The Evolution of the Crocodilia: A Conflict Between Morphological and Biochemical Data

Abstract

Recent investigations into the evolution of the living Crocodilia, belonging to the suborder Eusuchia, have revealed that the genus Gavialis may be its most primitive living member. New morphological studies have shown that the braincase structure, neural pocket, air sinus systems, jaw adductor mechanisms, pelvic and hindlimb morphology and epaxial musculature of the caudal region of Gavialis gangeticus do not correspond to the rest of the living Eusuchia. Contrary to the morphological findings, recent biochemical studies suggest a sister group relationship between Gavialis gangeticus and Tomistoma schlegelii, another longirostrine eusuchian. Judged by its morphology, Tomistoma is merely another member of the genus Crocodylus within the Eusuchia. This conflict in data either means that not enough of the genome of both Gavialis and Tomistoma is known, the shared genome represents the primitive states for these genes or that similar genotypes can give rise to rather different morphologies. As Gavialis resembles in some ways a Mesozoic level of organization it is considered to be a surviving eusuchian relict.