Turtles and crocs: Strange relations.

A new genetic study chops up the traditional reptile family tree by asserting that turtles are the closest living kin of crocodiles.

Generations of paleontologists have regarded turtles as outsiders among modern reptiles--holdovers from an ancient group called anapsids that lack holes in the sides of their skulls. Living reptiles and birds have two holes in the sides of their skulls and are termed diapsids. The new evidence, however, suggests that crocodiles are closer to turtles than they are to lizards, snakes, and birds--meaning that turtles sit smack in the middle of the reptile tree, rather than off to the side. S. Blair Hedges and Laura L. Poling of Pennsylvania State University in State College describe their work in the Feb. 12 SCIENCE.

These results confirm the findings from a previous molecular study that used fewer genes (SN: 12/5/98, p. 358). "It really solidifies the picture for the molecular data," says paleontologist Olivier C. Rieppel of the Field Museum of Natural History in Chicago. His own studies of fossil reptiles have also challenged the conventional interpretation of turtle origins.

Paleontologists will find other aspects of the genetic results perhaps even more disturbing than the news regarding turtles. Hedges and Poling provide some of the first DNA analysis of tuataras, a group of four-legged reptiles that look superficially like lizards and are regarded as their closest living relatives. The analysis by Hedges and Poling, however, places tuataras nearer to crocodiles than to lizards. "From a paleontological point of view, I cannot even begin to imagine how tuatara could not be [closely] related to lizards and snakes," says Rieppel.