1. Geological setting

The Quebrada Oblicua constitutes a typical Cambrian fossil locality in the San Isidro area. It is located on the south side of the Quebrada La Cruz, which runs along the southern flank of Cerro Áspero, about 15 km W of Mendoza city (see location map in Tortello Reference Tortello2020, fig. 1; geographic coordinates [32º51′13′′S, 69º00′18′′W]). There, decimetre- to metre-sized allochthonous carbonate blocks with different Miaolingian and Furongian open marine faunas (San Isidro and La Cruz olistoliths; Bordonaro et al. Reference Bordonaro, Beresi and Keller1993; Bordonaro & Banchig Reference Bordonaro and Banchig1996; Bordonaro Reference Bordonaro2003) are emplaced in Middle and Upper Ordovician green shales of the San Isidro/Empozada Formation (Heredia & Beresi Reference Heredia and Beresi2004).

The material revised in this paper comes from two dark grey blocks from La Cruz olistoliths (La Cruz Limestone sensu Keller Reference Keller1999) that were labelled by Rusconi (Reference Rusconi1958) as ‘2: Block with Tabalqueia’ and ‘3: Block with Cedaria’.

2. Biostratigraphy

Block 2 (=block with Tabalqueia) contains a moderately diverse assemblage composed, as revised herein, of Pseudagnostus cf. P. idalis Öpik, Reference Öpik1967, Dunderbergia punctata (Rusconi, Reference Rusconi1958), Sigmocheilus cf. S. sigmoidalis (Palmer, Reference Palmer1954), Litocephalus obliquoanus (Rusconi, Reference Rusconi1958) and Onchonotopsidae? gen. et sp. indet., whereas Block 3 (=block with Cedaria) is dominated by Cedaria puelchana Rusconi, Reference Rusconi1954a.

Taxa from Block 2 have variable biostratigraphic implications. As stated by Shergold (Reference Shergold1977) and Pratt (Reference Pratt1992), Pseudagnostus Jaekel, Reference Jaekel1909 is a cosmopolitan, long-ranging and ecologically tolerant genus that is commonly found in places that had a connection to open sea environments. Although its stratigraphic range encompasses the Furongian–Lower Ordovician, the material from Quebrada Oblicua shows a particular affinity with Steptoean (Paibian–lower Jiangshanian) species (see Section 3. Systematic palaeontology).

In addition, Dunderbergia Walcott, Reference Walcott1924, Sigmocheilus Palmer, Reference Palmer1960, and Litocephalus Resser, Reference Resser1937, which are recorded in Argentina for the first time, provide more accurate biostratigraphic and palaeobiogeographic information since they are typical lower Furongian genera from North America (e.g., Lochman-Balk & Wilson Reference Lochman-Balk and Wilson1958, text-fig. 12; Palmer Reference Palmer1960, Reference Palmer1965; Pratt Reference Pratt1992). As stated below, the species D. punctata, S. cf. S. sigmoidalis and L. obliquoanus compare most closely with material from the Dunderbergia Zone (upper Paibian) of the standard North American trilobite zonation (Palmer Reference Palmer1960, Reference Palmer1965; Rasetti Reference Rasetti1961). The sole previous report of this zone in the Argentinian Precordillera was provided cautiously by Shergold et al. (Reference Shergold, Bordonaro and Liñán1995), based only on the record of agnostoids (Pseudagnostus [P.] idalis Öpik, Reference Öpik1967, Oncagnostus [Oncagnostus] sp., and Acmarhachis cf. A. acuta [Kobayashi, Reference Kobayashi1938]) from allochthonous blocks in the Empozada and Los Sombreros formations.

For its part, Block 3 is regarded as late Guzhangian (latest Miaolingian) in age on the basis of the occurrence of Cedaria puelchana. This species was previously described from the Cedaria prolifica Zone of 200 m NW of Estancia San Isidro (San Isidro area, Mendoza), in association with Kormagnostus seclusus (Walcott, Reference Walcott1884), C. prolifica Walcott, Reference Walcott1924, Tricrepicephalus texanus (Shumard, Reference Shumard1861) and Meteoraspis metra (Walcott, Reference Walcott1890), among others (Rusconi Reference Rusconi1954a; Tortello Reference Tortello2023), which enable correlation with the lower Crepicephalus Zone of the traditional North American genus-based zonation.

