Compsemys

Compsemys was a moderately sized turtle, up to 30 cm (12 in) long, with a carapace covered with raised, flattened tubercles, which are not seen in any other turtle. This allows even small shell fragments to be identified as Compsemys. The skull resembles that of the alligator turtle, with a sharply hooked beak; Compsemys was likely an aquatic carnivore. it was suggested that some materials assigned to this genus are from the Santonian Milk River Formation of the Alberta and the Turonian Straight Cliffs Formation of the Utah, but Jasinski et al. (2026) suggested these are too incomplete to confidently refer to this genus. The morphology of the skull suggests that Compsemys was likely hypercarnivorous.

Its affinities have long been uncertain, but it has recently been considered to be the most basal member of Paracryptodira, despite the clade first appearing in the Late Jurassic, and is sometimes included in its own family, Compsemydidae. A revision in 2020 found Compsemydidae to be more expansive, also containing Riodevemys and Selenemys from the Late Jurassic of Europe, and Peltochelys from the Early Cretaceous of Europe.