Discosauriscus, KUHN, 1933

Klembara, Jozef, Mikudíková, Marika, Štamberg, Stanislav & Hain, Miroslav, 2020, First Record Of The Stem Amniote Discosauriscus (Seymouriamorpha, Discosauriscidae) From The Krkonoše Piedmont Basin (The Czech Republic), Fossil Imprint 76 (2), pp. 243-251 : 246-249

Discosauriscus pulcherrimus ( FRITSCH, 1880)

D i a g n o s i s. Discosauriscus pulcherrimus is characterized by three diagnostic features: 1) the posterior ramus of the prefrontal is anteroposteriorly shorter than the anterior ramus of the postfrontal and both rami meet at the level of the anterior, middle third of the frontal length; 2) the ventrolateral ramus of the postorbital is narrow and pointed and lies anteriorly to the wedge-shaped dorsomedial ramus of the jugal; and 3) the rows of small densely arranged denticles diverge anteromedially and anterolaterally from the mid-width of the ventral surface of the palatal ramus of the pterygoid.

M a t e r i a l. G 151 – disarticulated specimen ( Text-fig. 2a ) deposited in the Museum of Eastern Bohemia, Hradec Králové, the Czech Republic.

L o c a l i t y a n d h o r i z o n. Krkonoše Piedmont Basin (the Czech Republic), Upper Kalná Horizon, village Arnultovice (3 km north of the town of Hostinné).

D e s c r i p t i o n. In the following description, the bones, which are identifiable and crucial for determination of the here investigated specimen, are described and figured ( Text-figs 2–4 ).

Skull roof. Both frontals and right postfrontal are preserved in ventral view, partially as the bones and partially as impressions of their ornamented surfaces ( Text-fig. 2b, c ). The ornamentation of the frontal consists of grooves and ridges radiating from the ossification centre lying at about mid-length of the bone. The ventral wall of the medial portion of the left frontal is well preserved. Its medial margin bears an anteroposteriorly long, narrow articulating surface for the ventral lamina of the right frontal ( Text-fig. 2b ). The medial margin of the left frontal is undulated slightly posteriorly to the mid-length of the bone. Only a small portions of the ventral wall of the right frontal are preserved ( Text-fig. 2c ). The posterolateral portion of the right frontal is missing, but its impression indicates that its lateral margin ran posteromedially. The medial margin of the right frontal is distinctly undulated and matches the undulated margin of the left frontal. The posterior two thirds of the left prefrontal with a distinct arch-like orbital margin is preserved in ventral view ( Text-fig. 2c ). The right intertemporal is well preserved ( Text-fig. 2d ). In addition to its straight lateral margin, the bone is approximately oval in shape. The ornamented surface is well preserved. Its ossification centre consists of tubercles and pits located around the central portion of the bone; from here, the ridges and grooves radiate towards the periphery of the bone. The right parietal is perfectly preserved (Textfig. 2e). Its ornamentation consists of grooves and ridges which radiate from the ossification centre located around the central portion of the bone. The right supratemporal is anteroposteriorly elongated and a rectangular shape (Textfig. 2f). Its posterolateral corner extends into a distinct process. The ornamented surface is preserved only on the medial margin of the bone. The left tabular is well preserved in dorsal view ( Text-fig. 2b ). The right tabular was segmented and a virtual 3D model produced ( Text-fig. 3a, b ). In both tabulars the ornamented surfaces, smooth occipital flanges and tabular processes are well preserved. On the ventral surface of the tabular, the arcuate crest is distinctly developed ( Text-fig. 3b ). The right postparietal is completely preserved. Because it is completely embedded in the sediment, it was also digitally removed (Textfigs 2a, 3c, d). On its dorsal surface, the broad anterior and medial ventral lamellae are well preserved. Posterior to the ornamented surface, the smooth, mediolaterally elongated and anteroposteriorly short occipital flange is present. The right postorbital is well-preserved ( Text-figs 2e , 3e, f ). It has a well-developed, raised orbital margin. Below this margin, a shallow groove runs in a mediolateral direction. This groove probably represents a sensory groove (cf. Klembara 1994, 1995, 1996). The ventrolateral process is pointed. The medial process is more robustly constructed and has a short anteroposterior suture with the postfrontal. The posterior process is slightly mediolaterally expanded and its posterior tip rounded. However, the posterior portion of this process in not well preserved. The left jugal was digitally removed from the sediment and is completely preserved ( Text-figs 2a , 3g, h ). The suborbital ramus is long, narrow and anteriorly pointed; the dorsomedial ramus is much shorter and wedge- shaped. Its anterior and posterior margins bear overlapped areas (ventral lamellae). The anterior ventral lamella was overlapped by the tip of the ventrolateral process of the postobital. The posterior ventral lamella was overlapped by the squamosal ( Text-fig. 3e, f ).

