New records of pipid frogs from the Late Cretaceous Allen Formation of Patagonia and modular evolution of xenopodinomorphs

GÓMEZ, R.O.; BÁEZ, A.M.

Buenos Aires

Congreso; XXVI Jornadas Argentinas de Paleontología de Vertebrados; 2012

Universidad Maimónides-CEBBAD-Fundación de Historia Natural Félix de Azara

Pipids are fully aquatic frogs that today inhabit freshwater environments of northern South America (Pipini) and sub-Saharan Africa (Xenopodinae and Hymenochirini), with a fossil record dating back to the mid-Cretaceous. Known records of this lineage in the Allen Formation (Campanian?Maastrichtian) of Patagonia consist of incomplete sphenethmoids of uncertain affinities. Recent finds in exposures of this unit in the Trapalcó and Santa Rosa depressions, Río Negro Province, provide new data to elucidate their systematic relationships. The new material (Museo Municipal de Lamarque, MML-PV 1042, 1047, 1057?1064) includes otic capsules, a sphenethmoid, ilia, humeri, and vertebrae. A cladistic analysis including osteological, as well as molecular, data places the pipid from Allen as a non-xenopodine xenopodinomorph, together with other fossil pipids from South America and some Cretaceous taxa from Africa. These fossil species exhibit the plesiomorphic condition of several xenopodine synapomorphies, including the sphenethmoid surrounding anteriorly the frontoparietal fenestra, olfactory and orbitonasal foramina completely enclosed in bone, flat zygapophyseal facets, and, also, several ilial traits. Notably, the morphology of the pipid capsules from Allen is remarkably similar to that of extant xenopodines. The conserved condition of this cranial structure contrasts with the many changes that have occured in other parts of the skeleton, including other parts of the neurocranium, in this lineage. This anatomically disjunctive pattern of change points to a modular evolution of xenopodinomorphs during the last 70 million years.