Clamorosaurus nocturnus Gubin, 1983

Werneburg, Ralf & Witzmann, Florian, 2024, The last eryopids: Clamorosaurus and Syndyodosuchus from the late Kungurian (Cisuralian, Permian) of Russia revisited, Fossil Record 27 (3), pp. 353-380 : 353-380

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 width of the supratemporal is striking; this bone is only 1.1 times longer than wide. Only in C. borealis the supratemporal is much wider than long (see below).

The parietals anteriorly approach the level of the posterior orbital margin, and the postparietals and tabulars are comparatively short. The tabular horn is modestly elongated (Th l / S l = 0.09), narrow and its rounded tip points posteriorly and slightly laterally. The width of the cheek is pronounced (W w / S l = 0.30) and is only exceeded by the relative cheek width in Onchiodon (Table 2 ). The squamosal is relatively narrow and the quadratojugal is very wide, especially in its anterior part. The quadratojugal reaches far posterior so that its posterior end comes to lie posterior to the squamosal and roofs the quadrate (Fig. 6 A, B ).

The exposure of the quadrate on the occipital surface of the cheek (Fig. 1 ) consists of a narrow strip of bone that is directed anteromedially between the squamosal and the quadrate ramus of the pterygoid. A boss-like protuberance at the ventral margin of the dorsal quadrate process like in Stenokranio or Glaukerpeton might have been developed (Fig. 3 B ). Quadratojugal foramina cannot be determined with certainty. Like in most adult eryopids, lateral line sulci are not present ( Witzmann et al. 2010; Werneburg et al. 2023).

Palate and braincase. From the palate, large parts of the vomers, palatines, ectopterygoids, pterygoids and the basal plate of the parasphenoid are preserved. Longitudinal ridges on the palatal bones are not developed. Immediately anterior to the level of the anterior vomerine tusks, the rounded posterior end of the anterior palatal fossae extends on the anterior part of the vomers (Fig. 4 D ) and probably on the dental shelf of the premaxilla.

The vomer is elongated and narrow. The smallest width of both vomers (= interchoanal width ICw / Sl = 0.22) is equal to the smallest width between the narial openings (internarial width) and nearly the same as the interorbital width. The posterolateral corner of the vomer encloses the anterior tip of the pterygoid as in Eryops . The suture between vomer and palatine is much more elongated than in C. borealis , Glaukerpeton and Actinodon . The short palatine is only slightly longer than wide. The ectopterygoid is elongated and c. 1.5 times longer than the palatine. Its posteriormost part is equal in width to the medially neighbouring pterygoid.

The dentition of palatine and ectopterygoid is interesting. The palatine bears a conspicuous fang anteriorly and a much smaller one posteriorly, which has the same size as the two fangs on the anterior part of the ectopterygoid. The fangs on the vomer are of equal or smaller size than those on the ectopterygoid. They are located on two separate circular tooth pits; the slightly larger one is located medial to the anterior edge of the choanae and has space for two small fangs. On the right vomer, only one tooth is preserved in this pit, but there is space for another one. Two teeth have been recorded on the left vomer. A further, slightly smaller tooth pit with one tooth is positioned medial to the choana at its midlength. Apart from C. nocturnus , this second tooth pit on the vomer is only known in C. borealis (here with a pair of fangs) and Syndyodosuchus .

The relatively small choana is of irregular outline, medially expanded and slightly longer than wide. The choanae of Glaukerpeton , Actinodon and Eryops are larger and more elongate, and in the case of Stenokranio about as long as wide (Fig. 15 ).

