Palaeobatrachus robustus Hossini & Rage, 2000

Vasilyan, Davit, Cernansky, Andrej, Szyndlar, Zbigniew & Moers, Thomas, 2022, Amphibian and reptilian fauna from the early Miocene of Echzell, Germany, Fossil Record 25 (1), pp. 99-145 : 99

Palaeobatrachus robustus Hossini & Rage, 2000

Fig. 9I-W

Material.

Four frontoparietals HLMD-Ez 2076-2078, five ilia HLMD-Ez 2079-2081, two angulars HLMD-Ez 2082, 2083, five jaw bones HLMD-Ez 2084, 2085.

Description.

Frontoparietals are flat and thin. They represent small-sized individuals. The parasagittal ridges are well-developed and build the limit between the flat dorsal surface of the bones and somewhat concave orbital margins. The parasagittal ridges are very closely located near the midpoint of the bone and form a sandglass shape at the dorsal surface of the bone. The dorsal surface of the bone between the parasagittal ridges is irregular and pierced by small foramina (pineal foramen sensu Villa et al. 2016) and pits (Fig. 9L ). Posteriorly, the surface of the frontoparietal table is flat and rather smooth. The irregularities, if present, are weakly pronounced. The parasagittal ridges reach the paroccipital processes posteriorly (Fig. 9I, K ). The latter are not fully preserved. Only their bases are observable, which in turn, possess a crest. A smaller posterior median crest is present along the anteroposterior axis of the bone which starts from the posterior margin of the frontoparietal table. The posterior margin of the bone between the median margin and paroccipital process is arched and forms a “bilobed” outline (Fig. 9K ). The median crest is lower than the paroccipital processes. Judging from the preserved portions of the paroccipital process and posterior median process, a shorter length of the former in comparison to the latter can be assumed. In ventral view, the frontoparietal incrassation, visible only in HLMD-Ez 2077 (Fig. 9J ), representing the posterior portion of the bone, has a round outline with slightly prominent margins. No structure similar to the lanceolate area (sensu Roček et al. 2015) is observable on the available frontoparietals.

Premaxillae, maxillae, vomer: all three bones are fragmentarily preserved and do not allow any detailed description. The preserved teeth and tooth pedicles display diagnostic characters, such as the conical and slightly lingually bent ankylosed teeth. At the tooth basis, large and deep pits are preserved. The bicuspid tooth has a small labial and large apical cusps (Fig. 9N, O , HLMD-Ez 2084).

Angulars: in total, two angulars can be clearly assigned to this taxon. They are elongated and curved bones. The coronoid process is compact and can be oval to drop-shape (Fig. 9P, Q ). Its surface is concave, rather smooth and can possess tubercles (muscle scars). The Meckelian groove behind the coronoid process is broad and opens dorsally, whereas anteriorly, it is open laterally or slightly dorsolaterally.

Ilium: The acetabular region of the ilium is robust. The dorsal prominence (sensu Gómez and Turazzini 2015) is not well-developed. The drop-shape dorsal protuberance (sensu Gómez and Turazzinin 2015) is large (Fig. 9R ) and can be weakly to moderately developed (Fig. 9V ). Its surface is rather smooth, and its small posterior portion is located above the anterior margin of the acetabular crest. The ventral acetabular expansion (also known as pars descendens) does not project ventrally, but it is massive in ventral/dorsal views (Fig. 9R ). The dorsal acetabular expansion (also known as pars ascendens), even if only fragmentarily preserved, is moderately developed. The ventral half of the acetabular fossa is massive. The well-developed ventral portion of the acetabular crest projects laterally and contributes to the ventroanterior surface of the acetabular region of the ilia. In larger individuals (e.g. HLMD-Ez 2080), an oval knob-like flat surface is present in the lateroventral cornet between the iliac shaft and acetabulum (Fig. 9V ). It represents most probably the attachment surface for the muscle iliacus internus (sensu Gómez and Turazzini 2015). In posterior view, the well-pronounced interiliac groove and laterally projecting acetabular crest are observable. The iliac shaft is moderately developed, lateromedially flattened and has a rather smooth surface.

Remarks.

The fossil remains display characteristic features of the genus Palaeobatrachus as well as the family Palaeobatrachidae such as: 1) azygous frontoparietal with a flat dorsal surface; 2) angular coronoid process smooth and/or covered by muscle scars; 3) anteroventrally extending large acetabulum; 4) acetabular area strongly protruding; 5) well-pronounced interiliac groove ( Wuttke et al. 2012) and 6) paroccipital processes do not extend probably beyond the level of posterior median process ( Roček et al. 2015; see characters 12, table 2). Among the material available bones, only the frontoparietal can be used for the species-level identification since other elements such as ilium, angular do not contain sufficient diagnostic characters. The Palaeobatrachus frontoparietal from Echzell can be distinguished from other Miocene forms, e.g. P. hiri (locs. Bátraszölos and Sámsonhaza, Venczel 2004), and P. sp. A (loc. Rudabanya, Roček 2005) by the sculptured frontoparietal (vs. unsculptured in P. hiri and P. sp. A) and weakly developed frontoparietal incrassation (vs. strongly developed, in form of crests in P. hiri and P. sp. A). The Echzell frontoparietals strongly resemble the morphology of the P. robustus from the early Miocene (MN2) of France (loc. Laugnac, Hossini and Rage 2000), in having 1) a comparable sculpture on dorsal surface of the bone; 2) the skull table narrows in the midpoint of the bone, giving a sandglass shape; 3) weakly developed, rounded frontoparietal incrassation. We did not compare with P. hauffianus from Randecker Maar, Germany (middle Miocene) ( Roček et al. 2006) which taxonomic status still needs revision.

Figures

Figure 9. Frogs from Echzell locality. Ilia of Pelophylax sp. HLMD-Ez 2089 (A, B) and HLMD-Ez 2090 (C, D). Ilia of Rana sp. HLMD-Ez 2093 (E, F) and HLMD-Ez 2094 (G, H). Palaeobatrachus robustus (I-W). Frontoparietals HLMD-Ez 2077 (I, J), HLMD-Ez 2078 (K) and HLMD-Ez 2076 (L, M). Jaw bone HLMD-Ez 2084 (N, O). Angulars HLMD-Ez 2083 (P) and HLMD-Ez 2082 (Q). Ilia HLMD-Ez 2079 (R-T) and HLMD-Ez 2080 (V, W). Bones are figured in (A, D, E, G, M, R, V) lateral, (B, C, F, H, S) posterior, (I, K, L, P, Q) dorsal, (J, O) ventral, (N) labial and (T, W) medial views. Scale bars: 1 mm.