The skull of the carettochelyid turtle <i>Anosteira</i> <i>pulchra</i> 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.

Holotype snout elements of Saniwa ensidens reassigned to cf. Restes sp. indet (Xenosauridae)

During the field season of 1870, F. V. Hayden collected a number of sandstone blocks that contained the remains of a large fossil lizard (Middle Eocene Bridger Formation, Sweetwater County, Wyoming). Though mostly unprepared, the visible bones were described by Leidy (1870) as Saniwa ensidens (USNM 2185; holotype). Fifty years later all the blocks associated with USNM 2185 were prepared prior to Gilmore's (1922) more complete description of Saniwa ensidens and his assignment of the taxon to the Varanoidea. Gilmore (1922) notes that the skeletal remains in the blocks were partially disarticulated to dissociated despite the excellent articulation of some components (e.g., palatal elements and right and left maxillary fragments [Gilmore, 1922, p. 809; pl. 1). Gilmore (1928) altered the diagnosis of Saniwa ensidens (USNM 2185) by adding characterizations of a premaxilla, right and left anterior maxillary fragments, and anterior tips of the dentaries. Gilmore (1928, p. 57) stated that these missing elements were found after further preparation of the blocks when the type specimen was mounted for display.