Pit vipers, represented by this Ridge-nose Rattlesnake were once thought to have evolved quite recently. Now, based on the DNA clock they are estimated to have first evolved about 35.6 million years ago. Today there are about 200 species of pit vipers. But the colubrines evolved about the same time and have more than 600 species. In a forthcoming paper Pyron and Burbrink investigate why some clades of snakes are species rich, and others are species poor. JCM |