"There is a two-headed tortoise at the Natural History Museum in Geneva [in Switzerland] which has lived there since it was born ten years ago," Buffetaut said.
There is no possibility that the new specimen was a two-headed species, he adds.
The hatchling belongs to a long-necked fish-eating species known either as Sinohydrosaurus or Hyphalosaurus that grew up to 3 feet (1 meter) long. Many one-headed specimens that otherwise resemble the fossil were found near the hatchling.
And no vertebrates have ever been reported to have two heads as their normal state.
"Having two heads obviously causes huge coordination and behavior problems, since it means having two brains which function more or less independently, while other organs within the body cavity, such as the heart and digestive tube, are usually not duplicated," Buffetaut said.
"Reptiles with two heads can survive for years in captivity because they are cared for, but in the wild they apparently don't survive very long."
Possible Hoax?
Buffetaut first learned of the fossil from study co-author Jianjun Li at the Beijing Museum in China.
The unusual nature of the fossil immediately aroused his suspicion—like many Chinese fossils, this was found by a local farmer and sold to a museum.
The isolated nature of such discoveries allows fakes to easily find their way to market—such as the Archaeoraptor fossil purported to be the missing link between carnivorous dinosaurs and birds in 1999.
Archaeoraptor was actually created by a Chinese farmer who intricately glued the front part of a fossil bird and the tail and hind legs of a small dinosaur together. (Read the full story: "Dino Hoax Was Mainly Made of Ancient Bird, Study Says" [November 20, 2002].)
In the case of the two-headed Choristodere, however, "the slab bearing the fossil is untouched and shows absolutely no sign of tampering, and neither do the tiny bones, so we are completely confident that the specimen is genuine," Buffetaut said.
Susan Evans is an evolutionary biologist at University College London in England and a leading expert on Choristodera.
"Two-headed mutants are fairly widely reported amongst modern reptiles, but this is the first reported occurrence of the phenomenon in a fossil reptile," she said.
"That certainly makes it interesting and worth reporting, and it gives us one more glimpse of Choristoderan biology."
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