Osteological Atlas of Melanophryniscus (Anura, Bufonidae): a Synthesis after 150 years of Skeletal Studies in the Genus Herpetological Monographs

DEFOREL, FACUNDO; DUPORT BRU, ANA SOFÍA; ROSSET, SERGIO; BALDO, DIEGO (CO-LAST AND CORRESPONDING AUTHOR); VERA CANDIOTI, MARÍA FLORENCIA (CO-LAST AND CORRESPONDING AUTHOR)

HERPETOLOGICAL MONOGRAPHS

HERPETOLOGISTS LEAGUE

Lugar: Lawrence; Año: 2021 vol. 35 p. 1 - 27

0733-1347

Toads of the genus Melanophryniscus are known since the last middle of the XIXcentury, and the first skeletal description was made early in 1875. However, it was notuntil the 1970s that osteological variation was discussed in a more inclusive taxonomicscenario. Derived from this, the first morphological synapomorphies proposed for thegenus represented skeletal traits extracted from the few species considered in thatstudies. In this work, we examined the skeletons of 25 nominal species ofMelanophryniscus plus three species under description, in order to register theosteological variation and discuss the validity of those synapomorphic charactersproposed, not only by analyzing their distribution within the genus but also bycomparing them with the skeletal data available in the bibliography for other basalbufonids. Our results show that main variations within the genus are related to changesin absolute body size and some proportions of postcranial elements. Except for M.setiba , a basal species that exhibits a number of autapomorphies, most skeletal traitsare quite conserved throughout the genus. Members of the M. tumifrons group aredistinctive by their nasal region, which tends to be higher than in other species, domeshaped,and strongly exostosed. Most features considered diagnostic of the genusoccur in other basal bufonids, and are highly polymorphic, and this challenges earlierdiscussions on putative synapomorphies. For instance, exostosed frontoparietals onlyoccur in M. setiba and M. klappenbachi , and the condition was also recorded forOsornophryne . The frontoparietal fontanelle, if present, may show different shapesand sizes (often similar to those in Osornophryne and some species of Atelopus ).The zygomatic ramus of the squamosal may be absent or present as a small process,as registered for some species of Atelopus , Osornophryne , and Truebella .Finally, posterolateral processes of the hyoid were observed in some basal speciesand hence we propose an alternative interpretation on its presence and distribution inthe genus.