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Clamorosaurus nocturnus Gubin 1983

Year: 2024
Type: other
Abstract: Clamorosaurus nocturnus Gubin, 1983 Figs 3, 4, 5, 6, 14 A, B Holotype. PIN 1582/1, consisting of the skull roof (skull length 18.2 cm), scapulocoracoid and ventral scales, together with undetermined bony remains, and a partly prepared section of the basal plate of the parasphenoid and the clavicle, both in ventral view. Other material. PIN 1582/4, consisting of the anterior part of a skull with the skull roof in dorsal and the palate in ventral view; PIN 1582/6, consisting of the anterior part of a skull with the skull roof in dorsal view and the fangs of ectopterygoid, palatine and vomer of the palate in ventral view; PIN 1582/2 a, consisting of a scapulacoracoid with ribs, PIN 1582/2 b representing a clavicle, and PIN 1582/2 c consisting of a possible humerus-fragment in two parts). Occurrence. All this referred material was discovered near the town of Pechora on the lower Pechora River (Komi Republic, Russia) in the Sheshminskian Gorizont (Ufimian), late Kungurian (Cisuralian, Permian). Diagnosis. C. nocturnus has no autapomorphies, but a unique combination of characters: (1) Density of sculpture pattern quantified as the number of pits per in 2 on frontal plus jugal range between 3.08 and 4.07, shared with C. borealis, Glaukerpeton and close to Syndyodosuchus, but in contrast to all other eryopids; (2) Premaxillary and maxillary teeth are small and circular in cross section, in contrast to C. borealis, O. labyrinthicus, and Eryops; (3) Teeth no. 8 and 9 are the largest in the premaxilla, in contrast to C. borealis and many other eryopids; (4) Tooth no. 6 is the largest in the maxilla, in contrast to C. borealis and many other eryopids; (5) Equal internarial and interorbital width, in contrast to C. borealis, Syndyodosuchus, Glaukerpeton, and E. megacephalus; (6) Narrow interorbital width, shared with C. borealis, Syndyodosuchus, Actinodon, and E. megacephalus; (7) Jugal very wide, shared with C. borealis, O. thuringiensis, and Eryops sp. from the Moran Formation (MCZ 1914; Werneburg 2008; Schoch and Milner 2014); (8) Septomaxilla is completely unsculptured and ventrally directed, shared with C. borealis, Eryops, and Glaukerpeton; (9) Short contact between jugal and prefrontal, shared with Syndyodosuchus, Glaukerpeton, Actinodon, and O. labyrinthicus, but in contrast to C. borealis, O. thuringiensis, and E. megacephalus; (10) Supratemporal wide, but longer than wide, in contrast to C. borealis; (11) No interfrontal, in contrast to Eryops and Osteophorus; (12) No lateral line sulci, in contrast to Glaukerpeton and Actinodon; (13) Interchoanal width is equal to internarial width, in contrast to C. borealis; (14) Short and wide palatine, only slightly longer than wide; (15) Ectopterygoid much longer than palatine; (16) Narrow basal plate of parasphenoid, in contrast to C. borealis, Onchiodon, Stenokranio and Glaukerpeton; (17) Cultriform process of parasphenoid longer than median length of vomer, shared with nearly all eryopids, but in contrast to C. borealis. Comparative description. Three incompletely preserved skulls with median lengths of 16 to 18 cm show the skull roof in dorsal view and parts of the palate in ventral view. They have complementary, congruent features, such as a small, dense dermal sculpture, small, almost oval orbitae, a very narrow interorbital region (IOw / Sl = 0.21), a very wide jugal, a wide lacrimal that reaches to the naris in front, and rather small teeth in the maxilla and premaxilla. Therefore, all these skulls belong to the same species. General skull morphology. The dermal sculpture of the dorsal surface of the skull roof corresponds to the relatively fine sculpture pattern known from some eryopids such as Clamorosaurus borealis, Syndyodosuchus tetricus and Glaukerpeton avinoffi (Werneburg and Berman 2012) (Table 1). It consists of a reticulated pattern of small pits and valleys separated by narrow ridges (Figs 1 – 3). The nasal, jugal and squamosal show much more radially directed ridges. The density of the sculpture pattern is quantified as the number of pits per in 2 (6.452 cm 2) on the frontal and jugal, which are typically well-preserved bones in eryopid skulls, and as a proportion of those counts to skull length. These intraspecific indices range between elements and specimens of C. nocturnus between 3.08 and 4.07, which are very similar in C. borealis, S. tetricus and G. avinoffi (Table 1). The dermal sculpture of the dorsal surface of the skull roof in other eryopid species has a much coarser pattern with indices from 0.4 up to 1.7. Higher indices between 1.2 and 4.3 occur only in the subadult Eryops (Table 1). The dorsal strutting pattern with large ridges on the skull roof is well developed (Fig. 6 A) and probably increased the mechanical stability of the skull (Sawin 1941; Boy 1990; Werneburg 2007; Schoch and Sobral 2021; Werneburg et al. 2023). A large longitudinal ridge extends from the lateral portion of the tabular and supratemporal to the postorbital. It then runs on the anterior skull