Environmental drivers of body size evolution in crocodile-line archosaurs

Ever since Darwin, biologists have debated the relative roles of external and internal drivers of large-scale evolution. The distributions and ecology of living crocodilians are controlled by environmental factors such as temperature. Crocodilians have a rich history, including amphibious, marine and terrestrial forms spanning the past 247 Myr. It is uncertain whether their evolution has been driven by extrinsic factors, such as climate change and mass extinctions, or intrinsic factors like sexual selection and competition. Using a new phylogeny of crocodilians and their relatives, we model evolutionary rates using phylogenetic comparative methods. We find that body size evolution follows a punctuated, variable rate model of evolution, consistent with environmental drivers of evolution, with periods of stability interrupted by periods of change. Regression analyses show warmer environmental temperatures are associated with high evolutionary rates and large body sizes. We confirm that environmental factors played a significant role in the evolution of crocodiles.
Stockdale and Benton use a new phylogeny of living and extinct crocodilians and their closest relatives to model evolutionary rates and identify the relative influences of extrinsic and intrinsic drivers of evolution in this order. Their results show that environmental factors played a significant role in the evolution of crocodiles.