ARE EXTANT PODOCNEMIDID TURTLES RELICTS OF A WIDESPREAD CRETACEOUS ANCESTOR?

Abstract

We re-analyzed the most recent morphological data matrix for Pleurodira with inclusion of the Upper Cretaceous Brazilian pleurodiran turtle, Bauruemys elegans (Suárez, 1969), as new Operational Taxonomic Unit. An exhaustive search based on 50 characters for 11 taxa was performed to asses the phylogenetic relationships within the Pelomedusoides and a single most parsimonious tree of 64 steps was found. This new phylogenetic hypothesis places B. elegans as a basal form of Podocnemididae and is used to found a new biogeographic model for the Pelomedusoides. The biogeographical approach was performed with direct analysis of vicariance, using historical sequence of vicariance and phylogenetic information to construct an event-based model. Thus, inspection of distributions maps of Pelomedusoides and the phylogenetic arrangement proposed here were used to correlate cladogenesis and vicariance events during Cretaceous. Current biogeographic hypotheses suggest that living Pelomedusoides distribution and relationships could be the result of large-scale extinctions with extant taxa being relicts of a widespread group. The examination of relationships within Pelomedusoides allows the association of vicariance events of Gondwana fragmentation during the Cretaceous with the isolation of pelomedusoid lineages. We identified three vicariant events: the separation of northern Pelomedusoides and southern Chelidae (node of divergence of Chelidae); the isolation of Africa from Gondwana (node of divergence of Hamadachelys); and the separation of South America and India/Madagascar (node of divergence of Podocnemididnae and Erymnochelyinae). Extant Podocnemidinae (restricted to north South America) would derivate from a south South American source. Its ancestor would have had an autochthons development in South America, expanding its distribution northwards. The presence of Erymnochelyinae in Madagascar would be explained by the migration of a South American ancestor via Antarctica.