A new Palaeocene crocodylian from southern Argentina sheds light on the early history of caimanines

BONA, PAULA; EZCURRA, MARTÍN D.; BARRIOS, FRANCISCO; FERNANDEZ BLANCO, MARÍA V.

PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON. SERIES B: BIOLOGICAL SCIENCES.

ROYAL SOC

Lugar: Londres; Año: 2018 vol. 285

0962-8452

Caimanines are crocodylians currently restricted to South and CentralAmerica and the oldest members are from lower Palaeocene localities of theSalamanca Formation (Chubut Province, Argentina). We report here a newcaimanine from this same unit represented by a skull roof and partialbraincase. Its phylogenetic relationships were explored in a cladisticanalysis using standard characters and a morphogeometric two-dimensionalconfiguration of the skull roof. The phylogenetic results were used for anevent-based supermodel quantitative palaeobiogeographic analysis. Thenew species is recovered as the most basal member of the South Americancaimanines, and the Cretaceous North American lineage ?Brachychampsa andrelated forms? as the most basal Caimaninae. The biogeographic resultsestimated north-central North America as the ancestral area of Caimaninae,showing that the Cretaceous and Palaeocene species of the group were morewidespread than thought and became regionally extinct in North Americaaround the Cretaceous?Palaeocene boundary. A dispersal event from northcentralNorth America during the middle Late Cretaceous explains the arrivalof the group to South America. The Palaeogene assemblage of Patagonian crocodyliansis composed of three lineages of caimanines as a consequence ofindependent dispersal events that occurred between North and SouthAmericaand within South America around the Cretaceous?Palaeogene boundary.