Clamorosaurus borealis Gubin 1983

Clamorosaurus borealis Gubin, 1983 Figs 7, 8, 9, 14 C, D Holotype. PIN 3950/1, consisting of the skull in dorsal and palatal view (skull length 15.3 cm) with associated isolated bones such as sphenethmoid, stapes and left quadrate. Other material. None. Occurrence. The holotypic material was found near the town of Inta (Komi Republic, Russia) in a limestone from the coal mine number nine of the Ufimian Intinskaya Svita, late Kungurian (Cisuralian, Permian) in 1961. Diagnosis. Autapomorphies: (1) Premaxilla with only six teeth, in contrast to nine to 15 premaxillary tooth loci in all other eryopids; (2) Maxilla with only 21 teeth, in contrast to 25 to 43 maxillary tooth loci in all other eryopids; (3) Supratemporal much wider than long; (4) Cultriform process of parasphenoid much shorter than median length of vomer. Synapomorphies with some other eryopids: (1) Density of sculpture pattern quantified as the number of pits per in 2 on frontal plus jugal range between 3.40 and 5.23, shared with C. nocturnus, Glaukerpeton and Syndyodosuchus, but in contrast to all other eryopids; (2) Premaxilla without alary process, shared with Actinodon; (3) Some teeth have a long-oval cross-section in labial-lingual direction, shared with O. labyrinthicus and Eryops; (4) Teeth four to six are the largest premaxillary teeth, in contrast to C. nocturnus and many other eryopids; (5) The third tooth is the largest in the maxilla, in contrast to C. nocturnus, and many other eryopids; (6) Lacrimal wide, its width is only exceeded in O. thuringiensis; (7) Internarial and interorbital width differ, shared with Syndyodosuchus, Glaukerpeton, and E. megacephalus, but in contrast to C. nocturnus; (8) Very narrow interorbital width, shared with C. nocturnus, Syndyodosuchus, Actinodon, and E. megacephalus; (9) Small orbits, only Syndyodosuchus has relatively smaller orbits; (10) Jugal wide, shared with C. nocturnus, O. thuringiensis, and Eryops sp. from the Moran Formation (MCZ 1914); (11) Septomaxilla is completely unsculptured and ventrally directed, shared with C. nocturnus and Eryops; (12) Elongated contact between jugal and prefrontal, shared with O. thuringiensis, and E. megacephalus; (13) No interfrontal, in contrast to Eryops and Osteophorus; (14) Tabular with elongated tabular horn, shared with Stenokranio and O. thuringiensis; (15) Quadrate condyles lie far posterior to the occipital condyles, only in E. megacephalus is the distance larger; (16) No lateral line sulci, in contrast to Glaukerpeton and Actinodon; (17) Interchoanal width wider than internarial width, in contrast to C. nocturnus; (18) Elongated and narrow palatine, much longer than wide, shared with Syndyodosuchus and Actinodon, but in contrast to C. nocturnus; (19) Ectopterygoid and palatine about equal in length; (20) Greatly expanded transverse flange of pterygoid into a right-angled projection, shared with Onchiodon and Actinodon and much more pronounced than in C. nocturnus or Syndyodosuchus. (21) Wide basal plate of parasphenoid, in contrast to C. nocturnus, Onchiodon, Stenokranio and Glaukerpeton; (22) Triangular denticle field, shared with Onchiodon. Comparative description. General Skull Morphology. The dermal sculpture of the dorsal surface of the skull roof corresponds to the fine sculpture pattern known from eryopids such as Clamorosaurus nocturnus, 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 on nearly all skull roof bones (Fig. 7 A, B). 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 both elements of C. borealis between 3.40 and 5.23, and on the prefrontal this ratio is 7.84 (Table 1). The dermal sculpture of the dorsal skull roof in other eryopid specimens consists of a much coarser pattern with indices ranging from 0.4 up to 1.7. Higher indices between 1.2 and 4.3 occur only in subadult Eryops (Table 1). The dorsal strutting pattern with large ridges on the skull roof is well developed (Figs 7 A, B, 9 A). 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. A transverse ridge connects the longitudinal ridges on the frontals, and anterior and posterior to it the surface of the frontals is depressed. The degree of skull roof ossification is probably relatively high and the bones may have the thickness commonly present in other eryopids with the exception of Glaukerpeton and C. nocturnus (see above). The well-preserved skull of C. borealis allows a tentative reconstruction of the skull roof in dorsal view and of the palate in ventral view (Fig. 9). The skull is slightly wider than long (Table 2; Fig. 6 B; pS w / S l = 1.08). The lateral margins of the skull are convex in dorsal view. The snout margin is laterally markedly constricted at the level