Dinocephalians are not anomodonts

Abstract

ABSTRACT Watson and Romer's (1956) proposal that dinocephalians, dicynodonts, and venjukoviomorphs comprise a monophyletic Anomodontia has been supported by King (1988) on the basis of four hypothesized synapomorphies: 1) loss of the coronoid bone, 2) non-terminal nostrils with a long posterior spur of the premaxilla, 3) a grooved palatal surface of the vomer, and 4) reduction or loss of the internal trochanter of the femur. These characters, however, appear to be plesiomorphic for therapsids (long internarial process of the premaxilla, and a grooved palatal surface of the vomer), related to incisor size and/or the degree to which the premaxillary alveolar margin is elevated, and show no consistent phylogenetic pattern (position of the external nares), homoplasies (convergent reduction or loss of the internal trochanter of the femur), or not even characteristic of dinocephalians (loss of the coronoid bone). There is no evidence to support inclusion of dinocephalians in the Anomodontia.