A well preserved pan-pleurodiran (Dortokidae) turtle from the English Lower Cretaceous and the first radiometric date for the Wessex Formation (Hauterivian–Barremian) of the Isle of Wight, United Kingdom

Abstract

The oldest record of a dortokid turtle (Testudines, Pan-Pleurodira) and the first occurrence of the group in the UK is reported. This find corresponds to the oldest pan-pleurodiran turtle in the country, and the only one from the Mesozoic of the UK. The new specimen, from the Lower Cretaceous (Barremian) Wessex Formation of the Isle of Wight, comprises a relatively complete shell with post cranial elements within a calcite-filled shell vacuity. Micro CT scanning has revealed these tiny bones to include cervical, dorsal and caudal vertebrae, scapulae, pelvic girdle and appendicular elements. In addition, aspects of the internal morphology of the carapace and plastron are revealed. No features allow the new specimen to be distinguished from the coeval Eodortoka morellana of Spain, and we therefore identify it as Eodortoka cf. morellana.The specimen was found ex-situ, and due to questions raised regarding the provenance of the specimen, U–Pb geochronology of the diagenetic calcite filling was performed to establish the age of the specimen. Previously, it has been challenging to determine absolute timing constraints for the Wessex Formation fossil material due to lack of minerals dateable with radiometric techniques. This analysis has thus provided the first radiometric date for the Wessex Formation of 127.3 ± 2.7 Ma.