An early bothremydid from the Arlington Archosaur Site of Texas

The discovery of the oldest known North American species of side-necked turtle — turtles that withdraw their necks sideways into their shells when threatened — is reported in Scientific Reports this week. The findings suggest that side-necked turtles may have migrated to North America during the Cenomanian age (100 to 94 million years ago).

Brent Adrian and colleagues have named the species Pleurochayah appalachius from the Greek word Pleuro (side), the Caddo word Cha'yah (turtle) and the North American Appalachian region. The fossilised remains of P. appalachius, which were discovered at the Arlington Archosaur Site in the Woodbine Group in Texas, USA, date back to the lower middle Cenomanian. They predate remains of Paiutemys tibert, a side-necked turtle species from Utah that dates back to the late Cenomian and was previously recognised as the oldest known side-necked turtle from North America. The authors report a number of features that suggest P. appalachius may have been adapted for life in marine environments. Robust bony protrusions at the end of its humerus, which formed part of its shoulder joint, may have made its stroke more powerful when swimming. The thick outer surface of its shell bones may have strengthened the shell and protected P. appalachius in marine environments.

Analyses of the evolutionary relationships between turtle species suggests that P. appalachius was an early member of the Bothremydidae family of side-necked turtles that originated in the Gondwana supercontinent 145 to 100 million years ago. Based on these findings and the adaptations of P. appalachius to marine environments, the authors suggest that early Bothremydidae may have migrated from Gondwana to North America during or prior to the Cenomanian age via the central Atlantic Ocean or the Caribbean.