3. Systematic palaeontology

The specimens examined are housed in the Museo de Ciencias Naturales y Antropológicas ‘Juan Cornelio Moyano’ (Mendoza City, Argentina) with the prefix MCNAM. Before photography, the material was coated with magnesium oxide smoke from burning magnesium ribbon.

Abbreviations: sag, sagittally; exs, exsagittally; long, longitudinally; tr, transversally.

Type species. Agnostus cyclopyge Tullberg, Reference Tullberg1880, from the Furongian of Sweden, by original designation.

Figure 1

(a–b) Pseudagnostus cf. P. idalis Öpik, Reference Öpik1967: (a) exfoliated cephalon, MCNAM 21047a; (b) testate pygidium, MCNAM 21013a. (c–w) Dunderbergia punctata (Rusconi, Reference Rusconi1958): (c, e–g) cranidium in lateral (c), dorsal (e), anterior (f) and posterior (g) views, MCNAM 20995, holotype (illustrated previously with a sketch, Rusconi Reference Rusconi1958, fig. 2a–b); (d) cranidium, latex cast of holotype showing complete anterior border and indications of ocular ridges, MCNAM 20995; (h–i, l–m) cranidium in dorsal (h), anterior (i), posterior (l) and lateral (m) views, MCNAM 20996, paratype (not illustrated previously); (j–k, n) cranidium in dorsal (j), anterior (k) and lateral (n) views, MCNAM 20997, paratype (not illustrated previously); (o, r) cranidium in lateral (o) and dorsal (r) views, MCNAM 21006; (p, t) librigena in dorsal (p) and lateral (t) views, MCNAM 21011 (illustrated previously with a sketch, Rusconi Reference Rusconi1958, fig. 2a); (q, u) cranidium in dorsal (q) and anterior (u) views, MCNAM 21003; (s) librigena, MCNAM 21014 (see also Fig. 2e–f); (v–w) librigena in dorsal (v) and oblique (w) views, MCNAM 21010. All from Block 2, lower Furongian (Paibian) of Quebrada Oblicua, San Isidro area, Mendoza. (a–b) Scale bars = 1 mm; (c–w) scale bars = 4 mm.

Occurrence. Two cephala and one pygidium (MCNAM 21013a, 21047a, b), Quebrada Oblicua, Mendoza, La Cruz Olistoliths, Dunderbergia Zone, upper Paibian.

Remarks. Three agnostoid sclerites (two cephala and one pygidium) from Block 2 show a subcircular outline; broad, well-incised (deliquate) border furrows; a complete preglabellar median furrow; a long (sag.), wide (tr.), hemicylindrical glabella with a proportionally large anteroglabella, a backwardly bowed F3 furrow, and an anteriorly placed axial node; a subparallel-sided pygidial anteroaxis showing a conspicuous axial node on M2 lobe; an expanded posteroaxis that is weakly defined by imprecise axial furrows; a constricted pygidial acrolobe; and minute posterolateral spines. The presence of a spectaculate condition and an expanded posteroaxis is typical of Pseudagnostus Jaekel, Reference Jaekel1909 (e.g., Öpik Reference Öpik1963; Shergold Reference Shergold1977; Pratt Reference Pratt1992; Westrop Reference Westrop1995; Peng & Robison Reference Peng and Robison2000; Westrop & Eoff Reference Westrop and Eoff2012).

