The skull of the carettochelyid turtle Anosteira pulchra from the Eocene (Uintan) of Wyoming and the carotid canal system of carettochelyid turtles

Here we document the morphology of the only known skull of a carettochelyid turtle from North America. The specimen originates from the middle Eocene (early Uintan) Washakie Formation of Sweetwater County, Wyoming, and is referred to Anosteira pulchra based on temporal considerations. The skull of Anosteira pulchra broadly corresponds in its morphology to that of other carettochelyids but exhibits numerous differences that are related to it being more gracile. As a meaningful outgroup is lacking, it is not possible to determine if the gracile morphology seen in this taxon is apomorphic or plesiomorphic for the Anosteira-Allaeochelys clade. Anosteira pulchra and Carettochelys insculpta lack an ossified palatine canal. We conclude by reference to extant trionychids that the palatine (mandibular) canal is likely present but branches from the cerebral (pseudopalatine) canal following its exit from the sella turcica. As in trionychids, the vidian branch of the facial nerve (VII) of Anosteira pulchra and Carettochelys insculpta mostly traverses the palatine.