A phylogeny and classification of the higher categories of turtles. Bulletin of the AMNH ; v. 155, article 5

Abstract

"Shared derived characters of the basicranium provide the basis for a new theory of relationships and a new classification of the major groups of living and extinct turtles. Post-Triassic turtles are characterized by a jaw-closing mechanism where the main adductor tendon rides over a trochlea, a condition unique among vertebrates. A study of the trochlear mechanism and associated basicranial adaptations for akinesis suggests that the trochlea evolved independently in cryptodires and pleurodires. Cranial arteries and the canals and foramina associated with them provide characters used to develop hypotheses of relationships among the Cryptodira. The taxon 'Amphichelydia,' characterized by primitive features and supposedly containing the ancestors of recent turtles, is rejected and its members distributed to monophyletic taxa"--P. 391.