These sclerites are scarce, which precludes full comparisons. Nevertheless, it should be noted that they are similar to Steptoean material known as Pseudagnostus idalis and closely allied forms (e.g., Pseudagnostus [Pseudagnostus] idalis idalis Öpik, Reference Öpik1967 [Australia; Öpik Reference Öpik1967; Shergold Reference Shergold1982, pl. 2, figs 1–13]; P. [P.] idalis huskissonensis Jago & Brown, Reference Jago and Brown1992 [Tasmania; Jago & Brown Reference Jago and Brown1992, pls 1u–w, 2a–o]; ‘P. communis’ [Hall & Whitfield Reference Hall and Whitfield1877] [NW Canada; Pratt Reference Pratt1992, pl. 5, figs 10–34]; P. [P.] idalis idalis and P. [P.] idalis sensu lato [western Argentina; Shergold et al. Reference Shergold, Bordonaro and Liñán1995, pl. 3, figs 1–12]; ‘P. josepha’ [Hall, Reference Hall1863] [Hunan, China; Peng & Robison Reference Peng and Robison2000, fig. 10]; P. cf. P. idalis [eastern Canada; Westrop & Eoff Reference Westrop and Eoff2012, figs 3–4]). Specimens from the Quebrada Oblicua combine a proportionally large anteroglabella, an anteriorly located glabellar median node and a weakly defined pygidial M3; features that are also present in some specimens of ‘P. communis’ from the Rabbitkettle Formation of NW Canada, in which a papilionate condition (Shergold Reference Shergold1977) is approached (see Pratt Reference Pratt1992, p. 34, pl. 5, figs 18, 25).

Pseudagnostus (P.) idalis previously described from allochthonous blocks of the Argentinian Precordillera includes specimens which also have a relatively wide (tr.) glabella and a large anterior glabellar lobe (see Shergold et al. Reference Shergold, Bordonaro and Liñán1995, pl. 3, fig. 7); however, they differ slightly from the present material by their subcentrally positioned axial glabellar node and their better delineated posteroaxis.

Type species. Crepicephalus (Loganellus) nitidus Hall & Whitfield, Reference Hall and Whitfield1877, from the lower Furongian of Nevada, by original designation.

Figure 2

(a–b, e–f) Dunderbergia punctata (Rusconi, Reference Rusconi1958): (a) fragmentary cranidium, MCNAM 21100; (b) librigena in oblique view (see also Fig. 1p, t), MCNAM 21011; (e–f) librigena in posterior (e) and lateral (f) views (see also Fig. 1s), MCNAM 21014; (c–d, g–n) Sigmocheilus cf. S. sigmoidalis (Palmer, Reference Palmer1954): (c–d, h) pygidium in dorsal (c), posterior-dorsal (d) and lateral (h) views, MCNAM 21012; (g) cranidium, MCNAM 21037; (i, n) pygidium in dorsal (i) and lateral (n) views, MCNAM 21020; (j) pygidium, MCNAM 21017; (k) pygidium, MCNAM 21021, latex cast of specimen figured in (j); (l) fragmentary pygidium, MCNAM 21018; (m) fragmentary pygidium, MCNAM 21022. (o–s) Litocephalus obliquoanus (Rusconi, Reference Rusconi1958): (o–p, s) pygidium in lateral (o), dorsal (p) and posterior (s) views, MCNAM 21025, holotype (illustrated previously with a sketch, Rusconi Reference Rusconi1958, fig. 3a); (q–r) pygidium in lateral (q) and dorsal (r) views, MCNAM 21026, paratype (not illustrated previously; erroneously cited as MCNAM 21126 by Rusconi Reference Rusconi1958, p. 87; see Cerdeño Reference Cerdeño2005). All from Block 2, lower Furongian (Paibian) of Quebrada Oblicua, San Isidro area, Mendoza. Scale bars = 4 mm.

Occurrence. Seven cranidia and four librigenae (MCNAM 20995–20997, 21001, 21003, 21006, 21010, 21011, 21013b, 21014, 21100), Quebrada Oblicua, Mendoza, La Cruz Olistoliths, Dunderbergia Zone, upper Paibian.

Remarks. Rusconi (Reference Rusconi1958, p. 85) erected the genus Tabalqueia Rusconi, Reference Rusconi1958 (type species, T. punctata Rusconi, Reference Rusconi1958) based on granulate cranidia and librigenae (Figs 1c–w, 2a–b, e–f) that exhibit a prominent, subparallel-sided, anteriorly sub-rounded to truncate glabella; weak lateral glabellar furrows; a pointed anterior cranidial margin; slightly divergent anterior branches of the facial suture; faint, backwardly oblique ocular ridges; moderately sized palpebral lobes; proportionately narrow (tr.) palpebral areas of fixigenae; well-defined lateral and posterior cephalic border furrows; and small-sized genal spines. Since this combination of features indicates affinity with Dunderbergia Walcott, Reference Walcott1924 (Palmer Reference Palmer1954, Reference Palmer1960, Reference Palmer1965), Tabalqueia is here suppressed as its junior synonym.

