new crocodylian from the Palaeocene of Patagonia with implications for the early palaeobiogeographic history of the Caimaninae

BONA, P.; EZCURRA, M. D.; BARRIOS, F.; FERNANDEZ BLACO, M. V.

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2017

Caimaninae is a crocodylian clade currently restricted to South and Central America. The oldest members of the group are from lower Palaeocene (Danian) localities of the Salamanca Formation (Chubut Province, Argentina). We report here a new caimanine from these same levels (MLP 80-X-10-1) represented by a skull table and a partial braincase. Its phylogenetic relationships were explored using standard characters and a morphogeometric bidimensional configuration of the skull table in a cladistic analysis using TNT 1.5. The phylogenetic results were used to conduct a quantitative palaeobiogeographic analysis using the event-based supermodel analysis implemented in the package BioGeoBEARS in R. The new taxon is recovered as the most basal member of the South American Caimaninae, while the Cretaceous North American lineage of ?Brachychampsa and related forms? is positioned as the most basal Caimaninae. The biogeographic results found DEC+j, as it is the model that best fit our data, depict that north-central North America was the ancestral area of Caimaninae, showing that the group was more widespread than thought and became regionally extinct in North America during the latest Cretaceous. A dispersal event from north-central North America to South America during the middle Late Cretaceous (85−90 Mya) explains the arrival of the group to the southern part of the continent. Our results also indicate that the Palaeogene assemblage of Patagonian crocodylians is composed of three lineages of caimanines, as a consequence of independent and non-coetaneous dispersal events that occurred between North and South America and within South America around the Cretaceous-Palaeogene boundary.