Palaeobatrachus diluvianus

Roček, Zbyněk, 2016, “ Lost ” And Rediscovered: Holotype Of Palaeobatrachus Diluvianus (Goldfuss, 1831), Fossil Imprint 72 (1 - 2), pp. 45-52 : 48-49

of Palaeobatrachus diluvianus ( GOLDFUSS, 1831)

The holotype specimen is a natural cast of the dorsal side of an almost complete, articulated skeleton of an adult ( Text-fig. 1 ; see also Goldfuss 1831: pl. 12, fig. 1; Meyer 1860: pl. 18, figs 1, 2), which is now deposited in the type collection of Steinmann-Institut für Geologie, Mineralogie und Paläontologie, Friedrich-Wilhelms-Universität, Bonn, Germany, as STIPB-Goldfuss-1343. Since Goldfuss explicitly referred in his description to this particular specimen, and because other specimens from the type series were juveniles or tadpoles, it can be implied that the holotype was fixed by monotypy (ICZN, Art. 73.1.2). It originates from the Late Oligocene (MP30, Neochattium; Mai 1995), from a now-abandoned opencast browncoal mine at Orsberg near Erpel (50°35'23.63"N; 7°14'47.15"E) ( Text-fig. 5 ).

Both premaxillae are preserved as imprints, but details (such as number of tooth positions, shape of pars facialis) cannot be recognized (see also Text-fig. 3 , bottom picture). It seems that the maxilla adjoins the posterolateral end of the premaxilla from the outer side. The frontoparietal projects anteriorly as a slender median process, originally inserted between the two nasals. This means that both nasals (neither of them is preserved) were in contact with one another only over a short section anteriorly, whereas their medial margins were divergent posteriorly. Similar, though not so prominent processes project anterolaterally on both sides of the anterior margin of the frontoparietal. Parasagittal ridges (prominent arch-like crests on the dorsal surface of the bone, with a deep antero-posterior depression between them) run posteriorly from each anterolateral process, approaching each other at the interorbital portion of the bone, but diverging again in its parietal portion, and terminating on the paraoccipital processes. The posterior margin of the frontoparietal is widely convex; the paraoccipital processes do not extend beyond the most posterior part of this convexity, which is thus the most posterior part of the bone. Underneath the imprint of the anterior part of the frontoparietal, there is an imprint of the sphenethmoid, which is well delimited posteriorly; the posterior margin of the sphenethmoid extends to the middle of the antero-posterior diameter of the orbit. The ramus maxillaris of the pterygoid is markedly sigmoid in shape, the end of the ramus interior (= medialis) is rounded, and the margin between the ramus interior and ramus posterior is concave. It seems that the coronoid process of the angular is inclined medially.

Altogether nine vertebrae can be recognized. All are short and broad, hence the presacral vertebral column is comparatively short. The neural arches are imbricate and bear a median crest on their dorsal surface, not extending onto adjacent posterior vertebra. V1 and V2 are fused, V2 bears a pair of transverse processes which are thick proximally and slightly inclined posteriorly (see, however, Text-fig. 3 , bottom picture). Transverse processes of V3 and V4 are the longest, and markedly inclined posteriorly (those of V3 are cranked posteriorly in the middle of their length, those of V4 are straight). Transverse processes of V5 are also inclined posteriorly, but moderately bent anteriorly, and those of V6 are straight, perpendicular to the body axis, and directed to the ends of the processes of V5. Transverse processes of V7 are rudimentary and, as Goldfuss (1831) already noted, they lean against the anterior margin of the sacral wings, but it cannot be decided with certainty if they are fused with the sacral wings. V8 and V9, including their transverse processes, are fused with each other, however, proximal parts of the processes remain separated, so there are openings between them. The lateral margin of the sacral wings is slightly concave. The urostyle is stout and comparatively short. There is no evidence that there was a postsacral vertebra on the urostyle with a pair of short transverse processes as Goldfuss (1831) believed.

The anterior and lateral margins of the scapula meet at a right angle, the anterior margin could probably be straight or even moderately convex. The posterior margin of the scapula is distinctly concave. The suprascapula (preserved as a faint imprint on the right side of the specimen) has a distal margin only moderately concave and nearly symmetrical (not extending in two processes of different size). The humerus seems to have a prominent ventral crista in its anterior third, and the distal end of the radioulna seems to be broad. The only preserved elements of the carpus are the ulnare, radiale, and the centrale 2. Other carpal elements were probably still cartilaginous, although the holotype specimen was obviously adult (judging by the ossified epiphyses of the femur and tibiofibula). The phalangeal formula is 2-2-3-3, and all fingers were of approximately the same length (see the right fore limb).

The ilia are disarticulated from one another and twisted along the axis of their shaft, so they display their lateral side with a large acetabulum. The iliac shaft was regularly bent along the whole of its length. The ischia were disarticulated from the ilia, but coalesced with one another. The femur is slightly sigmoid in shape. The tibiale and fibulare are not fused with one another. The phalangeal formula cannot be reconstructed, but the prehallux is preserved.

Measurements: Snout-vent length (SVL, measured from the anterior end of the suture between the two premaxillae to the tip of the urostyle) 53.2 mm; humerus (H) 17.0 mm; metacarpal 2 (Mc2) 11.0 mm; femur (F) 26.0 mm; tibiofibula (TF) 22.7 mm; fibulare (Fb) 11.2 mm. Ratios: SVL:H 3.13; SVL:H+Mc 2 1.9; F:TF 1.15; SVL:F+TF+Tb 0.89.

Figures

Text-fig. 1 Palaeobatrachus diluvianus (GOLDFUSS, 1831). Holotype (STIPB-Goldfuss-1343) deposited in Goldfuss Museum, Steinmann- Institut für Geologie, Mineralogie und Paläontologie, Rheinische Friedrich-Wilhelms Universität, Bonn, Germany. Photograph courtesy Steinmann-Institut.

Text-fig. 5 Locality Orsberg near Erpel, Germany. Type locality of Palaeobatrachus diluvianus (GOLDFUSS, 1831). Abandoned open-cast mine, with traces of mining activities. Situation as on June 23rd 2014.

Text-fig. 3 Reconstruction of Palaeobatrachus diluvianus (“Palaeobatrachus Goldfussi”) holotype by Meyer (1860: pl. 18, figs 1, 2). Small bone close to right hindlimb and other details are clear evidences that this specimen and the specimen in Text-fig. 1 are the same. The drawing above was made from the original imprint in sediment (although the skull is drawn as if it were a real skeleton in dorsal view), but the drawing below depicts the cast made of bread, i.e., real anatomical situation (note that both drawings are mirror-reversed).