The last marine pelomedusoids (Testudines:Pleurodira): a new species ofBairdemysand the paleoecology ofStereogenyina

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.

The Erymnochelys group of turtles (Pleurodira, Podocnemididae) in the Eocene of Europe: New taxa and paleobiogeographical implications

“…However, they show a hyaline tolerance, being morphologically partly adapted to marine locomotion (Renous et al, 2008). Through this means, Erymnochelyinae spread to America where it is represented by several species of Bairdemys Gaffney and Wood, 2002, identified from the upper Oligocene (early Chattian) record of South Carolina and the Mio-Pliocene of Maryland, Puerto Rico and Venezuela (Gaffney et al, 2011;Weems and Knight, 2013;Ferreira et al, 2015). In Western Asia, Erymnochelyinae is represented by the lower Miocene (Burdigalian) species Brontochelys gaffneyi (Wood, 1970) from Pakistan, and the Plio-Pleistocene Shweboemys pilgrimi Swinton, 1939 from Myanmar (Burma) (Wood, 1970;Gaffney et al, 2011;Barbière and Marivaux, 2015), species which might also have spread from Africa, following the coasts.…”

“…These taxa are Neochelys spp., 'Stereogenys' libyca, Albertwoodemys testudinum and 'Ste-reogenys' podocnemoides. 'Stereogenys' libyca is separated from the Shweboemys group sensu Broin (1988) and Lapparent de Broin (2000b) (i.e., Sterogenyina sensu Gaffney et al, 2011;Cadena, 2015a;Ferreira et al, 2015) by the continental shell pattern. No skull attributed to 'Stereogenys' libyca is known.…”

“…The skull of Stereogenys cromeri possessed a secondary palate that suggested an affinity of this genus with the taxa of the 'Shweboemys group' of Broin (1988) (i.e., Sterogenyina sensu Gaffney et al, 2011;Cadena, 2015a;Ferreira et al, 2015). Even so, its palate is recognized here as different from that of the 'Cordichelys-Bairdemys' morphotype present in all the other members of this littoral group, because its lateral palatine borders are not anteriorly divergent in the fossa inferior, but instead are parallel to the medial axis.…”

“…Medially, its posterior border is more abrupt, due to the development of short and straight to barely curved diverging borders. The corresponding lower jaw is more robust than in the 'Cordichelys-Bairdemys'morphotype, with a medially longer triturating surface (Andrews, 1903(Andrews, , 1906Gaffney et al, 2011;Ferreira et al, 2015). This more caudally and medially expanded Ste-reogenys morphology seems to be that of a feeding strategy of possibly hard prey crushing, stronger than the other morphotype, more similar to that of the extant cheloniids (Carr, 1952;Pritchard, 1979) and bothremydids (Lapparent de Broin and Werner, 1998;Gaffney et al, 2006).…”

Phylogeny, biogeography and diversification patterns of side-necked turtles (Testudines: Pleurodira)

“…[ 12 – 14 ]), as well as taxa adapted to marine (at least coastal) environments (e.g. [ 12 , 15 , 16 ]). The crown group includes three lineages with extant representatives, Chelidae, Pelomedusidae and Podocnemididae, and three extinct groups, Araripemydidae, Euraxemyidade and Bothremydidae [ 12 , 13 , 17 ].…”