Were Dinosaurs Cannibals?

majungasaurus
Two Majungasaurus going at it on Jurassic Fight Club (History Channel).

A few years ago, a paper published in the distinguished scientific journal Nature bore an arresting title: "Cannibalism in the Madagascan Dinosaur Majungatholus atopus." In it, researchers described their discovery of various Majungatholus bones bearing Majungatholus-sized bite marks, the only logical explanation being that this 20-foot-long, one-ton theropod preyed on other members of the same species.

(Since then, Majungatholus has had its name changed to the slightly less impressive Majungasaurus, but it was still the apex predator of late Cretaceous Madagascar.)

As you might have expected, the media went wild. It's hard to resist a press release with the words "dinosaur" and "cannibal" in the title, and Majungasaurus was soon vilified worldwide as a heartless, amoral predator of friends, family and children. It was only a matter of time before The History Channel featured a pair of Majungasaurus in an episode of its long-extinct series Jurassic Fight Club, where the ominous music and portentous narration made the offending dinosaur seem like the Mesozoic equivalent of Hannibal Lecter ("I ate his liver with some fava beans and a nice Chianti!")

Notably, Majungasaurus, aka Majungatholus, is the only dinosaur for which we have indisputable evidence of cannibalism. The only other genus that even comes close is Coelophysis, an early theropod that congregated by the thousands in the southwestern U.S.  It was once believed that some adult Coelophysis fossils contained the partially digested remains of juveniles, but it now appears that these were actually small prehistoric crocodiles like Hesperosuchus.

So Coelophysis (for now) has been cleared of all charges, while Majungasaurus has been pronounced guilty beyond a reasonable doubt. But why should we even care?

Many Creatures Will Be Cannibals, Given the Right Circumstances

The question that should have been asked upon the publication of that Nature paper wasn't "Why on earth would a dinosaur be a cannibal?", but rather, "Why should dinosaurs be different from any other animal?" The fact is that thousands of modern species, ranging from fish to insects to primates, engage in cannibalism, not as a flawed moral choice but as a hardwired response to stressful environmental conditions.

For example:

--Even before they're born, sand tiger sharks will cannibalize each other in the mother's womb, the biggest baby shark (with the biggest teeth) devouring its unfortunate siblings.

--Male lions will sometimes kill and eat the cubs of their rivals, in order to establish dominance in the pack and ensure the survival of their own bloodline.

--No less an authority than Jane Goodall noted that chimps in the wild will occasionally kill and eat their own young, or the young of other adults in the community.

This limited definition of cannibalism applies only to animals that deliberately slaughter, and then eat, other members of their own species. But we can expand the definition to include predators that opportunistically consume their packmates' carcasses--you can bet that an Africa hyena wouldn't turn up its nose at the body of a two-days-dead comrade, and the same rule doubtless applied to your average Tyrannosaurus Rex or Velociraptor.

Of course, the reason cannibalism evokes such strong feelings in the first place is that even supposedly civilized human beings have been known to engage in this activity. But again, we have to draw a crucial distinction: it's one thing for Hannibal Lecter to murder and eat his victims, and quite another for, say, members of the Donner Party to cook and eat already-dead travelers to ensure their own survival.

This (some would say dubious) moral distinction doesn't apply to animals--and if you can't hold a chimpanzee to account for its actions, you certainly can't blame a much more dim-witted Majungasaurus.

Why Isn't There More Evidence of Dinosaur Cannibalism?

At this point you may be asking: if dinosaurs were like modern animals, killing and eating their own young and the young of their rivals and gobbling down already-dead members of their own species, why haven't we discovered more fossil evidence? Well, consider this: trillions of meat-eating dinosaurs hunted and killed trillions of plant-eating dinosaurs during the course of the Mesozoic Era, and we've only unearthed a handful of fossils that memorialize the act of predation (say, a Triceratops femur bearing a T. Rex bite mark). Since cannibalism was presumably less common than the active hunting of other species, it's no surprise that the evidence thus far is limited to Majungasaurus--but don't be surprised if additional "cannibal dinosaurs" are discovered soon!