Pelodytes BONAPARTE , 1838

Rage, Jean-Claude, 2016, Frogs (Amphibia, Anura) From The Eocene And Oligocene Of The Phosphorites Du Quercy (France). An Overview, Fossil Imprint 72 (1 - 2), pp. 53-66 : 56-57

cf. Pelodytes BONAPARTE, 1838

( Text-fig. 3 )

In the Phosphorites, the taxon is represented by vertebrae, ilia, humeri and one fused tibiale-fibulare ( Text-fig. 3 ). Vertebrae show a combination of features that is characteristic of Pelodytes ( Text-fig. 3 : 1, 2). They are proceolous, lightly built and the centrum, cotyle and condyle all are markedly depressed dorsoventrally. In ventral aspect, the ventral parts of the lateral walls typically extend laterally on either side of the centrum. The neural arch is of the imbricate type, i.e. it is anteroposteriorly long. The posterior projection of the neural spine is relatively weak. In posterior presacral vertebrae, the bases of the transverse processes originate approximately below the prezygapophyses and they project markedly anterolaterally. One incomplete sacral vertebra may belong to this taxon; however, it is regarded as belonging to an indeterminate anuran because it bears postzygapophyses (see below: ‘Problematic taxa’).

The ilia lack both a dorsal crest and a tuber superius, as do those of pelobatids ( Text-fig. 3 : 4). However, their shaft is markedly curved in lateral view and the dorsal border of their pars ascendens (ischiatic process) is slightly curved dorsally, which distinguishes them from pelobatid ilia.

Humeri are very similar to those of Pelodytes ( Text-fig. 3 : 3). They have a slender and almost straight diaphysis that bears ventral and paraventral crests. The articular ball is well defined, comparatively small and scarcely shifted laterally. The distal part of the lateral border of the bone (crista lateralis not taken into account), close to the articular ball, forms a gentle curve that is slightly convex laterally; this part of the humerus is generally concave in anurans.

A fused tibiale-fibulare ( Text-fig. 3 : 5) belonging to a pelodytid was recovered among the specimens of anurans from the late Eocene of Malpérié (MP 17) by Duffaud (2000). In almost all anurans, the tibiale and fibulare are elongate and fused only at their extremities. However, in pelodytids, centrolenids (an extant Central and South American family) and Tephrodytes HENRICI, 1994 (but not in rhinophrynids, contra Trueb 1973), they are fused throughout their length and form a single element. This element thus resembles the anuran tibiofibula; however, it is shorter and its extremities are more expanded. In addition the proximal ends of the tibiale and fibulare are approximately circular, whereas the distal extremities are clearly flattened. Traces of the fusion remain as grooves, except in the central portion of the bone. This tibiale-fibulare from Malpérié clearly displays this morphology, which is characteristic of Pelodytes ( Sanchiz 1978) . It differs from that of Miopelodytes TAYLOR, 1941 in being more slender; more specifically, its extremities are less expanded. The fused tibiale-fibulare of centrolenids is markedly more elongate and slender ( Guayasamin et al. 2009). The fused tibiale-fibulare from Malpérié cannot be distinguished from the tibiale-fibulare of extant Pelodytes and it also closely resembles that of Tephrodytes (Oligocene-Miocene transition of the USA; Henrici 1994). Tephrodytes was first referred to the Pelodytidae ( Henrici 1994) but Henrici et al. (2013) placed it among pelobatids s.l. However, the morphology of various bones suggests that Tephrodytes may be more closely related to the Pelodytidae .

In conclusion, the specimens from the Phosphorites allocated to Pelodytidae are quite similar to those of extant Pelodytes . Henrici et al. (2013: 304) noted that reliable referral of the remains from the Eocene of Europe to pelodytids (as cf. Pelodytes ) would require finding of a fused tibiale-fibulare in the same localities. The recovery of such a tibiale-fibulare confirms that a fossil taxon closely related to Pelodytes , if not Pelodytes , is present in the late middle and late Eocene (from MP 16 to MP 19) of western Europe, more specifically in the Phosphorites.

Figures

Text-fig. 3. Pelodytidae (cf. Pelodytes) from the Phosphorites du Quercy. 1: presacral vertebra UM-MAL 617, from the late Eocene of Malpérié (MP 17), in dorsal (a), anterior (b), and ventral (c) views. 2: posterior presacral vertebra UM-SNB 2406, from the late Eocene of Sainte-Néboule (MP 18), in anterior (a) and ventral (b) views. 3: right humerus UM-ECA 2556, from the late Eocene of Escamps (MP 19), in ventral view. 4: left ilium UM-ECA 2534, from the late Eocene of Escamps (MP 19), in lateral view. 5: right tibiale-fibulare UM-MAL 616, from the late Eocene (MP 17) of Malpérié (proximal section (a); dorsal view (b); and distal section (c)). Each scale bar = 3 mm.