A review of Neusibatrachus wilferti, an Early Cretaceous frog from the Montsec Range, Northeastern Spain

Neusibatrachus wilferti is an anuran from the late Berriasian–early Valanginian fossiliferous lacustrine limestones that are exposed in the eastern part of the Montsec Range, province of Lleida, Spain. It was originally described by Seiffert in 1972 and its phylogenetic position has since been discussed. Neusibatrachus has been considered an undeterminable fossil, an abnormal individual, or a primitive palaeobatrachid. Here we redescribe the only available specimen, and clarify features, such as absence of palatines, nine presacrals, and procoelous vertebral centra, that have been the subject of previous debates. We consider the specimen to be a postmetamorphic individual and make developmental interpretations of some of its characters. In particular, we provide evidence of a living anuran (Rana iberica) that resembles Neusibatrachus in the development of intervertebral articulations. Neusibatrachus is considered a valid genus, which differs from other anurans, except for the pipoids, in the joint presence of an azygous frontoparietal and a parasphenoid lacking the subotic alae, although it differs from the pipoids in having nine presacral vertebrae. Morphological evidence indicates that Neusibatrachus is related to Xenoanura, the pipoid branch in the living Amphibia Tree of Life based on molecular data. Moreover, it might be a member of the pipoid clade proper, which presently includes the Pipidae, Rhinophrynidae, and several fossil taxa, including the Palaeobatrachidae, although the evidence is not conclusive