Abstract

A new genus and species of a chelid turtle (Calvarichelys coloniensis gen. et sp. nov.) from the Upper Cretaceous La Colonia Formation (Chubut Province, Argentina) is described here. This species is represented by an almost complete skull and a complete lower jaw. A detailed description and comparison of the species were made, recognizing a unique combination of characters that allow differentiating this species from the rest of stem and crown group Chelidae. Particularly, this new chelid is characterized by an almost non-existent temporal emargination with a lateral emargination reaching the parietals but leaving an extended skull roof with almost parallel margins. Also, this new species is similar to some Australasian (eg. Emydura macquarii, Elseya dentata) and South American (Platemys platycephala) short-necked chelids and some extinct chelids (e.g. Mendozachelys wichmanni) in the presence of a fused and hooked mandibular symphysis. Cladistic analyses were conducted to evaluate the phylogenetic relationships of the new species of turtle presented here. Three types of total evidence analyses were carried out under implied weights, equal weights, and using Bayesian inference.