The pterygoid has a narrow palatinal ramus; its most anterior part forms a narrow, anteromedially directed tip, which may overlap the posterolateral corner of the vomer. The transverse flange of the pterygoid exhibits a low, angular expansion. In C. borealis , Onchiodon and Actinodon , the entire free lateral margin of the pterygoid is greatly expanded into a right-angled projection. The palatinal ramus and the elongated basipterygoid ramus are strongly curved; thus, the interpterygoid vacuities are extremely wide, especially in their anterior part. The orbitae are not concealed by the pterygoids in ventral view. These characters are shared with C. borealis but are unknown in other eryopids. The stereospondylomorph Intasuchus ( Konzhukova 1956; Werneburg et al. 2020) presents similar features, but especially the anteriorly widened interpterygoid vacuities in Clamorosaurus contrast with Intasuchus . Polygonal bony plates covering the interpterygoid vacuities are not preserved. Three larger bony plates are accumulated in the anterior part of the interpterygoid vacuities (Fig. 4 C, D ), which may represent remains of the epipterygoid. Similar bones are known from C. borealis and Syndyodosuchus (see below).

The basicranial articulation is firmly sutured (Fig. 4 C, D ). The cultriform process of the parasphenoid is generally narrow in contrast to O. labyrinthicus and Eryops , in which the process is swollen in its posterior half with convex lateral margins. The basal plate has a narrow rectangular shape like in Eryops and Syndyodosuchus . The ventral surface of the parasphenoidal basal plate has curved furrows for the carotid artery below the basipterygoid pockets, but their foramina lie more anterodorsally near the pockets. A large denticle field is developed between these furrows, which may taper anteriorly like in C. borealis to attain a triangular shape. Numerous denticles are present on the vomer, on the palatinal ramus of the pterygoid, partly on the palatine and probably on the ectopterygoid. The basioccipital and exoccipitals were apparently not ossified in this growth stage. The articular condyle of the quadrate is transversely expanded.

The visceral skeleton and mandibles are not preserved.

Postcranium. Few bones of the anterior part of the postcranial skeleton are associated with the skulls: ribs, clavicles, scapulocoracoids and ventral scales. One narrow rib and one rib with expanded proximal and distal ends are preserved. The clavicle has a relatively narrow ventral blade with remains of dermal sculpture (Fig. 5 F ). The scapulocoracoid (Figs 3 , 5 F ) has an angle of about 90 ° between the supraglenoid buttress and the anterior margin of the scapular blade. Such an angle is known in most Eryops specimens and Stenokranio (see discussion in Werneburg et al. 2023). This angle is less than 90 ° in Glaukerpeton and O. labyrinthicus .

Figures

Figure 1. Stratigraphic position of the Sheshminskian horizon (A) and geographical map with the position of the locations Inta and Pechora at the NW-margin of the Ural Mountains in the Komi Republic of Russia (B).

Figure 2. Reconstructed eryopid skull roof with measured distances. Abbreviations: aS w, anterior width of skull at level of maxilla-premaxilla sutures; H l, postorbital midline length of skull from level of posterior margins of orbits; H w, postorbital width of skull between lateral margins of supratemporals; IN w, minimum internarial width; IO w, minimum interorbital width; J w, transverse width of jugal at maximum lateral lacrimal extent of orbit; La l, maximum length of lacrimal; La w, maximum transverse width of lacrimal; mS w, midlength width of skull at midlength level of orbits; O l, maximum length of orbit; p, number of dermal skull pits or valleys per inch 2 (6.452 cm 2) mainly from frontal and jugal at midlength level of orbits; PO l, preorbital midline length of skull from level of anterior margins of orbits; Po l, maximum posterior length of postorbital from posteriormost extent of orbit; Po w, maximum transverse width of postorbital at contribution to orbital margin; pS w, maximum posterior width of skull at level of posterolateral margins of cheeks; S l, midline skull length; Th l, length of tabular horn region between levels of posterior tabular corner and occipital midline margin; W w, maximum transverse width of cheek from lateral margin of supratemporal anterior to otic notch.

Figure 3. Clamorosaurus nocturnus Gubin, 1983, skull roof in dorsal view, with scapulocoracoid, clavicle and ventral scales (A, B), holotype PIN 1582 / 1, from the Sheshminskian Gorizont (late Kungurian, Permian) of the Pechora River (Komi Republic, Russia). Abbreviations: cl, clavicle; f, frontal; j, jugal; l, lacrimal; n, nasal; p, parietal; pm, premaxilla; po, postorbital; pp, postparietal; prf, prefrontal; pt, pterygoid; ptf, postfrontal; q, quadrate; qj, quadratojugal; sc, scapulocoracoid; sq, squamosal; st, supratemporal; t, tabular; vs, ventral scales.