of the naris like in Eryops megacephalus and Osteophorus. The postorbital region of the skull roof is relatively long (H l / S l = 0.25) and wide (H w / S l = 0.52). The preorbital skull is relatively elongate (PO l / S l = 0.60). The internarial and interorbital width differ from each other (IN w / S l = 0.27, IO w / S l = 0.21) with a smaller relative interorbital width. Both species of Clamorosaurus share with Actinodon (IO w / S l = 0.20–0.21) the narrowest interorbital region in eryopids. The occipital margin of the skull roof is only slightly concave. The quadrate condyles lie distinctly posterior to the occipital condyles (Qc l / S l = 0.22; Table 2) as in Eryops. The circular orbits are small compared to other eryopids (O l / S l = 0.14). Growth stage. The single skull of Clamorosaurus borealis can be interpreted as adult for the following reasons: (a) The dermal sculpture consists of a dense reticulated pattern of small pits and valleys separated by narrow ridges; (b) The quadrate condyles lie far posterior to the occipital condyles; (c) The quadrate is ossified dorsally; (d) The orbits are small compared to other eryopids. Admittedly, small orbits could also represent a taxon-specific character and not necessarily an ontogenetic one. In general, however, larval and juvenile temnospondyls have proportionally larger orbits than adults, and thus the small orbits in C. nocturnus support our interpretation; (e) the pterygoid bears a pronounced transverse process; (f) The epipterygoid is ossified with a large plate. With a skull length of 15 cm, C. borealis is a middle-sized eryopid similar to Actinodon and Onchiodon labyrinthicus. Skull roof. The interpremaxillary suture is moderately long and accounts for 11.0 % of the midline length of the skull. An alary process of the premaxilla cannot be discerned, and the only other eryopid without this process is Actinodon. Both premaxillaries are strongly curved, leading to a narrow snout with a strongly arched tooth arcade and a lateral constriction anterior to the maxilla. The premaxilla has only six tooth loci, whereas all other eryopids have nine to 15 premaxillary tooth loci (Table 3). Similar to the small orbits, it cannot be ruled out that this is an ontogenetic character since tooth number frequently increases in temnospondyl ontogeny from larvae to adults in the context of proportional snout elongation (see e. g., Witzmann 2005 b). However, this possibility is regarded as unlikely by us because (1) Boy (1990) did not document any increase of premaxillary teeth during ontogeny of Onchiodon labyrinthicus, and (2) the other characters listed here argue against a larval or juvenile state of the specimens under study. Only the first two small teeth and the following middle-sized tooth have a circular cross-section. Teeth number four to six are the largest ones and possess a long-oval cross-section in labial-lingual direction, shared with Eryops megacephalus and O. labyrinthicus. The maxilla has a slightly wider dorsal shelf than C. nocturnus and it is ventrally in contact with the quadratojugal. Its tooth arcade has only about 21 tooth loci in contrast to all other eryopids having 25–43 tooth loci. All maxillary teeth are much smaller than the largest premaxillary teeth but are similar in size to the smallest premaxillary teeth. The 3 rd posterior maxillary tooth is the largest one and causes a small lateral expansion of the skull margin, but this tooth is slightly smaller than the third tooth of the premaxilla. The maxillary teeth are mostly circular in cross-section with few exceptions on the right maxilla which possess a long-oval cross-section in labial-lingual direction. The circular to oval shaped naris is relatively small as in O. labyrinthicus, its length comprising 8 % of the midline length of the skull. The small septomaxilla is not sculptured (Fig. 7 A, B) and lies ventrally directed inside the naris (shared with Eryops and C. nocturnus). The posterior margin of the naris is clearly formed by the nasal, lacrimal and maxilla (Fig. 9 A). The lacrimal is triangular with a wide posterior part (La w / La l = 0.54). It is separated from the orbit by an elongated contact between jugal and prefrontal. The frontal is narrow like in most other eryopids and does not reach anteriorly to the level of the anterior ends of prefrontal and jugal. The jugal is wide (Ju w / S l = 0.20) and proportionally only slightly narrower than in C. nocturnus. Therefore, the width of the skull at its midlength is similarly large in both species of Clamorosaurus (mS w / S l = 0.98), comparable to O. labyrinthicus (mS w / S l = 1.00). The postorbital is triangular in outline. The postfrontal and prefrontal clearly con