Article: The cranial osteology of the Middle Triassic ichthyosaur Contectopalatus from Germany

A new partial skull of the Middle Triassic ichthyosaur Contectopalatus atavus allows many new osteological observations and makes the referral of several additional specimens, including lower jaw material, possible. This aids very much in the understanding of the anatomy of this highly derived mixosaurid species. The lectotype of Ichthyosaurus atavus is shown to be diagnostic and the recent proposal of a neotype is unnecessary. Contectopalatus shows thecodont dentition in all parts of the jaws. The teeth are labyrinthodont at their bases. Some specimens, which are interpreted as very late ontogenetic stages of C. atavus, indicate that Contectopalatus grew very large, reaching four to five times the size of other mixosaurids. Mixosaurid taxonomy is reviewed. Three valid genera can be included in a monophyletic Mixosauridae: Mixosaurus (including M. cornalianus and M. kuhnschnyderi), PhalarodonContectopalatus (monotypic). The mixosaurids are the sister group to the remaining ichthyosaurs, apart from the Lower Triassic forms. The status of the Omphalosauridae remains unresolved, but they are not closely related to the mixosaurids, because the durophagous dentition was acquired convergently in the two groups.