Figure 4. Clamorosaurus nocturnus Gubin, 1983, second specimen PIN 1582 / 4, with skull roof in dorsal view (A, B), and palate in ventral view (C, D), from the Sheshminskian Gorizont (late Kungurian, Permian) of the Pechora River (Komi Republic, Russia). Abbreviations: ap, anterior palatal depression; bp, basal plate of parasphenoid; ch, choane; cp, cultriform process; ec, ectopterygoid; ept, epipterygoid; f, frontal; faci, furrow for carotid artery; j, jugal; l, lacrimal; m, maxilla; n, nasal; pl, palatine; pm, premaxilla; po, postorbital; pt, pterygoid; ptf, postfrontal; qj, quadratojugal; sm, septomaxilla; sq, squamosal; v, vomer.

Figure 5. Clamorosaurus nocturnus Gubin, 1983, further specimens, an anterior skull (PIN 1582 / 6) with skull roof in dorsal view (A, B), and palatal remains in ventral view (C, D), basal plate of parasphenoid and clavicular blade of the holotype in ventral view (PIN 1582 / 1, E), and postcranial bones from an additional specimen (PIN 1582 / 2 a – b, F) with remains of the scapulacoracoid, clavicle and ribs, all from the Sheshminskian Gorizont (late Kungurian, Permian) of the Pechora River (Komi Republic, Russia). Abbreviations: ap, anterior palatal depression; bp, basal plate of parasphenoid; ch, choane; cl, clavicle; ec, ectopterygoid; faci, furrow for carotid artery; l, lacrimal; m, maxilla; ms, median suture; n, nasal; pl, palatine; pm, premaxilla; r, rib; sc, scapulocoracoid; sm, septomaxilla; v, vomer.

Figure 6. Clamorosaurus nocturnus Gubin, 1983, tentative reconstruction of the skull roof in dorsal view (A), and of the palate in ventral view (B). Abbreviations: ap, anterior palatal depression; bp, basal plate of parasphenoid; ch, choane; cp, cultriform process; ec, ectopterygoid; f, frontal; j, jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; pl, palatine; pm, premaxilla; po, postorbital; pp, postparietal; prf, prefrontal; pt, pterygoid; ptf, postfrontal; q, quadrate; qj, quadratojugal; sm, septomaxilla; sq, squamosal; st, supratemporal; t, tabular; v, vomer.

Figure 14. Comparison of the revised Russian eryopid skulls in dorsal and palatal view, Clamorosaurus nocturnus (A, B), Clamorosaurus borealis (C, D), Syndyodosuchus tetricus (E, F). Abbreviations: aci, foramen for carotid artery; bp, basal plate of parasphenoid; ch, choane; cp, cultriform process; ec, ectopterygoid; ept, epipterygoid; f, frontal; faci, furrows for carotid artery; j, jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; pl, palatine; pm, premaxilla; po, postorbital; pp, postparietal; prf, prefrontal; pt, pterygoid; ptf, postfrontal; q, quadrate; qj, quadratojugal; sm, septomaxilla; sq, squamosal; st, supratemporal; t, tabular; v, vomer.

Figure 15. Comparison of related eryopid skulls in dorsal view (A – F) and palatal view (G – L); (A, K) after Werneburg et al. (2023); (B, L) after Werneburg and Berman (2012); (C, G) after Sawin (1941); (D) after Werneburg (1997); (E, I) after Werneburg (2007); (F, J) after Boy (1991); (H) after Werneburg and Steyer (1999). Abbreviations: ch, choane; cp, cultriform process; ec, ectopterygoid; eo, exoccipital; f, frontal; j, jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; pl, palatine; pm, premaxilla; po, postorbital; pp, postparietal; prf, prefrontal; ps, parasphenoid; pt, pterygoid; ptf, postfrontal; q, quadrate; qj, quadratojugal; se, sphenethmoid; sm, septomaxilla; sq, squamosal; st, supratemporal; t, tabular; v, vomer.