Barschichthys ruedersdorfensis, Arratia & Schultze, 2024

Arratia, Gloria & Schultze, Hans-Peter, 2024, The oldest teleosts (Teleosteomorpha): their early taxonomic, phenotypic, and ecological diversification during the Triassic, Fossil Record 27 (1), pp. 29-53 : 29

Barschichthys ruedersdorfensis sp. nov.

Figs 7 , 8 , 9

Diagnosis.

Same as family diagnosis.

Derivatio nominis.

The names of the family and of the genus are dedicated to Mr. Enrico Barsch, who from an early age (ca. 15 years old) began to collect in the mine of Rüdersdorf, which is characterized by unique but few fossils in durable, hard-to-work stone. Thus, after years of search and careful work, Mr. Barsch has gathered an important collection studied herein and he also donated part of the collection to the Museum of Natural History (MB) in Berlin.

Type material.

Holotype. MB. f. 19907, a well-preserved skull roof including sensory cephalic cranial system and ornamentation.

Paratypes. MB. f. 19908, a well-preserved skull roof including ornamentation. MB. f. 19909, specimen of about 50 mm standard length, preserving the lateral view of the head and part of the trunk, which is interpreted as belonging to the same species due to the orbital region that is expanded anteriorly and broadly expanded posteriorly (though broken), as well as having the same ornamentation as in the holotype and paratype.

Provenience.

Opencast mine in Rüdersdorf, 25 km east of the center of Berlin, Germany.

Age.

Lower Middle Triassic, lower Anisian (middle Muschelkalk).

Description.

The head and anterior part of the body of MB. f. 19909 provide information on cranial bones and the pectoral girdle and their relationships and on the scales of the anterior body (Fig. 8 ). Patchy regions covered with tubercles are badly preserved on some of the lateral head bones and some scales. The head has its anterodorsal profile almost rounded, and the long lower jaw is slightly protruding anteriad (Fig. 9 ). Although the skull roof of the specimen is partially destroyed showing parts of left and right broken bones, it is evident that the head at the level of the extrascapulars is deeper than long. The diameter of the orbit is small, ca. 25% of the head length. Specimens MB. f. 19907 and MB. f. 19908 differ in the distance between orbits or mid orbital region width (PORW), but they are interpreted here as belonging to the same species because they share some unique features such as lacking the nasal region (NRL) of the skull roof plate, having an expanded and undulated anterior margin of the skull roof, and a similar postorbital region structure and proportions and sharing the same characteristic ornamentation. The difference in the mid-orbital region width may indicate sexual differences, a hypothesis that should be tested when more specimens become available.

Skull roof bones. Specimen MB. f. 19907 is a nicely preserved skull roof of ca. 19 mm long and 14 mm width at the postorbital region, with all dermal bones fused into a large, characteristically-shaped plate (Fig. 7 ), with the exception of the rostral and nasal bones that are not preserved. Still, some incomplete suture lines can be observed. Posteriorly, remains of a lateral extrascapula and a median extrascapula are preserved. The skull roof plate is expanded anteriorly, ending on a broadly undulated or lobated margin and expanding posteriad, reaching its maximum width at the supratemporotabular [= dermopterotic] level and ending in a gently curved line. The skull roof looks like a flat plate; however, the first impression is deceptive, because the lateral margins on the anterior part of the plate are lateroventrally inclined, with the mid-section of the parietal regions of the plate, slightly higher than the lateral orbital margins; the lateral margins of the postorbital region are gently inclined lateroventrally. Most of the skull roof is formed by the orbital region whose length is about 58% of its total length. The small triangular nasal region (Figs 1 , 3 ) present in Pseudopholidoctenus gen. nov. is absent here, but the anterior margin is broad; it is ca. 150% of the midregion of the orbital width. Because of the position of the supraorbital sensory canal on the skull roof plate lying closer to the midregion than to the lateral margins, there is the possibility that the nasals were very broad bones, joining at their medial margins and that the rostral bone was anterior to the nasals.

