Was This Dinosaur a Cannibal?

In 1947, paleontologist Edwin Colbert made a fascinating and grim discovery at a site in northern New Mexico known as **Ghost Ranch**. While exploring the high desert landscape, he and his team unearthed the remains of hundreds of meat-eating dinosaurs, all found in the same spot. Over the next five years, Colbert and his colleagues extracted 13 massive blocks of rock, each teeming with dinosaur skeletons. Interestingly, most of these fossils belonged to a single species, **Coelophysis**, a small, three-meter-long carnivorous dinosaur that lived during the late Triassic period, around 205 million years ago. Since that initial discovery, more than a thousand Coelophysis specimens have been uncovered at Ghost Ranch.

The discovery of such a large number of dinosaurs at a single site has puzzled paleontologists for decades. The cause of their death remains a mystery, though it’s hypothesized that a flood may have washed their bodies together after they died. However, it wasn’t just the number of fossils that baffled researchers. Among the remains of the Coelophysis, two adult skeletons revealed something strange: both had clusters of small bones inside their body cavities. These bones didn’t belong to the adults but appeared to be the remains of other smaller Coelophysis. Colbert interpreted this as evidence of **cannibalism**, a behavior commonly observed in the animal kingdom but never before documented in dinosaurs.

For years, Colbert’s findings spurred debate among paleontologists, as the implications of cannibalism in Coelophysis would offer rare insights into the behavior of dinosaurs. Since it is challenging to glean behavioral patterns from the fossil record, studying evidence of cannibalism could help paleontologists understand how extinct dinosaurs, particularly non-avian ones, might have behaved differently from their modern descendants, birds.

### **The Cannibalism Hypothesis**

Colbert’s initial interpretation of the small bones found inside two adult Coelophysis skeletons led him to suggest that the dinosaurs were cannibalistic. He based his conclusions on observations made in one specimen, which was preserved lying on its right side. Beneath its ribs on the left side, Colbert spotted a leg bone that appeared to belong to a juvenile Coelophysis, along with articulated vertebrae and other bone fragments. Another adult Coelophysis was found lying on its left side, with more reptilian bones inside its abdominal cavity. Colbert believed these findings pointed to cannibalism, where adult Coelophysis preyed on their own young.

Colbert's 1989 paper on the subject brought considerable attention to the idea that Coelophysis engaged in cannibalism. This concept became popularized in documentaries, books, and museum exhibits, portraying the dinosaur as an opportunistic predator that wouldn’t shy away from eating its own kind.

### **Reevaluating the Evidence**

In the early 2000s, paleontologist **Robert Gay** revisited the Ghost Ranch fossils and cast doubt on Colbert’s cannibalism hypothesis. Upon examining the supposed juvenile leg bone found inside the adult Coelophysis, Gay noticed its large size. The leg was over 13 centimeters long, which seemed too big for an adult Coelophysis to have swallowed whole. Further studies on the specimen suggested even more problems with the cannibalism interpretation. If the adult dinosaur had indeed swallowed the leg bone, the fossilized remains should have been positioned between its left and right ribs, where the stomach would have been. However, this wasn’t the case. The ribs on one side of the skeleton lay over the bones, but the ribs on the other side were displaced. Researchers now believe that the dinosaur’s abdominal cavity may have **exploded** after death due to gases building up or the weight of the sediment above it. This rupture would have disturbed the arrangement of the bones, making it difficult to determine whether the leg bone had truly been ingested.

As for the second adult Coelophysis specimen, its left and right ribs did encase some bones in the abdominal cavity, and its **gastroliths** (rib-like bones found in the bellies of many dinosaurs) were still intact. This suggested that this dinosaur’s body had not ruptured after death, making it more likely that the bones inside the abdominal cavity were indeed part of its last meal. However, a closer examination of those bones revealed that they didn’t belong to another Coelophysis. Instead, the bones closely resembled those of **Hesperosuchus**, a small reptile related to modern crocodiles. This new evidence cast further doubt on the idea that Coelophysis was cannibalistic.

### **The Cannibalism Debate Takes a Turn**

Just when it seemed that the idea of Coelophysis cannibalism had been debunked, a new discovery complicated the debate. While examining a separate block of Coelophysis fossils from Ghost Ranch, a team of paleontologists from the **New Mexico Museum of Natural History and Science** uncovered a peculiar trace fossil—a lump of prehistoric poop, or **coprolite**, wedged between the hip bones and base of the tail of one of the adult skeletons. This coprolite contained numerous bone fragments, including wrist and hand bones that appeared to come from juvenile Coelophysis. The placement of the coprolite suggested that it may not have been excreted, but rather preserved as a **cholelite**, a mass of partially digested material trapped inside the body.

In addition to this evidence, the same team discovered what might be **fossilized dinosaur vomit**, or **regurgitalites**, near another adult Coelophysis. These rare fossils appeared to contain tiny teeth resembling those of a young Coelophysis. Taken together, these findings suggested that Coelophysis might have engaged in cannibalism after all, potentially eating its own young. While some researchers remain skeptical, the discovery of fossilized feces and vomit has reignited the debate over Coelophysis’s feeding behavior.

### **Cannibalism in Other Dinosaurs**

Coelophysis isn’t the only dinosaur that might have engaged in cannibalism. Another well-known example is **Majungasaurus**, a six-meter-long theropod that lived in Madagascar during the late Cretaceous period. Some Majungasaurus fossils show bite marks that perfectly match the shape and placement of the dinosaur’s own teeth. Since no other large carnivores have been found in the same fossil beds, paleontologists believe that Majungasaurus may have regularly fed on members of its own species.

Similarly, evidence of cannibalism has been found in **Tyrannosaurus rex**. A 2010 study of T. rex fossils identified bite marks on several specimens that matched the size and shape of T. rex teeth. These bite wounds were found on bones that showed no signs of healing, indicating that they were inflicted post-mortem. This suggests that T. rex may have scavenged the remains of other T. rex individuals.

### **Why Did Dinosaurs Cannibalize?**

If Coelophysis, T. rex, and other dinosaurs did indeed engage in cannibalism, the reasons for this behavior could vary. Some modern-day animals resort to cannibalism when food is scarce, while others use it as a strategy to reduce competition. For example, American alligators have been known to eat juveniles of their species to limit future competition. In some species, cannibalism also serves as a form of population control.

It’s unclear whether dinosaurs actively hunted members of their own species or simply scavenged their corpses. However, the evidence of cannibalism in non-avian dinosaurs stands in contrast to their avian relatives. While cannibalism is widespread in the animal kingdom, including among reptiles and mammals, it is exceedingly rare in modern birds. Only a few bird species, such as herring gulls and some birds of prey, have been observed cannibalizing in the wild. The rarity of this behavior in birds raises intriguing questions about the differences between avian and non-avian dinosaurs.

### **Conclusion**

The decades-long debate over cannibalism in Coelophysis is a reminder of how much we still have to learn about the behavior of extinct dinosaurs. Through careful examination of fossils and trace evidence like coprolites and regurgitalites, paleontologists are continually uncovering new clues that bring us closer to understanding the lives of these ancient creatures. As more fossils are discovered and new technologies are applied to their study, we may one day unravel the mystery of whether Coelophysis and other dinosaurs truly feasted on their own kind.