Postcranial Osteogenesis of the Helmeted Water Toad Calyptocephalella gayi (Neobatrachia: Calyptocephalellidae) with Comments on the Osteology of Australobatrachians

MUZZOPAPPA, PAULA; PUGENER, L. ANALÍA; BÁEZ, ANA MARÍA

JOURNAL OF MORPHOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Año: 2016 vol. 277 p. 204 - 230

0362-2525

Calyptocephalella gayi is one of over six thousand neobatrachians (the so?called advanced frogs) arranged into two main groups, Hyloides and Ranoides. Phylogenetically, C. gayi is placed in Australobatrachia, a Gondwanan clade that is either the most basal clade of Hyloides or the sister group of Hyloidea, depending on the cladistic hypothesis; as such, this species is a key taxon in the study of the early evolution of Neobatrachia. The ontogeny of the postcranial skeleton of C. gayi is described in the present paper. Because the description is based on chondrification and ossification of cartilages and bones, a growth series of tadpoles, juveniles, and adult individuals was examined. Particular attention was devoted to some developmental aspects and morphological traits of the adult skeleton. The body of Presacral Vertebra VIII is formed from three centers of ossification, instead of the usual two dorsolateral centers observed in the remaining vertebrae of C. gayi, as well as in most anuran taxa for which the development of the axial skeleton is known. Each half of the pelvic girdle arises from a single cartilaginous element. The early development of the autopodia of both the fore- and hind limbs includes the presence of an additional chondral element, which occurs during the formation of Distal Carpal 5 and the transient formation of Distal Tarsal 4 before the latter is incorporated in the cartilaginous distal end of the fibular. Some osteological aspects of other australobatrachian anurans also are reviewed (e.g., presence of intervertebral discs) based on reports in the literature, as well as first hand observations. In the course of this study, it became evident that further osteological studies are needed to formulate a clear picture of the evolution of skeletal characters not only within Australobatrachia, but also within Neobatrachia.