Coelophysis acquitted of cannibalism?
8:12 pm
Is this the end of the Coelophysis Madonna? In a new paper in Biology Letters, Sterling Nesbitt et al. review the case for cannibalism in this Triassic dinosaur and, like a team of paleontological Perry Masons, they show how the very evidence presented against their dinosaurian defendant actually clears it of all charges.
The damning evidence
The most famous evidence for Coelophysis cannibalism comes from AMNH FR 7223/7224, a fossil slab that preserves the remains of two adult individuals. When these fossils were first prepared, AMNH curator Edwin Colbert noted several small bones within the ribs of both these animals. He interpreted these as the remains of juvenile Coelophysis that had been consumed by their cannibalistic elders. This interpretation has been repeated in scientific and popular literature, as well as in museum displays, television programs (not to mention stylish apparel). The authors of the paper took a closer a look at these specimens in order to evaluate this claim.
A last supper, or a knee to the gut?
The stomach area of AMNH FR 7223 contains a jumble of reptilian bones, none of which could be positively identified except for one—a juvenile Coelophysis legbone. While this would appear to be a clear-cut case of cannibalism, the authors raise a few concerns. The legbone is from a Coelophysis individual that was nearly two-thirds the size of AMNH FR 7223, and it is intact. It is difficult to envision how such a relatively large bone could have been swallowed whole. And while some of the ribs of AMNH FR 7223 lie on top of this pile of bones, none are preserved beneath it. So it is impossible to determine whether this mass of smaller bones actually came from inside the larger animal’s gut, or if they just happened to be what was preserved beneath AMNH FR 7223. (A similar point was made by researcher Rob Gay a few years back).
The Crocodile Hunter
The other fossil on the slab, AMNH FR 7224, does contain actual stomach contents—there are small bones preserved within the rib cage. But after looking carefully at the ingested remains, Nesbitt et al. failed to find any features that suggest they came from a juvenile Coelophysis. In fact, certain features of the bones were reminiscent of distant relatives of crocodiles, such as the contemporary crocodylomorph Hesperosuchus. In a CSI-worthy twist, they took the head of a femur from the stomach of AMNH FR 7224 and analyzed its histology, comparing its microstructure to femur samples from other Coelophysis and Hesperosuchus specimens. The histology confirmed their suspicions—AMNH FR 7224 was eating crocs, not kin.
Intestinal fortitude
So the evidence for cannibalism in Coelophysis is equivocal at best in AMNH FR 7223, and it actually acquits AMNH FR 7224 of all charges. But there is another piece of evidence suggesting that Coelophysis was a cannibal, and it comes from slightly farther along in the digestive tract. A team of researchers from the NMMNHS have reported on coprolites (fossil feces) and cololites (fossil intestinal casts) associated with Coelophysis skeletons from Ghost Ranch (Rinehart et al. 2005). Careful preparation of these elements has uncovered fragments of bone, some of which look very much like pieces of young Coelophysis fingers.
Nesbitt et al. , however, dismiss this evidence by stating that the bone fragments are, in their words, “taxonomically uninformative.”
Summation
This latest paper presents convincing arguments against the evidence for cannibalism in the AMNH Coelophysis specimens. I think the “cannibal coprolites” from the NMMNHS specimens merit a much closer look—then again, I’m somewhat biased. At this point, if I were sitting on a jury, forced to determine the guilt or innocence of Coelophysis in the heinous matter of baby-eating, my conscience would probably lead me to vote “not guilty.”
But I’d still be inclined to keep the story alive (and make a quick buck) by hawking sensationalist merchandise.
Further Reading
Nesbitt, S. J., Turner, A. H., Erickson, G. M., and Norell, M. A. 2006. Prey choice and cannibalistic behavior in the theropod Coelophysis. Biology Letters First Cite Early Online Publishing doi:10.1098/rsbl.2006.0524. PDF
Gay R. J. 2002. The myth of cannibalism in Coelophysis bauri. Journal of Vertebrate Paleontology 22, 57A.
Rinehart, L., Hunt, A., Lucas, S., Heckert, A., and Smith, J. 2005. New evidence of cannibalism in the Late Triassic (Apachean) dinosaur, Coelophysis bauri (Theropoda: Ceratosauria). Journal of Vertebrate Paleontology 25, 105A.
