Two-Headed Reptile Fossil From Age of Dinosaurs Found
for National Geographic News
|December 26, 2006|
Palaeontologists have found a tiny dinosaur-era reptile with two heads—the first time the extremely rare developmental anomaly has been found in a fossil.
The 120-million-year-old specimen, just 2.8 inches (7 centimeters) long, is a hatchling of a species of Choristodere—extinct aquatic reptiles resembling modern-day crocodiles or lizards.
Found in China, the fossil hatchling has two perfectly formed heads and necks fused at the base.
"When I saw it, I immediately realized it was something extremely unusual," said paleontologist Eric Buffetaut of the Centre National de la Recherche Scientifique (CNRS) in Paris, France.
"Two-headed reptiles are very rare, so the chance that one of them could get fossilized, preserved, and collected is extremely small," he added.
Buffetaut and Chinese colleagues detail their finding in the past week's issue of the journal Biology Letters.
Two Heads Not Better Than One
The developmental anomaly that causes animals to occasionally form two heads is called axial bifurcation.
The abnormality occurs when an embryo is damaged in the womb. A lesion can form, causing some parts to develop in duplicate.
The phenomenon, though quite rare, has been observed a number of times in modern-day reptiles, including lizards, snakes, turtles, and tortoises. (Related photo: "Two-Headed Turtle Found in China" [March 17, 2006].)
Scientists have even run across some two-headed mammals, such as sheep, though few survive to adulthood.
Two-headed reptiles are also at a significant disadvantage in the wild, but some have been know to live long lives in captivity.
"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."
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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