Palaeobatrachus eurydices

Description. IPB-HaR 2429 (Figure 16 A-C) is a fragment of maxilla, measuring about 5.5 mm in length and preserving only the area of the processus palatinus. The bone is robustly built. On the medial side, part of the tooth row is preserved, even though in bad conditions. Four wide tooth positions are preserved, one of them still hosting the base of a tooth. The tooth positions are separated by knob-like structures. The lamina horizontalis is mostly broken, but it clearly extended medially with a toothless portion. No clear ridge is visible ventrally separating the toothed and toothless portion of the lamina. On its dorsal side, a deep recessus vaginiformis is present. The processus palatinus is represented in this specimen by a low, subtriangular structure with a truncated dorsal tip. In dorsal view, it is shifted medially, thus originating a concavity on the lateral surface of the maxilla. Both the anterior and posterior margins of the process are distinctly irregular, and its lateral surface displays few foramina. IPB-HaR 2021 (Figure 16 D-G) is a fragmentary sphenethmoid. It is anteroposteriorly elongated and large-sized. The lateral margins of the bone are rather eroded, but distinctly developed laminae supraorbitalis and trabecula seem not to be present. In dorsal view, a long and U-shaped fenestra frontoparietalis is recognizable, even if the left portion of the bone is lacking. Anteriorly to the fenestra, the dorsal surface of the bone is smooth. The contact surface with the parasphenoid is visible on the ventral surface: it is delimited laterally by two low ridges and widens anteriorly. Angulars are robust and large-sized. They have a rather deep sulcus cartilagine Meckeli and an anteroposteriorly elongate, stocky and dorsoventrally compressed processus coronoideus. The dorsal surface of the latter is strongly irregular, with pits and / or ridges, and shows a certain degree of individual variation (Figure 17). A few angulars, such as e. g., IPB-HaR 2111 (Figure 17 A) and IPB-HaR 2418, bear a small tubercle on the lateral side, in correspondence with the anterior end of the processus coronoideus. The extremitas spatulata is short and broad. IPB-HaR 2030 is a fragmentary trunk vertebra provided with a very dorsoventrally compressed centrum. The latter is procoelous, wide, and shows numerous small pits on the ventral surface. Humeri (Figure 16 H-M) are very large-sized and lack a fossa cubitalis ventralis. The eminentia capitata and the epicondyles are distally eroded and were probably partly cartilaginous in the living animal. The epicondylus ulnaris is only slightly larger than the epicondylus radialis. The olecranon scar is depressed, but the articular surface with the olecranon of the radioulna is small and poorly developed. All specimens but IPB-HaR 2420 preserve only the distal epiphysis and the distal part of the diaphysis. IPB-HaR 2420 is more preserved, but the proximal end of the bone is still missing. A hint of a robust crista ventralis is recognizable on the ventral surface of the humeri. This is particularly evident in IPB-HaR 2420, which also express the base of a crista paraventralis. Cristae medialis and lateralis are not developed. Ilia (Figure 16 N-Q) show a well-developed and elongated dorsal tubercle, but no dorsal crest. The tubercle bends in lateral direction. The large acetabular fossa has a prominent anteroventral rim. The ventral acetabular expansion is not developed, whereas the dorsal one is moderately developed. A supraacetabular fossa is visible dorsally to the acetabulum. A wide and deep interiliac groove is visible on the medial surface of the body of the bone.

Figures 16 – 17

Remarks. Clear diagnostic features of palaeobatrachid anurans in the above-described material are the following (Wuttke et al., 2012; Roček, 2013; Roček et al., 2021): knob-like structures separating tooth positions in the maxilla; elongated sphenethmoid, provided with frontoparietal fenestra longer than half the total length of the bone and with two parallel ridges delimiting the articulation area for the parasphenoid on the ventral surface; coronoid process of the angular either smooth or bearing muscle scars on dorsal surface; vertebral centrum strongly dorsoventrally compressed and with numerous pits on the ventral surface; humerus devoid of fossa cubitalis ventralis (different from Eocene palaeobatrachids, though) and provided with a comparatively small eminentia capitata that is located on or near the long axis of bone, as well as similar-sized epicondyles; ilium with massive dorsal acetabular expansion; large acetabular fossa extending anteroventrally beyond the margin of the ilial body, thus concealing the ventral expansion; dorsal tubercle protruding only slightly in dorsal direction, but more prominent laterally and bearing muscle scars on the lateral surface; distinct horizontal depression on the inner surface of the iliac shaft. Specific attribution to P. eurydices appears also justified, due to the following combination of features (Villa et al., 2016): the interorbital section of the processus cultriformis of the parasphenoid was narrow, but the process becomes wider towards the anterior (as suggested by the divergent longitudinal ridges on the ventral side of sphenethmoid, which delimit laterally the area of attachment of the parasphenoid); the sphenethmoid lacks articular facets for the nasals; the dorsal surface of the sphenethmoid shows no median ridge; the processus coronoideus of the angular extends parallel to most of the extremitas spatulata; the extremitas spatulata is short and broad; the fossa cubitalis ventralis of humerus is absent. Despite its very fragmentary status, the maxilla IPB-HaR 2429 is also very similar in morphology to maxillae of P. eurydices. In particular, it could be somehow representative of a sort of “ intermediate ” stage between the supposed juvenile maxilla reported by Villa et al. (2016) and the adult ones. Similar to the purported juvenile specimen, IPB-HaR 2429 has a subtriangular processus palatinus, which gives to the bone a concave lateral appearance in dorsal view due to a slight medial shifting. However, the size of the specimen, as well as the number of teeth in the processus palatinus area and the absence of a ridge separating the toothed and toothless portions of the ventral surface of the lamina horizontalis, seem to be more comparable with the adult holotype maxilla of P. eurydices.

Material. Hambach 11: one sphenethmoid (IPB-HaR 2021); 11 angulars (IPB-HaR 2110 / 2113, IPB-HaR 2129 / 2132, IPB-HaR 2144 / 2146); one trunk vertebra (IPB-HaR 2030); five humeri (IPB-HaR 2148 / 2152); five ilia (IPB-HaR 2099 / 2102, IPB-HaR 2147). Hambach 11 C: one maxilla (IPB-HaR 2429); one angular (IPB-HaR 2418); two humeri (IPB-HaR 2419 / 2420).