Aparasphenodon Miranda-Ribeiro, 1920 or Corythomantis Boulenger, 1896? An osteological case of study.

Some frogs from Hylidae family, tibe Lophiohylini, are known as “casque-headed frogs”, characterized by their well developed hyper ossified skull and phragmotic behavior, the act of use some part of the body - in this case, the head - to close a burrow. Recently, a new species of casque-headed frog, Aparasphenodon pomba, was described, however, no osteological analyzes were performed, which could clarify its generic position. In this work, we describe the skull of A. pomba using the diaphonization technique, and some questions arose. The cranial osteology shows the skull longer than wide, premaxillaries almost straight; prenasal bone absent; vomers widely separated with each other, with dentigerous process curve in a transverse plane, bearing 7 to 10 theeth; neopalatine robust, bearing a series of odontoids along the ventral crest; nasal large, long and extends anteriorly to cover the alary process of the premaxilla; maxillary moderately robust, presents small bone spicules in all its extension; frontoparietals converge medially throughout their lengths; dermal sphenethmoid triangular shaped; squamosal arched in dorsal view; pterygoid well developed. The specimens of A. pomba hasn’t the prenasal bone, considered as the unique putative morphological synapomorphy of the genus Aparasphenodon, differing it from the other species. In addition, they present a single, median, subgular vocal sac. Furthermore, the morphology of this species’s cranium looks more like with Corythomantis than Aparasphenodon, such as the triangular-shaped dermal sphenethmoid (losangular-shaped in Aparasphenodon), otic ramus of the squamosal partially covered by the posterolateral corner of frontoparietal (not covered in Aparasphenodon); The patterns of network spicules are also very similar to the Corythomantis genus pattern, and mainly the nasals that conceal the alary process of premaxillaries, considered as the only putative synapomorphy for this genus. Because of these morphological similarities, we support that A. pomba may belong to the Corythomantis genus.