Scientists lift lid on turtle evolution
Family ties The turtle is a closer relative of crocodiles and birds than of lizards and snakes, according to researchers who claim to have solved an age-old riddle in animal evolution.
The ancestry of the turtle, which evolved between 200 and 300 million years ago, has caused much scientific squabbling - its physiology suggesting a different branch of the family tree than its genes do.
"The evolutionary origin of turtles has confounded the understanding of vertebrate evolution," the scientists write in a paper published in the Royal Society journal Royal Society Biology Letters.
Until the latest study, that is - which claims to have been the biggest of its kind.
"Our study conclusively shows that the genetic story is that turtles are more closely related to birds and crocodilians," says research team member Nicholas Crawford from >Boston University.
Anatomy and fossil studies of turtles and their reptilian relatives generally place the shelled creatures in the family of lepidosaurs - snakes, lizards and tuataras (rare lizard-like animals).
Genetic studies, however, say they have more in common with crocodiles and birds - which fall into the archosaur group of animals that also included the extinct land-bound dinosaurs.
The latter finding has now been confirmed by the most exhaustive genetic study on the topic ever done, says Crawford - having gathered "ten times as much" information as previous research efforts.
The team compared the DNA of the corn snake, the African helmeted turtle, the painted turtle, the American alligator, the saltwater crocodile, the tuatara, the chicken, the zebra finch and the Carolina anole lizard.
Crawford says the historic confusion partly arose because turtles shared key physical characteristics with lizards, snakes and tuataras - including a three-chambered heart. They had little in common with crocs and serpents. However, lepidosaurs and archosaurs are thought to share a common reptilian ancestor.