Although numerous theories for the origins of the Ichthyosauria have been proposed, their relationship to other reptilian orders has never been satisfactorily resolved. This study will improve on previous work by (1) emphasizing features of Triassic species, which, surprisingly, were ignored by most hypotheses of ichthyosaurian affinities, and (2) examining a wider range of morphologic characters. An osteological study of Triassic ichthyosaurs will document the distribution of derived and primitive characteristics among these species. A comparative study with other early reptilian taxa will suggest affinities for the ichthyosaurs based on a wide range of morphologic features. Tooth form, general body shape, and the morphology of the axial skeleton and limbs will provide evidence for the prey preference and swimming capabilities of individual species. These data will be used to evaluate the range of predator types among the Triassic ichthyosaurs. Finally, a phylogeny for the Triassic ichthyosaurs will be proposed.