Palate. Two palatal elements are preserved ( Text-fig. 2g, h ). The completely preserved parasphenoid is exposed in ventral view ( Text-fig. 2g ). The parasphenoidal plate extends anteriorly as a triangular, pointed wedge-like process extending anteriorly and slightly ventrally. The process lies anteriorly to the level of the anterior portions of the basipterygoid processes. The surface of the wedgelike process bears several short rows of small denticles. The cultriform process is of triangular shape. Its broad posterior portion gradually narrows to a pointed anterior portion. The ventral surface of the posterior half of the cultriform process bears rows of small denticles radiating from its posterior portion anteriorly and laterally. The endochondral basipterygoid processes lie at a level immediately posterior to the cultriform process. The posterolateral processes are stout and extend laterally and slightly posteriorly. The posteromedian process is rounded and bears a sharp straight median ridge.

Most of the palatal ramus of the right pterygoid is preserved ( Text-fig. 2h ). It shows a typical, autapomorphic feature of Discosauriscus pulcherrimus: the rows of small densely packed denticles diverging anteromedially and anterolaterally from mid-width of the ventral surface of the palatal ramus of the pterygoid. The rows of the denticles are straight, densely arranged and divided by narrow grooves.

Lower jaw. Partial dentary and several other lower jaw elements are also present, but they are fragmentary (Textfig. 2a).

Postcranial skeleton. A sequence of poorly preserved anterior vertebrae is present ( Text-fig. 4a ). Only the crescent pleurocentra are identifiable in the posterior presacral portion of the vertebral column ( Text-fig. 4f ). Along the right side of the vertebral column, the ribs are well preserved. The anterior ribs are short, but more posteriorly become longer and progressively more spatulate. Still further posteriorly the ribs become progressively narrower and longer, and then again shorter ( Text-fig. 4a, f ).

The pectoral girdle is almost completely preserved (Textfig. 4d). The interclavicle consists of a wide anterior plate and narrow posterior stem. The anterior portion of the stem is widened. The ventral surface of the anterior plate bears large areas for the ventral plates of the clavicles. Between these areas, the surface of the anterior plate bears radially diverging bony strips. The left ( Text-fig. 2a ) and right (Textfig. 4d) clavicles are well-preserved. Their ventral plates are wide, and the ascending processes are narrow and pointed. The rod-like cleithra are slender ( Text-fig. 4d ). The right, crescent-shaped scapula is well-preserved ( Text-fig. 4d ). The supraglenoid buttress of the scapula is visible in its ventromedial portion. The scapula is of about the same length as the humerus ( Text-fig. 4a ). The right humerus is robustly constructed ( Text-fig. 4a, b ). It is possible to recognize the ectepicondyle and the entepicondyle with a large distally opened entepicondylar foramen ( Text-fig. 4b ). The radius and ulna are also preserved; they are slightly shorter than the humerus. The left manus is incomplete and only the metacarpals and several fragments of the proximal phalanges are recognizable ( Text-fig. 4c ).

The left hind limb is represented by incompletely preserved femur, tibia and fibula ( Text-fig. 4e ). All three elements are dorsoventrally compressed.

A small group of scales is preserved close to the pelvic girdle. The scales are small, more-or-less rounded elements ( Text-fig. 4g ).

C o m p a r i s o n s a n d c o n c l u s i o n. We can conclude that the specimen described here represents the species Discosauriscus pulcherrimus. There are two diagnostic features which allow us to assign the specimen to this species:

(1) The presence of the narrow pointed ventrolateral

process of the postorbital, the tip of which lies anteriorly

to the tip of the wedge-shaped dorsomedial process of

the jugal. Such morphology of the postorbital and jugal

processes is typical for D. pulcherrimus ( Klembara

1997, Klembara and Mikudíková 2019). In contrast,

in D. austriacus ( MAKOWSKY, 1876) the dorsomedial

process of the jugal is anteroposteriorly broad and

has an anteroposteriorly running suture with the

anteroposteriorly broad ventrolateral process of the

postorbital ( Klembara 1997).

(2) The rows of small denticles diverge anteromedially

and anterolaterally from the mid-width of the ventral

surface of the palatal ramus of the pterygoid. In contrast,

in D. austriacus there are more-or-less prominent ridges

covered with small denticles which radiate from the

posterior portion of the ventral surface of the palatal

ramus of the pterygoid ( Klembara 1997). The ridges are

divided by deep wide grooves.