The material studied exhibits a certain range of variability involving distribution of pustules on the cranidium. Coarse scattered granules are generally well developed on the fixigenae, whereas they may be less abundant or be even replaced by very fine closely spaced granules on the glabella. Dunderbergia punctata compares closely with D. variagranula Palmer, Reference Palmer1954, a species reported from the lower Furongian of Texas, Nevada, California and Quebec (Palmer Reference Palmer1954, Reference Palmer1960, Reference Palmer1965; Rasetti Reference Rasetti1961), in sharing distinct scattered granules on the exoskeleton. However, the former is distinguished by having shorter (exsag.) and more posteriorly located palpebral lobes, and genal spines that diverge more strongly from the general curvature of the lateral cephalic margin.

Dunderbergia sp., from boulders in the Cow Head Group of western Newfoundland (Kindle Reference Kindle1982, pl. 1.3, fig. 15), differs from D. punctata by having more anteriorly located palpebral lobes. In addition, Dunderbergia brevispina Palmer, Reference Palmer1965, from the Dicanthopyge Zone of Nevada (Palmer Reference Palmer1965, pl. 5, figs 11–13, 15), is distinguished from D. punctata by its minute genal spines, whereas D. seducta Palmer, Reference Palmer1968, from the lower Furongian of Alaska (Palmer Reference Palmer1968, pl. 7, figs 21, 26–28), exhibits wider (tr.) fixed cheeks opposite the eyes. The type species, D. nitida (Hall & Whitfield, Reference Hall and Whitfield1877), from the Dunderberg Formation of the Great Basin (e.g., Palmer Reference Palmer1960, pl. 4, figs 14–21, 23–24; 1965, pl. 4, figs 1–2, 5–6) and the Rabbitkettle Formation of NW Canada (Pratt Reference Pratt1992, pl. 11, figs 31–32), is easily separated from D. punctata by lacking coarse granules on the test.

Two coarsely granulate species of Dunderbergia, D. convexa Kobayashi, Reference Kobayashi1938 and D. quadrata Kobayashi, Reference Kobayashi1938, described on the basis of only two poorly preserved cranidia from British Columbia, are remarkably similar to D. punctata. Dunderbergia convexa is only slightly differentiated by its more convex and less tapered glabella, and its slightly narrower (tr.) palpebral areas of the fixigenae (Kobayashi Reference Kobayashi1938, p. 182, pl. 15, fig. 32a–b [erroneously cited as D. quadrata in the explanation of pl. 15]; Palmer Reference Palmer1960, pl. 4, fig. 27); whereas D. quadrata has a surface sculpture which, although obscured by the poor state of preservation, seems to be more delicate (Kobayashi Reference Kobayashi1938, pl. 15, fig. 33). Unfortunately, the imperfect nature of the materials precludes more confident discussions on the affinities of these species (cf. Palmer Reference Palmer1960, p. 68).

No pygidia of Dunderbergia type were identified in the collection studied. On the other hand, a group of subrectangular pygidia that was originally assigned with caution to Tabalqueia punctata by Rusconi (Reference Rusconi1958, p. 86, fig. 2c), is reinterpreted herein as Sigmocheilus cf. S. sigmoidalis (Palmer, Reference Palmer1954) (see below).

Type species. Dikellocephalus flabellifer Hall & Whitfield, Reference Hall and Whitfield1877, from the lower Furongian of Nevada (by synonymy with Sigmocheilus serratus Palmer, Reference Palmer1960; see Palmer Reference Palmer1965, p. 73).

Occurrence. One cranidium and six pygidia (MCNAM 21012, 21017, 21018, 21020–21022, 21037), Quebrada Oblicua, Mendoza, La Cruz Olistoliths, Dunderbergia Zone, upper Paibian.

