The Dinosaur on Trial for Cannibalism

Though the focus of my graduate studies was paleontology (the evolutionary history of crocodilians in particular), one semester I found myself in an anthropology course. As I churned through a vigorous workload, a single line from an assigned paper kept returning to me:  “There is nothing worse you can call someone than ‘cannibal.” I’m certain I don’t recall the exact wording, but the sentiment remains clear: In modern societies, cannibalism is among the most terrible of crimes.

Coelophysis  the cannibal. Illustration by Kate Dzikiewicz

Coelophysis the cannibal. Illustration by Kate Dzikiewicz

I think back to that anthropology class as I look at our newest science exhibit, Last Days of Pangea. We have many fascinating objects on display but there is one that has a particularly potent story to tell. In 1947, two Coelophysis skeletons were excavated from a mass death site. One of the dinosaurs had a jumble of small bones in its belly and the paleontologist Dr. Edwin Colbert identified them as belonging to a juvenile of the same species. Coelophysis was thus labeled a cannibal, and one that might even have devoured its own offspring.

Despite animals having no concept of law, the charge of cannibalism is still one that inspired revulsion. Dinosaurs were considered primitive and savage beasts at that time and this new discovery only validated that notion. As a testament to the infamy of the “cannibal Coelophysis,”our exhibit includes its cast on display. However, was it really a crazed cannibal, or could there be more to the story?

Click on the image for a closer look at the mystery bones within the rib cage. Photo by Paul Mutino

In 2002, the paleontologist Dr. Robert Gay took a closer look at the bones inside Coelophysis. The dinosaur had definitely eaten something, but he doubted that cannibalism was the appropriate diagnosis. The bones looked more like they belonged to another variety of small reptile. A few years later, another paleontologist would also question the status quo.

As our science curator Dr. Daniel Ksepka tells it, this new line of inquiry started at a subway station. Sterling Nesbitt, then a graduate student and now a professor at Virginia Tech, looked at a bronze cast of Coelophysis while waiting at the subway station for the American Museum of Natural History. What he saw agreed with Dr. Robert Gay’s assessment. The small bones in the dinosaur’s stomach definitely didn’t look like Coelophysis bones. He wanted to prove the dinosaur’s innocence beyond the shadow of a doubt, but first he had to get permission to perform destructive sampling on the specimen, a prospect often easier said than done.

We tend to think of fossilization as turning bones to stone, but the actual process is much more refined. Mineral replacement occurs so precisely that in many fossils the original microstructure of the bone is preserved. If you cut open a dinosaur bone you’ll see the exact same patterns and structures as you would have seen when the animal was alive. You can learn a lot about an animal’s growth and lifestyle by looking at the microstructure of its bones, so taking small slices of dinosaur bone is incredibly informative. They only problem with this method is that it requires damaging the fossil, and it can be hard to convince a curator that it’s worth the risk.

Images courtesy of Dr. Sterling Nesbitt

Images courtesy of Dr. Sterling Nesbitt

Fortunately, Nesbitt was granted permission to do some sampling. When he looked at thin slides of bones from the belly of Coelophysis his suspicions were confirmed. The microstructure of the bones didn’t look like Coelophysis, or even a dinosaur. They belonged to a small crocodile relative instead.

This wasn’t the only Coelophysis charged with cannibalism and the others were found equally innocent. In some cases, juvenile Coelophysis bones were determined to lie underneath the bones of adults, rather than inside their bellies. The process of being eaten and partially digested leaves telltale marks and none were found on any of the suspected cannibalized remains.

Coelophysis  attacking the crocodylomorph  Hesperosuchus . Illustration by Kate Dzikiewicz

Coelophysis attacking the crocodylomorph Hesperosuchus. Illustration by Kate Dzikiewicz

The verdict is in: Coelophysis was not a cannibal, at least not according to current fossil data. However, that doesn’t mean that cannibalism is uncommon or unnatural in the animal world. Subtypes of tiger salamander tadpoles will eat each other to knock out competition and gain nutritious meals. Mother animals from bears to rattlesnakes will eat their young in times of stress. A variety of insect and spider males willingly offer themselves as food to females during sex. Coelophysis may not have been a cannibal, but other dinosaurs were. Very specific tooth marks have been found on the bones of the large predatory dinosaur Majungasurus that could only have come from a member of its own species.

Cannibalism may be an abhorrent crime from a human perspective, but it can be a very adaptive behavior in nature. Our Coelophysis will be on display until July 16, so stop on by Last Days of Pangea and examine the evidence for yourself.  

- Kate Dzikiewicz, Paul Griswold Howes Fellow