The skull roof (Fig. 7 ) does not show complete sutures separating bones, but there is a tenuous incomplete suture where both parietals [= frontals] meet, and another tenuous and incomplete suture separating partially the parietal and postparietal regions. Unlike other Triassic teleosteomorphs, a small oval fontanel separates left and right halves of the skull plate anteriorly in one skull roof, but it is almost closed in another specimen. As in Pseudopholidoctenus germanicus gen. et sp. nov., the parietal region would be the largest component of the skull roof, forming the whole orbital region and extending into the postorbital region. The lateral margins of the plate at the supratemporotabular region are ventrolaterally expanded and carry the otic canal, which is incompletely preserved. There is no evidence of a supraoccipital bone. Suturing with the posterior margin of the plate, there are pieces of the lateral extrascapulae and a median extrascapula preserved (Figs 7 , 9 ). Their anterior margin is smooth and not presenting the so-called thick “roll-over” that characterizes the extrascapulars in pholidophorids, which have only two extrascapulars, not three, as in the case of this fish.

The anterior nasal region of the plate is absent in this fish (compare Fig. 1 and Fig. 7 ), an interpretation based on other pholidophorids and teleosteomorphs with the region in situ. The broad anterior margin of the skull plate would articulate with the nasal bones, but only one nasal is incompletely preserved, forming an angle of almost 90 degrees with the parasphenoid. The relationship among the anterior margin of the plate, nasals, and rostral (not preserved) is unknown. Due to its size and position, the nasal bone would be part of the anterior region of the circumorbital region. The posterolateral corner of the orbital region is the area corresponding to the autosphenotic or sphenotic, which in this case, is fused to the parietal laterally and supratemporotabular [= dermopterotic] posteriorly.

The surface of most of the skull roof is covered by tubercle-like ornamentation that cannot be described properly due to irregularities in shape and position of the tubercles; however the ornamentation seems to be lacking in the anterior lobated region of the plate.

The supraorbital sensory canal (Fig. 7 ) and otic canal are visible in certain regions where the ornamentation is not preserved. No sensory pores opening on the surface have been observed. Only discontinuous sections of the middle pitline (Fig. 7 ) are visible on the postparietal plus supratemporotabular region; these are very difficult to observe because of the density of the ornamentation in the isolated skull roof plates, and the surface is damaged in MB. f. 19907 and MB. f. 19909.

Braincase. The braincase is covered by bones, and only sections of the interorbital septum and parasphenoid (Fig. 9 ) are preserved. A posterior section of the interorbital septum covers half the orbit in specimen MB. f. 19909. A section of the ascendent process of the parasphenoid can be observed in this specimen. Teeth or their sockets are not observed, so they are interpreted as absent. Posteriorly, the parasphenoid expands dorsally, but it is laterally covered by the suborbital so that the extension of the ascendent process is unknown. There is another ventrolateral extension that could be an incompletely preserved basipterygoid process.

Circumorbital bones and suborbital region. The description is based on MB. f. 19907 with the circumorbital ring partially preserved (Fig. 9 ) and includes infraorbitals 1 to 3 and the dermosphenotic. There is no evidence of supraorbital bones. Infraorbital 1 is a large, oval-shaped bone, slightly expanded anterodorsally. Infraorbital 2 is short and triangular-shaped. Infraorbital 3 is a large bone slightly rectangular-shaped and extending below the suborbital, reaching the opercular region. Infraorbitals 4 and 5 are not preserved, but remnants of an incomplete dermosphenotic are preserved in MB. f. 19908 and MB. f. 19909. One large, rectangular-shaped suborbital is surrounded by the dorsoposterior infraorbitals anteriorly (not preserved), the opercle posteriorly, and infraorbital 3 ventrally. The trajectory of the infraorbital canal can be seen in infraorbitals 1-3, but no branches or pores are visible.