Description. Cranidium slightly convex, with an evenly rounded anterior margin; glabella tapered forward, rounded anteriorly, slightly elevated above fixigenae, outlined by narrow axial furrows, occupying about 65 % of total cranidial length; S1 and S2 moderately developed, oblique and curved backward, disconnected at middle; S3 faint, barely perceptible; occipital ring short (sag.), approximately one-fifth length of glabella, bowed slightly forward laterally; anterior border conspicuous, concave, strongly elevated adjacent to marginal furrow, delimited by a deep narrow (sag.; exsag.) evenly curved border furrow showing small pits; preglabellar field slightly convex, somewhat longer (sag.) than anterior border; anterior branches of facial suture divergent; ocular ridge faint, oblique; palpebral lobe crescentic, too poorly preserved for description; posterior border short (exsag.), convex, bounded by a faint border furrow. A few scattered low granules are barely visible on the anterior border, preglabellar field and fixigena.

Pygidium convex, subrectangular in outline with gently rounded flanks, length about one-half width, with articulating facets at anterior corners and a weak median indentation at posterior margin; axis tapered backward, elevated above level of pleural fields, surrounded by narrow axial furrows, occupying about 28 % of maximum pygidial width and two-thirds of total pygidial length (excluding articulating half-ring), with four or five rings and terminal segment prolonged in a postaxial ridge which does not reach posterior margin; articulating half-ring crescentic; anterior border furrow deep, delimiting a narrow (exsag.) anterior border; pleural fields convex, showing two or three oblique, moderately impressed pleural furrows that disappear on border; doublure broad, extending more than halfway across pleurae and reaching back of axis medially, with sculpture of numerous (about 18) terrace lines; border slightly concave, weakly defined by change in slope at base of pleural fields; line connecting points of greatest pygidial width passes just anterior to end of axis; posterior margin nearly straight or slightly indented, lacking spines. Pleural fields show a small number of dispersed, minute granules.

Remarks. These pygidia were tentatively referred to as Tabalqueia punctata (=Dunderbergia punctata, see above) by Rusconi (Reference Rusconi1958); however, their subrectangular outline, tapered axis, broad doublure, and concave border indicate affinities with Sigmocheilus Palmer, Reference Palmer1960 (Palmer Reference Palmer1960, Reference Palmer1965). An associated incomplete cranidium in the collection (Fig. 2g), regarded here as conspecific, exhibits a concave anterior border, noticeable glabellar furrows, and glabellar and frontal area proportions which are shared with Sigmocheilus sigmoidalis (Palmer, Reference Palmer1954), a species originally described from the Dunderbergia Zone (=‘post-Aphelaspis Zone’) of Central Texas based only on cranidia (Palmer Reference Palmer1954, pl. 86, fig. 5; Palmer Reference Palmer1960, p. 80). However, since the cranidium from Mendoza is poorly preserved, this material is left in open nomenclature.

Sigmocheilus cf. S. sigmoidalis differs from both S. utahensis (Resser, Reference Resser1942) (Resser Reference Resser1942, pl. 15, figs 7–11; Palmer Reference Palmer1960, pl. 9, figs 24–25, 28) and S. grata (Resser, Reference Resser1942) (Resser Reference Resser1942, pl. 15, figs 3–6; Palmer Reference Palmer1960, pl. 9, figs 22–23, 26–27; 1965, pl. 15, figs 16–18), from the lower Furongian of the Great Basin, mainly by its proportionately longer (sag.) preglabellar field. Sigmocheilus notha (Resser, Reference Resser1942), from the upper Dunderberg Formation of Nevada (Resser Reference Resser1942, pl. 14, figs 34–38, pl. 16, figs 39–41; Palmer Reference Palmer1965, pl. 15, figs 7–8, 10–15), is also distinguished by having a less posterolaterally flared pygidial border, whereas S. cf. S. grata (Resser, Reference Resser1942), from the lower Furongian of Alaska (Palmer Reference Palmer1968, pl. 8, figs 20, 25), exhibits a subrectangular glabella.

The absence of both marginal spines and pleural ribs continuing onto pygidial border distinguishes Sigmocheilus cf. S. sigmoidalis from S. pogonipensis (Resser, Reference Resser1942) (Resser Reference Resser1942, pl. 15, figs 1–2; Palmer Reference Palmer1960, pl. 10, figs 4–7; 1965, pl. 15, figs 2, 4, 9) and the type species, S. flabellifer (Hall & Whitfield, Reference Hall and Whitfield1877) (Palmer Reference Palmer1960, pl. 10, figs 1–3; Pratt Reference Pratt1992, pl. 15, fig. 28).

