Cannibalistic Dinosaur Theory Debunked

Sept. 26, 2006 — For a half-century a carnivorous dino called Coelophysis was believed to have a taste for juveniles of its own species. The idea — reiterated widely in museums, books and popular media — was based on two highly-touted 210-million-year-old Coelophysis fossils from New Mexico. These two fossils appeared to have bones of their own kind located where their stomachs used to be.

A new and closer examination of the bones, which are now located at the American Museum of Natural History in New York, has shown that one of these rare fossil dinos had actually died with a crocodile-like animal’s leg in its gut, while the other was merely buried atop a juvenile Coelophysis — giving the illusion that one was inside the other.

"It was an idea that needed testing," said Sterling Nesbitt, one of four museum researchers to take on the task of reexamining the fossils. Nesbitt and his colleagues have reported their iconoclastic results in the journal Biology Letters.

"It was the only real good evidence we had that these animals were cannibalistic," said Nesbitt. But Nesbitt said he grew more suspicious just looking at bronze castings of the famed Coelophysis fossils on display at the 81st Street subway station near the museum.

"They are really well-done casts," he said. "I could tell right away that the femur didn’t belong to a dinosaur."

To prove it, the original fossils were brought out of their glass case, and Nesbitt and his colleagues took thin sections of the bones to study under the microscope. What they found were telltale growth lines — rather like tree rings — which indicated a slow-growing early crocodilian, not a faster-growing dinosaur.

In the second case the "eaten" juvenile turned out to be outside the ribcage of the larger Coelophysis, not in its stomach cavity. What’s more, the juvenile was also just too big to have been eaten without killing the larger dino in the process, said paleontologist Raymond Rogers of Macalester College, St. Paul, Minn., who has searched for dino cannibalism elsewhere.

The juvenile would have had to displace all the internal organs of the adult to have fit, said Rogers. The matter was even pointed out a few years ago by a skeptical geology undergraduate named Robert Gay, of Northern Arizona University, Rogers said.

The five-decade-old misinterpretation of Coelophysis just shows how long an incorrect idea can persist and how important it is to re-examine evidence — especially if it is used to make extraordinary claims, said Rogers.

"I think that more than any other fossil group, there is a lot of speculation (about dinosaurs)," said Rogers. "Because they are so interesting and so popular, we’re more willing to go out on a limb." And sometimes the limb breaks.

On the other hand, the de-cannibalization of Coelophysis does not mean they did not eat each other, said Rogers. And Nesbitt agrees.

"I have no doubt that there was cannibalism in the dinosaurs’ 180-million-year history," said Nesbitt. After all, many animals living today turn cannibalistic at times — including humans. The problem is, he says, the chances of a fossil proving it are slim. It’s rare enough for a skeleton of an animal to be preserved as a fossil, let alone to preserve its last meal as well.

"I would argue that cannibalism never was prevalent," said Rogers. But since fossils are now very silent on the matter, "We’ll never know if cannibalism was common or rare."