AN ALMOST COMPLETE JUVENILE SPECIMEN OF THE CHELONIID TURTLE CTENOCHELYS STENOPORUS (.

A new, unusually well-preserved juvenile specimen of Ctenochelys stenoporus from the Niobrara Formation is described. The skull has come apart at its sutures and all bones of the braincase and ear region are preserved three-dimensionally. This allows a detailed reconstruction of the important brain structures of a basal juvenile cheloniid turtle. It is compared with adult Ctenochelys specimens, and the major ontogenetic changes in the skull and postcranial skeleton are described. Furthermore, the specimen is compared with other fossil and extant cheloniids with well-known braincases and the differences between basal and advanced cheloniids turtles are specified. [ABSTRACT FROM AUTHOR]