The Late Cretaceous Neobatrachian frog Baurubatrachus Revisited

BÁEZ, ANA MARÍA; MUZZOPAPPA, PAULA; NICOLI, LAURA

Rio de Janeiro, Rio de Janeiro

Congreso; II Congresso Latino-Americano de Paleontologia de Vertebrados; 2005

Museu Nacional

The rather complete and partially articulated skeleton of Baurubatrachus pricei was briefly described by Báez and Peri in 1989. The material was collected by Llewellyn Ivor Price in the Serra da Galga Member of the Marilia Formation of the Bauru Basin near Peirópolis, Minas Gerais State. The bearing bed consists of coarse-grained sandstone, the depositional environment of which was interpreted as a braided fluvial system of Maastrichtian age. We herein redescribe this taxon based upon further preparation of the single known specimen and discuss its relationships, although the lack of a robust hypothesis of relationships of neobatrachian taxa, based on morphological data, makes it difficult to evaluate its phylogenetic position. Some of the more bizarre features of Baurubatrachus lie in the hyperossified and exostosed skull. Exocranial bones are deeply incised by pits and many are fused to one another and to the underlying endocranial elements, thereby obscuring bone boundaries. The orbits are surrounded by frontoparietals, nasals, and squamosals; maxillae are excluded from, or participate minimally in, the formation of the orbital margins. The squamosals articulate extensively with the maxillae and constitute the major roofing elements of the temporal region, which is closed unlike the great fenestration of this region in most frogs. A unique feature is the presence of a small, dorso-laterally placed, circular fenestra (which seems to include a small remnant of the subtemporal fenestra) on each side of the skull. This configuration might be related to a peculiar mode of sound reception. The bones bordering these fenestrae (squamosals, quadratojugals, maxillae?) form thickened rims around these openings, which bear scars that suggest the attachment of the tympanic membranes or plates; however, the stapes are not preserved. Coossification of the tympanic annuli might also have occurred. It is interpreted that many cranial features of Baurubatrachus, such as the squamosal-maxilla contact, in addition to the pterygoid, quadratojugal-squamosal contact, contribute to stabilize the maxilary arcade. This, together with the strong jaw and teeth, might be related to feeding on large prey. Some of these features appear convergently in several neobatrachian groups, including the strictly South American ceratophrynes to which Baurubatrachus bears an overall resemblance. This extinct taxon shares with ceratophrynes the widely expanded transverse processes of presacrals III and IV that are longer than the sacral diapophyses, and high neural spines (those of the presacrals I and II distally fused) on all presacrals. However, many features of Baurubatrachus differ from the conditions present in all living ceratophryne taxa and, presumably, in their most recent common ancestor. Some of these features are relatively lower skull, pedicellate teeth, maxillary pars palatina perpendicular to the pars facialis, scapula bearing a crest (tenuitas cristaeformis) along its anterior edge, long ilial shaft bearing a dorsal crest, and tibiofibula longer than femur. Although Baurubatrachus lived in arid or semiarid conditions, not unlike those that prevail in the regions where some of the ceratophrynes live today, significant differences in body proportions might be suggestive of a different lifestyle and / or different habits.