Megaevolutionary dynamics in reptiles and the role of adaptive radiations in evolutionary innovation

Abstract Adaptive radiations are long believed to be responsible for the origin of phenotypic diversity and new body plans among higher clades in the fossil record. However, few studies have assessed rates of phenotypic evolution and disparity across broad scales of time to understand the evolutionary dynamics behind the origin of major clades, or how they relate to rates of molecular evolution. Here, we provide a total evidence approach to this problem using the largest available data set on diapsid reptiles. We find a strong decoupling between phenotypic and molecular rates of evolution, with many periods of accelerated phenotypic evolution or expansion of phenotypic disparity at the origin of major reptile clades and body plans that do not correspond to periods of adaptive radiation. We find heterogeneous rates of evolution during the acquisition of similarly adapted functional types, and that the origin of snakes is marked by exceptionally high evolutionary rates.