A new podocnemidid (Pleurodira: Pelomedusoides) from the Eocene of north-western Argentina, with comments on its evolutionary relationships and palaeoenvironmental settings

Abstract

We report a new small podocnemidid, Gestemys powelli gen. et sp. nov., based on one nearly complete skull, lower jaw, two shells, and remains of the appendicular skeleton belonging to two specimens from the Eocene Geste Formation of the San Antonio de la Cobres Basin, Salta Province, north-western Argentina. As in other podocnemidid genera, Gestemys exhibits a fully developed and medially extensive cavum pterygoidei, an incisura columellae auris enclosing the stapes and Eustachian tube, and lacks an exoccipital quadrate contact. Gestemys powelli bears a huge foramen palatinum posterius and a short pterygoid flange that does not reach the basisphenoid suture, exposing the cavum pterygoid. Phylogenetic analyses place Gestemys powelli as a member of Podocnemididae more closely related to Erymnochelyinae than Podocnemidinae. In regards to the palaeoenvironmental settings of the Palaeogene formations (Maíz Gordo and Geste) of north-western Argentina, at least two features differentiate the palaeoenvironment where G. powelli was recovered and those of other podocnemidid turtles from the Maíz Gordo Formation: 1) G. powelli was found in situ with very little re-working; and 2) in contrast to the muddy rocks indicating the marginal lacustrine setting and humid climate of the Maíz Gordo Formation, G. powelli is associated with a coarse-grained floodplain setting and a dry, temperate climate. Such differences highlight the contrasting environmental dynamics in which podocnemidid turtles lived during the Palaeogene.

http://zoobank.org/urn:lsid:zoobank.org:pub:0E631DA2-053F-4BD6-91BD-2401F34A5777

Keywords:

• Palaeogene
• Geste Formation
• Puna
• South America
• turtles
• systematics
• palaeoenvironments

Acknowledgements

We thank Ivana Tapia (CICTERRA-CCT Córdoba-UNC) and Cristian Sancho (IANIGLA-CCT Mendoza) for the mechanical preparation of the postcranium and cranium of the turtle, respectively, and S. Hernández Del Pino (IANIGLA) for his valuable help in handling the study specimen at FUESMEN Nuclear Hospital in Mendoza city. We would like to give our thanks to the imaging department team at the FUESMEN nuclear hospital, particularly the tomographic technician Sergio Mosconi. E. Gaffney (American Museum of Natural History, New York) and F. de Lapparent de Broin (Muséum d´Histoire Naturelle, Paris) provided us with a skull cast of Podocnemis bassleri, and a skull and shell cast of Lapparentemys vilavilensis, respectively. We also extend our thanks to Editor-in-Chief Paul Barrett, as well as reviewers S. Evers and G. Ferreira, for their insightful comments and corrections that further improved the original manuscript. We also thank N. Basily and C. Corbitt (Louisville University) for the English proof-reading of the original manuscript. This paper was partially supported by PICT 2016-N°1274 to C. del Papa. C. del Papa and J. Lesdesma thank CICTERRA-PUE 2016 and Strategy program. Finally, we thank Leonardo Mercado and Patricia Camaño, from the Museum of Anthropology of Salta, Argentina, for giving fieldwork permission in the SAC area.

Supplemental Material

Supplemental material for this article can be accessed here: https://doi.org/10.1080/14772019.2022.2081939.

CT Scan and model available at: https://www.morphosource.org/projects/000436332?locale=en.

Associate Editor: Paul Barrett