Meeting Abstract
Morphological disparity can be generated during adaptive radiations in response to factors such as new resources, freedom from competition, and an absence of predators and pathogens. The oldest ancestor of the extant Australian radiation of agamid lizards (Amphibolurinae) arrived in Australia from Southeast Asia approximately 30 million years ago. Since then, Australian agamids have become a species-rich and ecologically diverse clade. Today, they are comprised of around 120 species distributed among every Australian habitat, and are particularly successful in arid environments. We have relatively sound knowledge of their taxonomic diversity and phylogenetic relationships, but their morphological diversity remains largely unexplored. Despite being such a taxonomically and ecologically diverse clade, their adaptive character has not been explicitly tested. Here, we use three-dimensional geometric morphometrics to characterise skull shape in Australian agamids and their Asian agamid relatives (Draconinae), and investigate the association between skull shape and ecological life habit. We find that in addition to phylogenetic affinity and evolutionary allometry, ecological factors play a major role in skull shape evolution of this clade, confirming their adaptive character. Through our evaluation of the cranial morphospace we find common themes of ecomorphology, where tree-dwelling species have long skulls and snouts, terrestrial species have short, blunt skulls, and saxicolous species have dorsoventrally flat skulls. These characteristics likely result from trade-offs to optimise functional capabilities, which often play a role in the evolution of skull shape.