The pygidium of Sigmocheilus cf. S. sigmoidalis resembles that of Labiostria westropi Chatterton & Ludvigsen, Reference Chatterton and Ludvigsen1998, from the Elvinia Zone of British Columbia (Chatterton & Ludvigsen Reference Chatterton and Ludvigsen1998, figs 17–20; Chatterton & Gibb Reference Chatterton and Gibb2016, pl. 23, figs 1–9, pl. 83, fig. 4, pl. 84, fig. 2), mainly in sharing a similar axis and pleural furrows. However, the latter can be differentiated by showing a more uniformly rounded posterior margin, and lacking granules on the pleural fields. In addition, L. westropi further differs from S. cf. S. sigmoidalis by having a cranidium with a convex anterior border, well-developed caeca on the preglabellar field, and narrower (tr.) palpebral areas of the fixigenae.

Type species. Dicellocephalus bilobatus Hall & Whitfield, Reference Hall and Whitfield1877, from the lower Furongian of Nevada (by synonymy with Dicellocephalus richmondensis Walcott, Reference Walcott1884; see Palmer Reference Palmer1956).

1958 Cayupania obliquoana Rusconi, p. 87, fig. 3a (only; fig. 3b–d, Onchonotopsidae? gen. et sp. indet.).

Occurrence. Two pygidia (MCNAM 21025, 21026), Quebrada Oblicua, Mendoza, La Cruz Olistoliths, Dunderbergia Zone, upper Paibian.

Remarks. Rusconi (Reference Rusconi1958) erected Cayupania Rusconi, Reference Rusconi1958 (type species, C. obliquoana Rusconi, Reference Rusconi1958) based on two large semicircular pygidia (Fig. 2o–s) characterised by having a narrow, slightly tapering axis composed of six axial rings and terminal segment; four or five pairs of faint pleural furrows; a poorly defined, concave border; and a wide, deep indentation on the posterior margin. However, the combination of a concave border and a conspicuous notch on the posterior margin is typical of Litocephalus Resser, Reference Resser1937, a genus described from the lower Furongian of the Great Basin and NW Canada (Palmer Reference Palmer1956, Reference Palmer1960, Reference Palmer1965; Pratt Reference Pratt1992). Cayupania Rusconi, Reference Rusconi1958 is therefore considered as a junior synonym of Litocephalus.

It should be noted that the type species, Litocephalus bilobatus (Hall & Whitfield, Reference Hall and Whitfield1877), is imperfectly known. Pratt (Reference Pratt1992) demonstrated that several specimens assigned by Palmer (Reference Palmer1956) to the species were misidentified. The holotype pygidium of L. bilobatus, from the Dunderberg Shale of Eureka District (USGS locality 65), Nevada (Palmer Reference Palmer1956, pl. 73, fig. 2), is similar to L. obliquoanus, although the latter exhibits six rather than four or five axial segments, and fainter pleural furrows.

Litocephalus verruculapeza Palmer, Reference Palmer1960, from the Dunderbergia Zone of Nevada (Palmer Reference Palmer1960, pl. 8, figs 19–20; 1965, pl. 11, fig. 9), differs from L. obliquoanus by having a shorter axis and pairs of coarse granules on the axial rings, whereas L. magnus Palmer, Reference Palmer1965, from the Elvinia Zone of Nevada (Palmer Reference Palmer1965, pl. 10, fig. 15), bears deeper pleural furrows, longer (exsag.) pleural fields (exsag.) and a more pronounced (sag.) median notch.

Unfortunately, the Rusconi collection lacks cranidia that could be assigned to L. obliquoanus, which prevents further comparisons. Rusconi (Reference Rusconi1958, p. 87, fig. 3b–d) tentatively linked the type pygidia of Cayupania obliquoana with a tumid cranidium that is herein more appropriately described as Onchonotopsidae? gen et sp. indet. (see below).

