Convergent evolution of the maxilla-dental-complex among carnivorous archosaurs

Abstract

Archosaurs first appeared in the Late Permian, and during the subsequent Mesozoic Era they evolved several different clades of carnivores, all of which can trace their origins back to a primitively carnivorous form. Three aspects of the maxillary teeth of carnivorous archosaurs were investigated for potential functional correspondences with the form of their associated maxillary bone: mean and maximal tooth lengths; medio-lateral and antero-posterior tooth bending strengths; and total external surface area of teeth. A fourth investigation looked at the depth of the skull relative to its length for any potential functional correspondence with total tooth area or mean maxillary tooth length. All linear and areal dimensions were normalized to correct for size-related factors. A good correspondence was found between long teeth and teeth with high bending strengths and the amount of bone in the ventral region of the maxilla; and this condition was observed to have evolved independently in rauisuchians, at least three times in theropod dinosaurs, and crocodylomorphs. No plausible relationship was found between the total surface area of the teeth and maxillary form. Working under the assumption that larger predators will generally attack and dismember larger prey, the observed changes in maxillary form are interpreted as a biomechanical response for increasing support of the teeth during a phylogenetic increase in body size, and the concomitant increase in the size of prey. A strong correlation also exists between normalized maxillary tooth lengths (mean tooth length divided by skull length) and skull aspect ratios (mean skull depth divided skull length). It is proposed that increases in the length of teeth, and the presumed increase in the depth of penetration by the teeth, are associated with an increased resistance to sagittal (dorso-ventral) bending of the skull for all sizes of carnivorous archosaurs.