for National Geographic News
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.
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