Phylogeny of the chelydrid turtles : a study of shared derived characters in the skull / Gaffney, Eugene S. text Chicago : Field Museum of Natural History, 1975. eng p. 157-178 : 24 cm. The turtle genera Chelydra (Recent, North America), Macroclemys (Recent, North America), Platysternon (Recent, Asia), Protochelydra (Paleocene, North America), and Macrocephalochelys (Pliocene, Asia) are hypothesized as a strictly monophyletic group on the basis of a shared derived character study of the skull. The five genera are therefore placed in the Family Chelydridae. The primary characters used involved the degree of temporal and cheek emargination along with changes in bone size and shape in the skull roof. Protochelydra, with the most extensive emarginations is proposed as the primitive end of a morphocline series culminating in Platysternon, which has the least emarginate condition. Cranial diagnoses for the testudinoid families Chelydridae, Emydidae, and Testudinidae are included. Caption title. "August 18, 1975." "This volume is dedicated to Dr. Rainer Zangerl." Includes bibliographical references (p. 176-178). Fieldiana series has been published as Geological Series by Field Columbian Museum (1895-1909) and Field Museum of Natural History (1909-1943), and as Fieldiana: Geology by Chicago Natural History Museum (1945-1966) and Field Museum of Natural History (1966-). Snapping turtles Turtles -- Classification. Reptiles -- Anatomy Skull