Dating the origin and diversification of Pan-Chelidae (Testudines, Pleurodira) under multiple molecular clock approaches

Pan-Chelidae (Testudines, Pleurodira) is a group of side-necked turtles with a currently disjointed distribution in South America and Australasia and characterized by two morphotypes: the long-necked and the short-necked chelids. Both geographic groups include both morphotypes, but different phylogenetic signals are obtained from morphological and molecular data, suggesting the monophyly of the longnecked chelids or the independent evolution of this trait in both groups. In this paper, we addressed this conflict by compiling and editing available molecular and morphological data for Pan-Chelidae, and performing phylogenetic and dating analyses over the individual and the combined datasets. Our totalevidence phylogenetic analysis recovered the Glade Chelidae as monophyletic and as sister group of a Glade of South American extinct chelids; furthermore Chelidae retained inside the classical molecular structure with the addition of extinct taxa in both the Australasian and the South American clades. Our dating results suggest a Middle Jurassic origin for the total Glade Pan-Chelidae, an Early Cretaceous origin for Chelidae, a Late Cretaceous basal diversification of both geographic clades with the emergence of long-necked lineages, and an Eocene diversification at genera level, with the emergence of some species before the final breakup of Southern Gondwana and the remaining species after this event.