The last marine pelomedusoids (Testudines: Pleurodira): a new species of Bairdemys and the paleoecology of Stereogenyina.

Gabriel S Ferreira,Max C Langer,Ascanio D Rincón,Andrés Solórzano

doi:10.7717/peerj.1063

Gabriel S Ferreira, Max C Langer + Show 2 more

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https://doi.org/10.7717/peerj.1063

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Abstract

The extinct Stereogenyina turtles form a relatively diverse Podocnemididae lineage, with twelve described and phylogenetically positioned species. They are characterized by a wide geographic and temporal range, from the Eocene of Africa to the Pleistocene of Southeast Asia, and a peculiar palate morphology, with a secondary palate that is unique among side-necked turtles. Here, we describe a new Stereogenyina species, based on an almost complete skull from the middle Miocene Capadare Formation, of Venezuela. A new phylogenetic analysis supports the assignment of the new species to the genus Bairdemys. Based on geometric morphometrics analyses, we related the development of the stereogenyin secondary palate with the acquisition of a durophagous diet. Based on a review of the sedimentary environments where their fossils are found, we also propose that stereogenyins were a marine radiation of podocnemidid turtles, as corroborated by previous studies of fossil eggs and limb morphology. These two inferences allowed us to hypothesize that stereogenyins occupied an ecological niche similar to that of the extant Carettini sea turtles, and that the rise of the latter group may be related to the Stereogenyina diversity fall in the end of the Miocene.

Highlights

The Stereogenyina is a peculiar extinct podocnemidid lineage, promptly recognized among pleurodiran turtles by their unique secondary palate, with a midline cleft formed by the maxilla and the palatine (Gaffney et al, 2011)
Nomenclatural acts The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Commission on Zoological Nomenclature (ICZN), so that the new names contained in the electronic version are effectively published under that Code from the electronic edition alone
In a recent phylogenetic analysis (Menegazzo, Bertini & Manzini, 2015), the only one to include “B.” healeyorum, that taxon was placed as sister to B. venezuelensis + B. hartsteini

Summary

Introduction

The Stereogenyina is a peculiar extinct podocnemidid lineage, promptly recognized among pleurodiran turtles by their unique secondary palate, with a midline cleft formed by the maxilla and the palatine (Gaffney et al, 2011). Six of the twelve known stereogenyin species have been formally assigned to Bairdemys (Weems & Knight, 2013), a genus known from the Oligocene of the USA to the Miocene of Puerto Rico and Venezuela. They are characterized by the curved edges of the secondary palate midline cleft, and the very small, slitlike opening of the antrum postoticum (Gaffney et al, 2008). The first known taxon of this group was described by Wood & Dıaz de Gamero (1971) as Podocnemis venezuelensis, from the late Miocene Urumaco Formation, Venezuela. It was inferred as possibly corresponding to a marine turtle, on the basis of the depositional environment of the type locality (Wood & Dıaz de Gamero, 1971), as supported by further evidence (Winkler & Sanchez-Villagra, 2006; Smith et al, 2010)

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