"Cannibal" Dinosaur Wrongly Accused, Study Says
for National Geographic News
|September 25, 2006|
An infamous dinosaur "cannibal" that was long believed to have eaten its own young may have been given an undeserved reputation.
Coelophysis (SEE-loh-FIE-sis) were speedy, bipedal dinosaurs that roamed western North America more than 200 million years ago.
For nearly 60 years scientists have believed that fossils found in New Mexico showed juvenile Coelophysis skeletons in the gut contents of adults of the species.
(Read "Dinosaur Cannibal?—Mystery in New Mexico" [December 2002].)
But a new fossil study suggests that there is no proof that the meat-eating dino had an appetite for its own kind.
"Our research shows that the evidence for cannibalism in Coelophysis is nonexistent," said Sterling Nesbitt, a graduate student at Columbia University in New York City.
Nesbitt, who is also studying at the American Museum of Natural History's (AMNH's) division of paleontology in New York, co-authored the study.
The findings appear in the early online edition of the journal Biology Letters.
Croc, Not Baby, Bones
Coelophysis were turkey-size therapods—a group of bipedal meat-eating dinosaurs that includes Tyrannosaurus—that sported long legs, tails, and necks.
The beasts burst into the paleontology spotlight in 1947 when a trove of skeletons was unearthed near the Ghost Ranch site just north of Santa Fe, New Mexico (map of New Mexico)—apparent victims of some type of mass mortality.
The site contained hundreds if not thousands of Coelophysis skeletons, more than exist for any other dinosaur species.
Scientists found two individual animals on the site that appeared to have gut contents that included young of the same species.
The skeletons were too far developed to be unborn fetuses, so the late Edwin H. Colbert, chair of the department of vertebrate paleontology at AMNH, reached another conclusion.
Colbert determined that the remains were the last meals of larger Coelophysis—and dramatic evidence of dinosaur cannibalism.
For decades the find has been considered one of the very few examples of cannibalism among theropods.
But an odd-looking bone led researchers to revisit the Coelophysis case.
"You could see [the bone] on exhibition, and right from the beginning we felt that this didn't really look like a dinosaur," said Alan Turner, another Columbia University graduate student studying at AMNH.
The juvenile femur and other bones found in one of the accused Coelophysis's gut contents revealed leg and hip characteristics that are shared by crocodilians, not dinosaurs.
Studies of the femur's growth rate confirmed that it was crocodilian, because the reptiles exhibit very different growth characteristics from dinosaurs.
"I think it's pretty evident that this animal had not fed on its own young but on something else," said Peter Makovicky, dinosaur curator at the Field Museum in Chicago, Illinois.
The second animal's "last meal" may not have been a meal at all.
The study suggests that the gut contents were actually found outside the rib cage and were big enough to raise eyebrows.
"The [size of the] gut contents was very, very large and not likely to be a meal that this animal could have consumed," said AMNH's Turner.
It's possible that, during whatever calamity caused the mass deaths at Ghost Ranch, an adult dinosaur may have fallen on top of the remains of a juvenile beast.
If so, their bones could have mingled over the eons and created the mistaken impression that one animal had swallowed the other.
Given the new analysis, experts say that no one can be sure if therapod dinosaurs ever indulged in cannibalism.
"The best evidence was the Coelophysis find, and I think that's now largely refuted," said the Field Museum's Makovicky.
"It doesn't necessarily mean that Coelophysis would have not have acted cannibalistically given the opportunity. It just means that we're back to a state where we have no evidence."
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