Thalassemys bruntrutana n. sp., a new coastal marine turtle from the Late Jurassic of Porrentruy (Switzerland), and the paleobiogeography of the Thalassemydidae.

Christian Püntener,Jérémy Anquetin,Jean-Paul Billon-Bruyat

doi:10.7717/peerj.1282

Christian Püntener, Jérémy Anquetin + Show 1 more

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https://doi.org/10.7717/peerj.1282

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Journal: PeerJ	Publication Date: Sep 29, 2015
Citations: 21	License type: CC BY 4.0

Affiliation: Musée Cantonal d'Archéologie et d'Histoire

Abstract

Background. The Swiss Jura Mountains are a key region for Late Jurassic eucryptodiran turtles. Already in the mid 19th century, the Solothurn Turtle Limestone (Solothurn, NW Switzerland) yielded a great amount of Kimmeridgian turtles that are traditionally referred to Plesiochelyidae, Thalassemydidae, and Eurysternidae. In the past few years, fossils of these coastal marine turtles were also abundantly discovered in the Kimmeridgian of the Porrentruy region (NW Switzerland). These findings include numerous sub-complete shells, out of which we present two new specimens of Thalassemys (Thalassemydidae) in this study.Methods. We compare the new material from Porrentruy to the type species Th. hugii, which is based on a well preserved specimen from the Solothurn Turtle Limestone (Solothurn, Switzerland). In order to improve our understanding of the paleogeographic distribution of Thalassemys, anatomical comparisons are extended to Thalassemys remains from other European countries, notably Germany and England.Results. While one of the two Thalassemys specimens from Porrentruy can be attributed to Th. hugii, the other specimen represents a new species, Th. bruntrutana n. sp. It differs from Th. hugii by several features: more elongated nuchal that strongly thickens anterolaterally; wider vertebral scales; proportionally longer plastron; broader and less inclined xiphiplastron; wider angle between scapular process and acromion process. Our results show that Th. hugii and Th. bruntrutana also occur simultaneously in the Kimmeridgian of Solothurn as well as in the Kimmeridgian of England (Kimmeridge Clay). This study is an important step towards a better understanding of the paleobiogeographic distribution of Late Jurassic turtles in Europe.

Highlights

Thalassemys Rutimeyer, 1873 is a coastal marine turtle from the Late Jurassic of Western Europe (Bram, 1965; Lapparent de Broin F de, 2001)
In the present study we describe two new specimens of Thalassemys (MJSN SCR011-87 and MJSN BSY008-905) from the upper Kimmeridgian of Porrentruy, Canton of Jura, Switzerland
Thalassemys hugii, the type species, is based on a relatively complete shell associated with some postcranial elements (NMS 8595–8609) from the late Kimmeridgian of Solothurn, Switzerland (Rutimeyer, 1873; Bram, 1965)

Summary

INTRODUCTION

Thalassemys Rutimeyer, 1873 is a coastal marine turtle from the Late Jurassic of Western Europe (Bram, 1965; Lapparent de Broin F de, 2001). Puntener & Billon-Bruyat (2014) suggested that a strong anterior widening of the first neural was diagnostic for Thalassemys This feature is present in most specimens referred to Th. hugii, as well as in the type specimens of Th. marina and Th. bruntrutana. Isolated elements from Solothurn (e.g., NMS 22325) clearly indicate that Th. hugii possesses a lateral plastral fontanelle and an interdigitating contact between the hyoplastra (Anquetin, Puntener & Billon-Bruyat, 2014), refuting Bram’s reconstruction. We have detected new plastral material of Th. hugii from the St Niklaus quarry in the Solothurn collections (NMS 22286, NMS 22287, and NMS 22296; possibly from the same individual as NMS 22325) that confirm the observations of Anquetin, Puntener & Billon-Bruyat (2014), but it remains uncertain whether the hypoplastra met medially in Th. hugii, as in Th. bruntrutana and Th. marina. This falls within the range measured for Th. hugii and contrasts with the larger angle observed in Th. bruntrutana (Table 1)

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CONCLUSIONS