The evolution of snake-like body form in squamate reptiles and the phylogeny and biogeography of the scincid genus Plestiodon

As evolution is essentially organismal change through time, all evolutionary biologists implicitly study nature in a temporal framework. However, recent methodological advances have enhanced our ability to incorporate evolutionary time into analyses of phylogenetics, morphology, and biogeography. Here, I apply time-calibrated phylogenies to explore one of the most dramatic body form transitions, the repeated evolution of limb reduction in squamate reptiles, across a time span of 180 million years. I demonstrate how time-calibrated phylogenies may be used to make inferences about the time frame over which major morphological transitions occur. I then focus on the scincid genus Plestiodon and utilize recent advances in modeling autocorrelated rates of molecular evolution (estimated by the use of fossil calibration age constraints) to infer the phylogeny of the genus and estimate when in history its constituent lineages diverged. Using these divergence time estimates, I reconstruct the historical biogeography of Plestiodon and simultaneously assess the potential difficulties of estimating molecular divergence dates and their potential solutions.