Figure 3

(a–c) Onchonotopsidae? gen. et sp. indet., fragmentary cranidium in dorsal (a), lateral (b) and anterior (c) views, MCNAM 21027 (illustrated previously with a sketch, Rusconi Reference Rusconi1958, fig. 3b–d), from Block 2 (lower Furongian; Paibian), Quebrada Oblicua, San Isidro area, Mendoza. (d–i) Cedaria puelchana Rusconi, Reference Rusconi1954a: (d, f) pygidium in dorsal (d) and lateral (f) views, MCNAM 21250; (e) cranidium, MCNAM 21246a, Cedaria cajonensis Rusconi, Reference Rusconi1958 holotype (not illustrated previously; erroneously cited as MCNAM 21296 by Rusconi Reference Rusconi1958, p. 91; see Cerdeño Reference Cerdeño2005); (g, i) pygidium in dorsal (g) and lateral (i) views, MCNAM 21246b (erroneously cited as MCNAM 21296 by Rusconi Reference Rusconi1958, p. 91; see Cerdeño Reference Cerdeño2005); (h) pygidium, MCNAM 21249; from Block 3 (upper Guzhangian), Quebrada Oblicua, San Isidro area, Mendoza. Scale bars = 4 mm.

Occurrence. One cranidium (MCNAM 21027), Quebrada Oblicua, Mendoza, La Cruz Olistoliths, Dunderbergia Zone, upper Paibian.

Remarks. Rusconi (Reference Rusconi1958) fully described a large cranidium from Block 2 that was cautiously assigned to Cayupania obliquoana (=Litocephalus obliquoanus, see above) (Rusconi Reference Rusconi1958, p. 87). However, the presence of a conspicuous bulbous glabella warrants a review of its affinities.

The glabella is covered with closely spaced fine granules. Unfortunately, the rear part of the cranidium is incompletely preserved, so it is not possible to determine the presence or absence of an occipital spine. In the main, the specimen exhibits several key features of Onchonotopsis Rasetti, Reference Rasetti1946 (type species, O. pergibba Rasetti, Reference Rasetti1946) (Rasetti Reference Rasetti1946; Rasetti in Harrington et al. Reference Harrington, Henningsmoen, Howell, Jaanusson, Lochman-Balk, Moore, Poulsen, Rasetti, Richter, Richter, Schmidt, Sdzuy, Struve, Tripp, Weller, Whittington and Moore1959; Palmer Reference Palmer1968; Westrop & Dengler Reference Westrop and Dengler2025) such as an ovate, strongly inflated glabella lacking lateral furrows, a short frontal area, and narrow (tr.) fixigenae; however, on the other hand, it differs by its divergent anterior facial sutures. Thus, open nomenclature is provisionally used for this material.

Type species. Cedaria prolifica Walcott, Reference Walcott1924, from the upper Guzhangian of Alabama, by original designation.

Occurrence. 200 m NW of Estancia San Isidro (Rusconi Reference Rusconi1954a; Tortello Reference Tortello2023); two cranidia and four pygidia (MCNAM 21246a, b, 21249–21252), Quebrada Oblicua, Mendoza, La Cruz olistoliths, upper Guzhangian.

Remarks. Rusconi (Reference Rusconi1958, p. 91) erected Cedaria cajonensis Rusconi, Reference Rusconi1958 based on a set of large specimens of Cedaria from Block 3 (=block with Cedaria) (Fig. 3d–i) showing perceptible lateral glabellar furrows, a well-developed preglabellar field that is longer (sag.) than the cranidial border, radiating prosopon ridges, strongly divergent anterior facial sutures, a narrow (tr.), long pygidial axis, five pairs of elongated pleural furrows, and a slender, poorly defined pygidial border. A supplementary glabellar furrow is sagitally extended from S1 to S2. Although Rusconi (Reference Rusconi1958) described the anterior cranidial border furrow as a continuous linear groove, fine preparation reveals indications of pits along its entire length.

All of these features accord with those of Cedaria puelchana Rusconi, Reference Rusconi1954a, from the upper Guzhangian (Cedaria prolifica Zone) of 200 m NW of Estancia San Isidro, Mendoza (Rusconi Reference Rusconi1954a, pl. 4, fig. 9; Tortello Reference Tortello2023, fig. 3.4–3.14); therefore, C. cajonensis is suppressed here as its junior synonym. Comparisons of C. puelchana with other species of Cedaria were provided by Tortello (Reference Tortello2023).