A new species of soft-shelled turtle (Trionychidae) from the Middle Eocene of Ukraine

Abstract

Trionyx ikoviensis sp. nov., a new species of soft-shelled turtles (Trionychidae: Trionychinae), is established based on a partial but well preserved skull, isolated shell bones and cervical vertebrae VII and VIII from the Middle Eocene (Early Lutetian) Ikovo locality in the Luhansk Province of Ukraine. Trionyx ikoviensis cannot be assigned to any modern group within Trionychinae, but demonstrates most similarities with Trionychini (sensu Meylan 1987). Among fossil forms, T. ikoviensis is most similar to species of the genus Rafetoides and/or to some species of Trionyx sensu lato (sensu Lapparent de Broin 2001) from Europe with middle-sized carapace and long and wide jaws and snout, especially to Trionyx michauxi from the Lower Eocene of France. Although the taxonomic status and phylogenetic position of both Rafetoides and Trionyx sensu lato (sensu Lapparent de Broin 2001) need additional study, the latter assignment seems to be better corroborated. Trionyx ikoviensis is the easternmost representative of Trionyx sensu lato (sensu Lapparent de Broin 2001). Trionyx ikoviensis furthermore represents the first discovery of a trionychid skull in the Cenozoic deposits of the Ukraine in particular and the best discovery of this kind from the Cenozoic of the former USSR in general.