventral interior: a short and low myophragm is present in some specimens (Fig. 8.1, 8.13); faint muscle scars on its either scars are visible in a single shell (Fig. 8.13); accessory ridges absent; teeth rounded, stout but rather small (Fig. 8.14).

Etymology

In honor of Albertus Magnus (ca. 1200–15.11.1280), naturalist.

Material

One hundred and sixty-one articulated shells, 17 ventral valves, and 25 dorsal valves.

Dimensions

Holotype BJ 3073: length 2.1 mm; width 2.6 mm; thickness 1.0 mm. Paratype BJ 3074: length 2.3 mm; width 2.1 mm; thickness 1.2 mm.

Remarks

Albasphe albertimagni n. gen. n. sp. shows important shape variability. In a single sample both rounded and bilobate individuals are found, the former resembling the inferred evolutionary predecessor Disphenia, the latter similar to the inferred descendant Zellania. This variability cannot be explained by ontogenetic differences alone, as rounded individuals (“morphological juveniles”) attain a size comparable to that of bilobed individuals (compare Fig. 8.22 and 8.27 representing shells 2.3 and 2.1 mm long, respectively).

A. albertimagni is externally homoeomorphic with representatives of the family Lambdarinidae (Rhynchonellida, Late Devonian to Permian) from which it is distinguished by shell microstructure and internal features. In the Lambdarinidae such a shape difference as seen in the studied sample is indicative of a distinction at genus level (bilobed: Lambdarina; rounded: Dacryrina; Baliński and Sun, Reference Baliński and Sun2008).

Suborder Terebratulidina Waagen, Reference Waagen1883

Superfamily and family unknown

Terebratulidina? gen. et sp. indet.

Figure 3.17–3.21

Material

A single fragmentary adult specimen and two complete articulated shells of juvenile specimens.

Remarks

The material is very limited and poorly preserved, precluding any precise determination. Nevertheless, a smooth, biconvex shell with astrophic hinge line, a large, labiate permesothyrid foramen, and a partly visible symphytium strongly suggest the suborder Terebratulidina; similar morphologies, however, do occur among representatives of the order Athyridida, so in absence of diagnostic interior characters such an assignment cannot be excluded either (even if judged much less probable by the authors).