Meeting Abstract
Twenty-four species of crocodile populate the globe today, but this richness represents a minute fraction of the diversity and disparity of Crocodyliformes since their origin early in the Triassic. Across this clade, three major diversification events into the aquatic realm occurred. Aquatic and terrestrial habitats impose differing selective pressures on body size. However, previous research on this topic in Crocodyliformes remains qualitative in nature. In this study, our goal was to quantify the influence of habitat (terrestrial versus aquatic) on the evolution of body size in Crocodyliformes. By compiling an extensive body size database of fossil and modern crocs and using phylogenetic comparative methods, we find a history of repeated body size increase and convergence coupled with increases in strength of selection and decreases in variance following shifts to an aquatic lifestyle, suggesting common selective pressures on life in water spanning multiple independent aquatic clades. Lung volume, which has long been proposed as the main constraint on diving time, is only a constraint at sizes greater than 10 kg, whereas the rate of cooling constrains diving time at sizes less than 10 kg. Therefore, we propose this may be the primary driver of larger body sizes in aquatic crocodyliformes.
