New anuran remains from the late Cretaceous of western São Paulo (Brazil) enlarge the record of the bizarre frog Baurubatrachus

Abstract

We present new remains of a fossil frog from the outcrops of the Adamantina Formation (Campanian; Bauru Group) at Catanduva city, São Paulo state, Brazil. The specimen consists of associated, though disarticulated, cranial and postcranial elements, whose preservation retains many details; some of the bones are even preserved in their full extent. Dermal skullroof elements show hyperossification in the ways of sculpturing and wide extension of some bones. According to its ossification degree, including the fused ilia and the fully ossified puboischiadic plate, the skeleton corresponds to a fully grown individual. The preliminary study indicates this specimen has the peculiar combination of characters described for the neobatrachian Baurubatrachus pricei from the younger Serra da Galga Formation (Maastrichtian) of the same group. This combination includes a squamosal bearing a lamella alaris surrounding what might have been the tympanic membrane, a long scapula having a ventrally deflected tenuita cristaeformis, and ischia well ossified with an extensive posterodorsal expansion. The specimen is certainly referred to Baurubatrachus, denoting the early presence of this taxon in the Campanian Adamantina Formation. The new specimen shows some differences from the holotype of B. pricei regarding the proportion of the skeleton, suggesting that it might represent a new species. It is noteworthy, however, the striking similarity of the two specimens even coming from different and successive formations, indicating a marked morphological stasis for the genus. Besides, the Bauru Group stands as a relevant unit for the understanding of the early evolution of Neobatrachia.