Integration of Bayesian molecular clock methods and fossil-based soft bounds reveals early Cenozoic origin of African lacertid lizards

According to the most reliable model, as indicated by Bayes factor comparison, modern lacertids arose shortly after the K/T transition and entered Africa about 45 million years ago, with the majority of their African radiation occurring in the Eocene and Oligocene. Our findings indicate much earlier origins for these clades than previously reported, and we discuss our results in light of paleogeographic trends during the Cenozoic.This study represents the first attempt to estimate evolutionary ages of a specific group of reptiles exhibiting uncertain phylogenetic relationships, molecular rate variation and a poor fossil record. Our results emphasize the sensitivity of molecular divergence dates to fossil calibrations, and support the use of combined molecular data sets and multiple, well-spaced dates from the fossil record as minimum node constraints. The bioinformatics program used here, TreeTime, is publicly available, and we recommend its use for molecular dating of taxa faced with similar challenges.The molecular clock [1] has become an increasingly common tool among biologists for dating the origins of species or lineages using genetic sequence data. This is commonly done by measuring the genetic distance between two species and, assuming mutations occur at a constant rate, applying an external calibration to convert those distances into geological time (for a review of molecular clock methods, see [2]). Despite its widespread application, calibration of the clock using independent evidence, typically derived from the fossil record, is still problematic for many groups. While proper calibration dates for major evolutionary events like the mammal-bird or fish-tetrapod split are under constant debate [3-6], less attention has been given to smaller, less inclusive clades, which often have poor fossil records. Such discussions would be particularly useful for evolutionary biologists since it is often these clades that are the subject of more detailed investigations