table from the suture between prefrontal / frontal and on the lateral part of the nasal to the medial margin of the naris. Additional transverse ridges occur between the longitudinal ridges on frontals and nasals (Figs 3, 4 A, B). The areas between these ridges are depressed. Additionally, a short ridge on the jugal is traceable (Fig. 4 B). The degree of skull roof ossification appears to be relatively low and the bones may be intermediate between the normally thick bones as in most other eryopids and the 30–50 % thinner skull roof bones of Glaukerpeton (Werneburg and Berman 2012). The combination of the three known skulls of C. nocturnus allowed a tentative reconstruction of the skull roof in dorsal view and of the palate in ventral view (Fig. 6 A, B). The skull is slightly wider than long (Table 2; pS w / S l = 1.04). The lateral margin of the skull is convex in dorsal view. The snout margin is laterally constricted at the level of the naris like in Eryops megacephalus, Osteophorus and C. borealis. The postorbital region of the skull roof is relatively long (H l / S l = 0.26) and wide (H w / S l = 0.50) in contrast to that of E. megacephalus and Stenokranio. The preorbital skull is relatively elongate (PO l / S l = 0.57). The internarial and interorbital width are nearly equal (IN w / S l = IO w / S l = 0.21–22) as in many eryopids, but in contrast to Glaukerpeton in which the internarial width is smaller, and to E. megacephalus, C. borealis and S. tetricus with a smaller interorbital width (Table 2). The occipital margin of the skull roof is only slightly concave as in Onchiodon thuringiensis and C. borealis. The quadrate condyles lie distinctly posterior to the occipital condyles (Qc l / S l = 0.17; Table 2). The long oval orbits are relatively small compared to other eryopids (O l / S l = 0.16). Growth stage. The three skulls of Clamorosaurus nocturnus (PIN 1582/1, 1582/4 and 1582/6) clearly belong to adult animals, as indicated by the following features: (a) The dermal sculpture consists of a reticulated pattern of small pits and valleys separated by narrow ridges; (b) The quadrate condyles lie distinctly posterior to the occipital condyles; (c) The quadrate is ossified dorsally; (d) The orbits are relatively small compared to other eryopids; (e) The pterygoid has a pronounced transverse process; (f) The scapulocoracoid is well ossified (Figs 3, 5 F); (g) The skull length of 16–18 cm is relatively large and ranged in the middle-sized group in the family Eryopidae, and Actinodon and Onchiodon labyrinthicus have no larger skulls. However, the degree of ossification of the neurocranium indicates that the three specimens were early adults: (h) Sphenethmoid and basioccipital are not preserved and were probably not ossified in this stage. Skull roof. The interpremaxillary suture is short and accounts for 7.4 % of the midline length of the skull. The alary process of the premaxilla is wide and short. C. borealis and Actinodon have no alary process. The premaxillary tooth arcade has nine tooth loci (only six in C. borealis). The relatively small teeth have a circular cross-section, and only the two posteriormost teeth are slightly larger. This type of dentition contrasts with that of C. borealis, E. megacephalus and O. labyrinthicus, which consists of much larger teeth that are long-oval in cross-section. The maxilla has a relatively narrow dorsal shelf and is ventrally in contact with the quadratojugal. Its tooth arcade has about 25 tooth loci (only 21 in C. borealis). The teeth have a circular cross-section and they are relatively small. Only the sixth tooth is slightly larger, similar in size to the two larger ones of the premaxilla. This type of dentition contrasts with that of C. borealis, E. megacephalus and O. labyrinthicus, which has much larger teeth that are long-oval in cross-section. The circular naris is of similar proportional length as in Glaukerpeton or E. megacephalus, comprising 10 % of the midline length of the skull. The small septomaxilla is not sculptured (Figs 4 A, B, 5 A, B) and may be ventrally directed inside the naris (shared with Eryops). The posterior margin of the naris is clearly formed by the nasal, lacrimal and maxilla (Fig. 5 A, B). The lacrimal is roughly diamond-shaped. It is separated from the orbit by a short contact between jugal and prefrontal. The medial part of the lacrimal is wide (La w / La l = 0.49), and this bone participates in the posterolateral narial margin. The frontal is long and narrow like in most other eryopids and gets narrower in its posterior part where it is restricted by the medially expanding postfrontals. The jugal is proportionally wider (Ju w / S l = 0.22) than in all other eryopids apart from Eryops sp. (MCZ 1914) from the Moran Formation (Table 2). The postorbital is triangular in outline. The postfrontal and prefrontal clearly contact one another as in all eryopids. The prefrontal is anteriorly relatively wide. The
DOI: 10.5281/zenodo.14579663
Language: English
Subfield: Paleontology
Open Access status: green
OpenAlex ID: W6930694946
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