CRANIAL SHAPE VARIATION AND DISPARITY IN CROCODYLOMORPHA: ALLOMETRIC CHANGES AND THE INFLUENCE OF ECOLOGY

Crocodylomorpha, the group that includes living crocodylians and their extinct relatives, has a rich fossil record, with more than 200 million years of evolutionary history. This contrasts with the low diversity of crocodylians seen today, with only 27 modern species. Similarly, extinct crocodylomorphs exhibit much higher morphological disparity than extant taxa, as well as remarkable ecological diversity, ranging from fully marine to completely terrestrial forms. In this context, crocodylomorph cranial shape variation seems to be integrated with ecological factors (such as feeding strategies), given the biomechanical implications of skull elongation and shortening. However, the influence of ecology on crocodylomorph cranial shape was never comprehensively investigated. I used geometric morphometric techniques and phylogenetic comparative methods to analyze cranial shape variation and disparity in crocodylomorphs and to fully characterize its macroevolutionary patterns. I found a significant influence of ecological lifestyles (i.e. terrestrial, aquatic, and semi-aquatic) on cranial shape, as well as a strong size-shape relationship, indicating allometric shape changes (mainly in the snout region). Furthermore, I found that terrestrial species are more disparate (particularly notosuchians) and are usually small animals with short rostra. On the other hand, aquatic and semi-aquatic forms are usually associated with shifts to larger body sizes and more longirostrine macroevolutionary regimes. This suggests an intricate relationship between cranial shape, body size and ecology, and that clade-specific adaptations to different environmental conditions are determining large scale patterns of crocodylomorph cranial shape evolution.