Mesochelydia


Mesochelydia is a clade of stem-turtles, more inclusive than Perichelydia, but less than Testudinata. The clade is known from the Early Jurassic to the Present. The ancestral condition for Mesochelydia is thought to be aquatic, as opposed to terrestrial for Testudinata. They are distinguished from more basal Testudinatans by the presence of the following characters: strap like pectoral girdle, supramarginals absent, reduced posterior entoplastral process, eleven pairs of peripherals, elongate processus interfenestralis, paired basioccipital tubercles, fully formed cavum tympani and antrum postoticum, single vomer, confluent external nares, lacrimals and supratemporals absent.

Taxonomy

Additionally, an indeterminate basal non-Perichelydian Mesochelydian taxon is known from the Early Cretaceous Batylykh Formation in Russia.