In a forthcoming paper in MPE Alencar et al (2016) look at the diversification of vipers. The cosmopolitan family contains about 329 venomous species showing a striking heterogeneity in species richness among lineages. While the subfamily Azemiopinae comprises only two species, 70% of all viper species are arranged in the subfamily Crotalinae or the “pit vipers”. The radiation of the pit vipers was marked by the evolution of the heat-sensing pits, which has been suggested to be a key innovation for the successful diversification of the group. Also, only crotalines were able to successfully colonize the New World. The authors present the most complete molecular phylogeny for the family to date that includes sequences from nuclear and mitochondrial genes representing 79% of all living vipers. They also investigated the time of divergence between lineages, using six fossils to calibrate the tree, and explore the hypotheses that suggest crotalines have undergone an explosive radiation. The phylogenetic analyses retrieved high support values for the monophyly of the family Viperidae, subfamilies Viperinae and Crotalinae, and 22 out of 27 genera, as well as well-supported intergeneric relationships throughout the family. The study found strongly supported sister clade to the New World pit vipers that comprises Gloydius, Ovophis, Protobothrops and Trimeresurus gracilis. Time of divergence estimates suggested that vipers started to radiate around the late Paleocene to middle Eocene with subfamilies most likely dating back to the Eocene. The invasion of the New World may have taken place sometime close to the Oligocene/Miocene boundary. Diversification analyses suggested a shift in speciation rates during the radiation of a sub-clade of pit vipers where speciation rates rapidly increased but slowed down toward the present. Thus, the evolution of the loreal pits alone does not seem to explain their explosive speciation rates. The auithor suggest that climatic and geological changes in Asia and the invasion of the New World may have also contributed to the speciation shift found in vipers.
Alencar, L. R., Quental, T. B., Grazziotin, F. G., Alfaro, M. L., Martins, M., Venzon, M., & Zaher, H. (2016). Diversification in vipers: Phylogenetic relationships, time of divergence and shifts in speciation rates. Molecular Phylogenetics and Evolution.