How the Turtle Got Its Shell — Ancient DNA Finally Revealed The Truth

For over 150 years, turtles were the most controversial group in vertebrate phylogenetics — the one clade that systematists simply could not agree on how to place. Based on the structure of their skull, which lacks the temporal openings found in other reptiles, they were classified for most of the twentieth century as the most primitive living reptiles — essentially unchanged since before the divergence of lizards, snakes, and archosaurs. Then morphological reanalysis placed them near lizards and snakes. Then near crocodilians. Then the molecular data arrived, and the debate ended. Turtles are the sister group to archosaurs: the clade containing crocodilians, and birds. A turtle is more closely related to a crocodile and to a sparrow than it is to a lizard, a snake, or a gecko. It took whole-genome sequencing to establish this with enough certainty to close the argument.