Oct. 2, 2006 Four American Museum of Natural History paleontologists have overturned a 1950s claim that a theropod dinosaur called Coelophysis was a cannibal that ate juveniles of its own kind, forcing a revision of a popular story of dinosaur behavior that has been repeated many times in the scientific literature, popular media, and museum exhibits.
In order to test the well-known cannibal-Coelophysis hypothesis, the team re-examined the anatomy of the two celebrated Coelophysis fossils said to exhibit cannibalism, as well as the structure of the bone found in the abdominal cavity of one of the specimens (the complete specimens are on permanent display in the Museum's Hall of Saurischian Dinosaurs).
In one specimen, the Museum scientists found that the carnivorous dinosaur's last meal was a primitive crocodile, not a dinosaur of any kind, let alone a Coelophysis; in the second specimen, the new analysis shows that the remains identified as a last meal actually are located outside the larger animal's ribcage and are possibly too large to have been eaten whole.
The adult dinosaur's skeleton probably was crushed on top of juvenile remains, creating the illusion that the remains were inside the gut of the adult dinosaur. And the Museum team found that the "gut content" bones actually are too shapeless to be identified as belonging to any dinosaur, or specifically a Coelophysis. They can only be identified as belonging to a sauropsid, a group of vertebrate animals that includes all modern and most extinct reptiles, including non-avian dinosaurs, pterosaurs, plesiosaurs, and others.
Overall, the anatomical findings, and a review by the researchers of remaining claims of cannibalism in theropod dinosaurs, fail to support the claim that Coelophysis was a cannibal and suggest that cannibalism in non-avian theropod dinosaurs in general was much more rare than previously thought. Agalychnis calcarifer Sterling Nesbitt inspecting the Coelophysis slab Credit: Mick Ellison, AMNH
The new research is described in the peer-reviewed journal Biology Letters by Sterling J. Nesbitt and Alan H. Turner, graduate students enrolled at Columbia University who study in the American Museum of Natural History's Division of Paleontology; Gregory M. Erickson, Assistant Professor of Anatomy and Vertebrate Paleobiology at Florida State University and a Research Associate at the Museum; and Mark A. Norell, Curator in the Museum's Division of Paleontology.
"Our research shows that the evidence for cannibalism in Coelophysis is non-existent, and the evidence for cannibalism in other theropod dinosaurs is quite thin. These findings offer new insight into the behavior of some of the earliest dinosaurs," Mr. Nesbitt said. "We hope to examine additional theropod fossils found at the location where these fossils were found to learn more about their prey choices."
The two specimens were unearthed in 1947 by crews from the Museum as part of an enormous bed of hundreds of skeletons of the early theropod Coelophysis bauri from the Upper Triassic (210 million years old) found near Ghost Ranch in north-central New Mexico. Soon thereafter, the two Coelophysis specimens that are the focus on this new research were prepared as a single fossil slab and revealed groups of small reptile bones that appeared to lie within the dinosaurs' body cavities.
The late Edwin H. Colbert, Curator of Fossil Reptiles and Chairman of the Department of Vertebrate Paleontology at the Museum from 1930 to 1970, asserted that the remains represented juveniles of Coelophysis and presented this as evidence of dinosaur cannibalism, generating the finding that was repeated over the years. [Dr. Colbert died in 2001, ending a rich academic career of more than 70 years that helped popularize the study of dinosaurs.]
"Cannibalism is seen among carnivorous animals today, but isn't common in living dinosaurs--birds. The behavior is really only prevalent among colonial sea birds and birds of prey," Mr. Turner said. "This made us wonder just how widespread cannibalism was among non-avian dinosaurs, and the case for Coelophysis was the strongest."
These questions led the Museum team to test the cannibal-Coelophysis hypothesis and conduct the anatomical analysis that overturned the claim of cannibalism. Along with the anatomical work, the research involved taking thin histological sections from the juvenile femur, or thigh bone, found in the gut of one of the specimens and comparing them with thin sections from the femurs of another Coelophysis specimen and from an early crocodile relative (crocodylomorph). The samples were used to determine how the animals' bones grew, and the results showed that the bone from the Coelophysis's gut grew like the crocodylomorph bone grew, not like the dinosaur bone grew, confirming the anatomical conclusion that this Coelophysis specimen was not a cannibal.
While there is evidence to suggest that cannibalism exists among theropod dinosaurs, the team re-examined the few other cases of "cannibalism" in Coelophysis and found that they were based on indirect evidence, such as digested material and intestinal casts, that reveals too little detail to support a claim of cannibalism. Similarly, claims for cannibalism in other theropods are based in part on tyrannosaur bite marks on the remains of tyrannosaurs from the Dinosaur Park Formation of Alberta but there are at least two species of tyrannosaurs in this location, so it cannot be concluded definitively that these tyrannosaurs ate their own. One piece of evidence for cannibalism in theropods remains--bite marks and teeth associated with Majungatholus atopus.
"In order for paleontology to continue to advance at the rapid pace that it has in the past two decades, it is important that paleontologists at the Museum and beyond continue to test hypotheses and assumptions made about dinosaur diversity and biology, including those about cannibalism," Dr. Norell said. "Our recent work, including this latest research on prey choice among theropod dinosaurs, reaches across many disciplines involving paleontologists, biomechanical engineers, physiologists, and others, and is revolutionizing our understanding of the mysterious lives of dinosaurs."
The work on the Coelophysis specimens was funded by the National Science Foundation and the American Museum of Natural History. The thin section (histological) analyses also were supported by the National Science Foundation.
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