Upper jaw. The maxilla and supramaxillae are preserved. An enlarged, narrow premaxilla is preserved as an imprint. The maxilla (Fig. 9 ) is moderately long, reaching just below the posterior margin of the orbit. However, it is unclear how the posterior margin of the maxilla ended, because the maxilla is broken at its posterior margin. Its anterior articular process is short and narrow in comparison to the maxillary blade that is narrow anteriorly and expands posteriad, with the posterior margin being almost double the depth of the anterior blade. The oral margin (at least at its posterior half) carries small conical teeth; some of these teeth are covered by the oral margin of the bone, but they are seen throughout the bone. The posterior supramaxilla (Fig. 9 ) is a large, oblong bone that covers about half of the posterior part of the dorsal margin of the maxilla. Below the anterior end of the supramaxilla, there is a tiny bone that is interpreted here as the anterior supramaxilla. The maxilla and supramaxillae are covered with elongate lines of ganoine, giving both bones a striated aspect.

Lower jaw. The lower jaw (Fig. 9 ) is an elongate bone, with a curved ventral margin, partially exposed below the maxilla, with its posterior region poorly preserved and extending posterior to the maxilla. Consequently, the articulation between lower jaw and suspensorium was posterior to the posterior margin of the orbit. The limit between the dentary and angular is not preserved as well as the trajectory of the mandibular canal. At least, in the posterior part of the jaw, some ridges covered with ganoine are preserved.

Opercular bones. The opercle, subopercle, fragment of the preopercle, and an interopercle (Fig. 9 ) are preserved. The opercle is slightly larger than the subopercle (with its dorsal margin broken; Fig. 9 ) and characteristically shaped. Its suture with the subopercle is oblique. The broad subopercle has an almost oblique ventral margin, which becomes slightly rounded posteriorly; its small anterodorsal process is broken and is anteriad directed. The preopercle is represented by some pieces so that a description is not possible, except to propose that the bone was short dorsally because of the position and relationships between the suborbital and opercle. The interopercle is preserved below the preopercle and interopercle, so that it is possible to assume that it was an elongate bone.

Branchiostegal rays and gular plate. Remnants of a few, narrow branchiostegal rays are preserved below the interopercle (Fig. 9 ). Below the posterior part of the lower jaw and opercular region, two elongate bones are preserved, and because of their position, they can be interpreted as being median bones. Thus, these are interpreted here as possibly two gular plates (Fig. 9 ).

Pectoral girdle and fin. It is unclear if one of the scale-like bones that is broken posterior to the extrascapular bones could be interpreted as a large posttemporal, having a medial position to the supracleithrum (Fig. 9 ). The dorsal part of the supracleithrum is partially exposed posterodorsal to the opercle. The cleithrum is a long bone whose ventral part is preserved, but the surface of its dorsal, narrower section is partially destroyed. The bone lacks a well-pronounced curvature and extends ventrally below the interopercle and branchiostegal rays, so that it is not possible to observe whether a clavicle was present anteriorly. Remains of the serrated appendage are preserved along the medial, ventral section of the bone. Three scaly types of postcleithra (Figs 9 , 10 ) are present. The first one is the longest of the series and the second one is somewhat oval shaped. Postcleithrum 2 has serrations at its posterior border, but since postcleithra 1 and 3 have their posterior margin poorly preserved, it is unknown whether more serrations were present. There are remains of ornamentation on the lower part of postcleithrum 3 that are shown in Fig. 10 .

Posterior to the posteroventral curvature of the cleithrum, a few broken rays (Fig. 10 ) are present, but their poor preservation does not allow a description.

