Basilemys

Basilemys ("king turtle" in Greek) is a large, terrestrial nanhsiungchelyid turtle from the Upper Cretaceous of North and Central America. Most fossils of Basilemys have been found in rocks dating to the Campanian and Maastrichtian subdivisions of the Late Cretaceous and is considered to be the largest terrestrial turtle of its time. In an analysis made by Sukhanov et al. on a nansiunghelyid turtle from the Upper Cretaceous of Mongolia, it was demonstrated that Asian nanhsiungchelyids gave rise to the North American nanhsiungchelyids.

Amongst nanhsiungchelyids, Basilemys is considered to be most similar to tortoises. Many paleontologists have described the behaviors of Basilemys to likely be comparable to that of tortoises, due to living in terrestrial habitats and consuming tough plants. Basilemys is easily distinguishable from other fossil turtles due to how thick its shell is, the intricate sculpture of rows of triangular tubercles separated by pits, and its reduced inframarginal scales. The fossil record is abundant with material from the shell, but cranial and cervical material is quite rare for Basilemys.