Furthermore, we can conclude that Discosauriscus pulcherrimus is recorded in three basins in the Czech Republic: the Intrasudetic Basin, Krkonoše Piedmont Basin and Boskovice Basin. Discosauriscus pulcherrimus is rare in the Boskovice Basin where the dominant species is D. austriacus ( Klembara and Meszároš 1992, Klembara 1997, Klembara and Bartík 2000, Klembara and Mikudíková 2019). The sediments with the fauna of the Upper Kalná Horizon ( Opluštil et al. 2016) lie close to the locality in Arnultovice, and also in the environs of the villages Horní Kalná and Klášterská Lhota ( Štamberg 2014). The type of sediments and composition of the fauna of the Upper Kalná Horizon are very similar to the Ruprechtice Horizon of the Olivětín Member present in the Intrasudetic Basin. The occurrence of D. pulcherrimus in both horizons, and in Kochov and Bačov horizons of the Boskovice Basin, confirm the stratigraphic correspondence of these horizons. New radioisotopic data ( Opluštil et al. 2016) from overlying ignimbrites in Tatobity (296.4 ± 0.08 Ma; Text-fig. 1b ) in the Chotěvice Formation of the Krkonoše Piedmont Basin suggest that the age of the Upper Kalná Horizon is Asselian, similar to that of the Olivětín Member of the Intrasudetic Basin and the Kochov and Bačov horizons of the Boskovice Basin. Schneider and Werneburg (2012) and Schneider et al. (2019) interpreted the Ruprechtice Horizon of the Olivětín Member, using different biostratigraphical scales (based on amphibians and insects), to be of Sakmarian to Artiniskian age. Specimens of D. pulcherrimus are most abundant in the basins in Germany ( Werneburg 1985, 1988, 1989, Boy 2007). We can also conclude that D. pulcherrimus is restricted to the early Permian basins in central and western Europe.

Figures

Text-fig. 2. Discosauriscus pulcherrimus (FRITSCH, 1880). a: specimen G 151, cranial and postcranial skeleton (for details of postcranial skeleton, see Text-fig. 4) with highlighted virtual 3D models of postparietal and jugal (cf. Text-fig. 3c, d and 3e, f) originally embedded in sediment, b: frontal, c: frontal and prefrontal, d: intertemporal,e:parietal andpostorbital,f: supratemporal and clavicle, g: parasphenoid, h: pterygoid. Abbreviations: ar.s. – articulating surface, CL – clavicle, cult. pr. – cultriform process, DE – dentary, FR – frontal, IT – intertemporal, JU – jugal, l. j. – lower jaw, or.m. – orbital margin, pal. ram. – palatal ramus, pl. pr. – posterolateral process, PO – postorbital, POFR – postfrontal, PP – postparietal, PRFR – prefrontal, ST – supratemporal, TAB – tabular.

Text-fig. 3. Discosauriscus pulcherrimus (FRITSCH, 1880), G 151. a–h: 3D virtual models of the selected dermal cranial bones; a, b: right tabular in dorsal (a) and ventral (b) views, c, d: right postparietal in dorsal (c) and ventral (d) views, e, f: right postorbital in dorsal (e) and ventral (f) views, g, h: left jugal in dorsal (g) and ventral (h) views. Abbreviations: cr. arc. – arcuate crest, oc. fl. – occipital flange, pr. tab. – tabular process, tr. rid. – transverse ridge.

Text-fig. 4. Discosauriscus pulcherrimus (FRITSCH, 1880), G 151. a: detail of the postcranial skeleton, b: left humerus, ulna and radius,c: right metacarpals,radius and ulna,d: pectoral girdle, e: hind limb elements, f: posteriormost presacral andsacral portion of the axial skeleton, g: imprints of scales in the posterior presacral region. Abbreviations: CL – clavicle, CTH – cleithrum, ect. – ectepicondyle, ent. – entepicondyle, ent.f. – entepicondyle foramen, FE – femur, FI – fibula, HU – humerus, ICL – interclavicle, im. of sc. – imprints of scales, met. – metacarpals, PC – pleurocentrum, sg.b. – supraglenoid buttress, R – ribs, RA – radius, RA+UL – radius and ulna, SC – scapula, TI – tibia, UL – ulna.

Text-fig. 1. a: simplified geological map of the Krkonoše Piedmont Basin with position of the locality in Arnultovice (see asterisk; coordinates 50° 33′ 58.599″ N; 15° 43′ 18.873″ E). After Blecha et al. (1997). b: position of the finding locality Arnultovice “Track in ravine on the edge of the forest” in idealised section of the Permian sediments of the Krkonoše Piedmont Basin. Locality Arnultovice and dating of overlying ignimbrites in Tatobity are indicated. After Opluštil et al. (2016), based on data in Prouza and Tásler (2001), modified here. c: detail of the outcrop “Track in ravine on the edge of the forest” near Arnultovice with 40–50 cm thick massive badly cleavable pinkish dolomitic limestone (L) and laminated calcareous claystone (C) with fauna.