Scales. The ganoid type of scales covering the body seem to be thick. There is not a distinct row of scales (Fig. 10 ) carrying the lateral line that can be described as significantly deeper than the next ventral body scale row; however, there is a significant difference between the lateral line scales and the dorsal series of scales that are smaller. The scales carrying the lateral line and those just above and below are rectangular, with short serrations at their posterior margin that are mostly destroyed. Ventrally, the series of scales become smaller and oval. In the ventral midline, or close to it, below the pectoral girdle and pectoral fin, some larger and oval-shaped scales or scutes are present (Fig. 10 ). Some of them still have preserved rounded or elongate tubercles of ganoine on their surface.

Teleosteomorpha Arratia, 2001

Family incertae sedis

Figures

Figure 1. Pholidophorid skull roof illustrating possible measurements. See text for explanation.

Figure 3. Pseudopholidoctenus germanicus gen. et sp. nov. (holotype MB. f. 18641) from Ruedersdorf, near Berlin, Germany (central European Basin; Germanic Basin). A. Photograph of skull roof. B. Interpretative drawing. Abbreviations: a. pl, anterior pitline; m. pl, middle pitline; ot. c, otic canal; pa + ppa + asp + stt [= fr + pa + asp + dpt], parietal + postparietal + autosphenotic + supratemporotabular [= frontal + parietal + autosphenotic + dermopterotic]; ppa. b, postparietal branch; p. pl, posterior pitline; sor. c, supraorbital canal; sp, pore of sensory canal. Scale bar: 1 mm (A).

Figure 7. Barschichthys ruedersdorfensis gen. et sp. nov. from Ruedersdorf, near Berlin, Germany (central European Basin; Germanic Basin). A. Photograph of skull roof (holotype MB. f. 19907). B. Interpretative drawing. C. Photograph of skull roof (MB. f. 19908). D. Interpretative drawing. Abbreviations: dsp, dermosphenotic; d. dsp, displaced dermosphenotic; ep, epiotic; fon, anterior cranial fontanel; i. s, incomplete suture; m. exc, median extrascapula; m. pl, middle pitline; ot. c, otic canal; pa + ppa + asp + stt [= fr + pa + asp + dpt], parietal + postparietal + autosphenotic + supratemporotabular [= frontal + parietal + autosphenotic + dermopterotic]; sor. c, supraorbital canal. Scale bars: 5 mm.

Figure 8. Barschichthys ruedersdorfensis gen. et sp. nov. (MB. f. 19909) from Ruedersdorf, near Berlin, Germany (central European Basin; Germanic Basin) illustrating head and anterior part of trunk in lateral view. Scale bar: 5 mm.

Figure 9. Barschichthys ruedersdorfensis gen. et sp. nov. from Ruedersdorf, near Berlin, Germany (central European Basin; Germanic Basin). Drawing of skull roof (MB. f. 19909). Hatched marks represent areas that are destroyed or too poorly preserved to allow a description. Abbreviations: b. dsp, broken dermosphenotic; b. na, broken nasal bone; b. pop, broken preopercle; br. r, branchiostegal rays; br. skr, broken skull roof; cl, cleithrum; ent, entopterygoid; exc, extrascapulae; gu?, gular plates?; io 1 - 3, infraorbitals 1 - 3; iop, interopercle; lj, lower jaw; op, opercle; orb, incomplete orbital septum; par, parasphenoid; pcl 1 - 3, postcleithra 1 - 3; pmx, premaxilla; ptt, posttemporal; sc, scale; smx 1 - 2, supramaxillae 1 - 2; sob, suborbital; sop, subopercle.

Figure 10. Barschichthys ruedersdorfensis gen. et sp. nov. from Ruedersdorf, near Berlin, Germany (central European Basin; Germanic Basin). Drawing of a section of the lateral trunk illustrating mainly scales and postcleithral bones (MB. f. 19909). Abbreviations: or, ornamentation (tubercles); pcl 1 - 3, postcleithra 1 - 3; pec. r, broken pectoral rays; sc, scales; scl, supracleithrum. Arrows point to large oval scales or scutes.