Schism in the house of reptiles.

Schism in the house of reptiles

Most people know that snakes, lizards, crocodiles and turtles fit together under the category of reptile. But new evidence about the ancestry of turtles suggests that these armored animals come from evolutionary stock very different from that of other reptiles, a finding that challenges standard beliefs about reptile origins.

Paleontologists trace reptilian history back to an ancient group of animals called captorhinids, which lived during the Permian period from around 280 million to 250 million years ago. Taxonomists have traditionally tossed turtles and tortoises in with the other reptiles, linking them all to the captorhinids. Yet scientists actually know little about the evolutionary history of turtles prior to 200 million years ago, the age of the oldest known turtle fossil.

In the Jan. 24 NATURE, Robert R. Reisz and Michel Laurin challenge the captorhinid connection, proposing instead that turtles and tortoises more closely resemble an ancient group of land creatures called procolophonids. The researchers, both at the Erindale Campus of the University of Toronto, base their hypothesis on an examination of two recently discovered specimens of a primitive procolophonid called Owenetta, found in 245-million-year-old rocks from South Africa. They note that turtles share substantial anatomic similarities with Owenetta, indicating a close relationship between the two groups. Reisz and Laurin do not believe turtles evolved directly from Owenetta; rather, they suggest that the first turtles and Owenetta are more like cousins descended from an unknown common ancestor, which presumably lived several million years before Owenetta's time. If true, this theory suggests that turtles do not share close ties with other living reptiles.