In 1947, paleontologist Edwin Colbert made a grim discovery at a site in northern New Mexico known as Ghost Ranch.
While exploring the high desert, he and his companions uncovered the remains of hundreds and hundreds of meat-eating dinosaurs that all died at the same spot.
For five years, Colbert and his crew removed thirteen massive blocks of rock, each of which was jam-packed with dinosaur skeletons.
And strangely enough, the vast majority of those fossils were of the same animal: Coelophysis, a three-meter-long carnivore that lived 205 million years ago, in the late Triassic period.
All told, at least 1,000 specimens of Coelophysis have turned up at Ghost Ranch since 1947.
Nobody knows why--or how--this many dinosaurs of the same species all came to rest here.
But it seems that after they died, their bodies were washed together, possibly by a flood.
And the dinosaurs’ cause of death wasn’t the only mystery that Ghost Ranch had to offer.
There was something strange about two of the adult skeletons.
Both of them had jumbled masses of small bones-- bones that didn’t belong to them--lodged inside their body cavities.
To Colbert, these bones looked suspiciously like the remains of other, smaller Coelophysis.
Colbert interpreted this as evidence of a phenomenon that’s quite common in the natural world, but had never before been found in dinosaurs: cannibalism.
Paleontologists have spent the better part of two decades debating whether Colbert was right -- whether Coelophysis did, in fact, eat its own kind.
And while it still has its camps on both sides, the debate is important for a lot of reasons: For one thing, the studies of these dinosaurs have given us some very rare clues about dinosaurs’ actual behavior, something that’s almost impossible to glean from the fossil record.
And insights into that behavior may shed light on how extinct dinosaurs may have differed from modern-day dinosaurs, also known as birds.
But most of all, the evidence that scientists have had to study in order to answer the cannibalism question includes some of the strangest and grossest fossils that any expert would ever get to see.
If you want to study cannibalism in dinosaurs, it turns out, you need to examine not just chewed-up bodies, but also fossilized poop, ruptured stomachs, and even ... prehistoric vomit.
Cannibalism is widespread throughout the animal kingdom.
From polar bears to octopuses, well over a thousand living species are known to do it.
And animal cannibals can have lots of different motivations.
When a male lion takes over a new pride, for example, he may devour existing cubs in order to make their mothers reproductively available again.
Mormon crickets, meanwhile, cannibalize each other to get more protein and salt in their diets during their long migrations.
And in a study of Mexican lance-headed rattlesnakes, 68% of the females were found to eat their own stillborn young -- possibly as a way for the mothers to replenish themselves after exhausting pregnancies.
Because there are so many cannibal species alive today, it might be reasonable to think that some non-avian dinosaurs ate their own, too.
But here’s the thing: Today’s living dinosaurs--birds--almost never engage in cannibalism in the wild.
Very few species have ever been observed doing it; herring gulls and some birds of prey are rare exceptions.
So if birds aren’t prone to this behavior, a lot of researchers are interested in whether non-avian dinosaurs were.
Because, the answer could tell us a lot about the relationships between the two groups.
And when Colbert examined those two Coelophysis adults from New Mexico, he thought he’d found some compelling evidence of cannibalism.
For example, one of the dinosaurs he found had been preserved lying on its right side.
And under the ribs on the creature’s left flank, Colbert spotted the leg bone of what may have been a juvenile Coelophysis.
He also found some articulated vertebrae and some fragmented bones below those ribs.
Meanwhile, the other dinosaur was lying on its left side.
And that creature had a jumble of reptilian bones preserved in its abdominal cavity--or at least, in the space where that cavity would’ve been when the dinosaur was still alive.
So thanks to Colbert’s landmark 1989 paper about these two specimens, Coelophysis came to be depicted in TV documentaries, museum exhibits, and books as an opportunist that wasn’t above preying on its own species.
Some writers even claimed the dinosaur ate its own young.
But then, in the early twenty-first century, this sordid little story came into question.
In 2002, paleontologist Robert Gay took a fresh look at the Ghost Ranch fossils.
Remember the one that supposedly had a dinosaur leg in its stomach?
Well, when Gay looked at the specimen, he was taken aback by the proportions.
The leg was big.
The thigh bone alone was more than 13 centimeters long.
To him, it seemed highly doubtful that the full-grown Coelophysis had swallowed such a large object in one piece.
Then a later study of that same specimen cast even more doubt on Colbert’s hypothesis.
If that leg, and the other stomach contents had been swallowed, you’d expect them to be sandwiched between the dinosaur’s left and right ribs, where the guts were.
But, that’s not the case.
The left-side ribs do lie on top of the mixed-up fossils, but the right-side ribs aren’t underneath the fossils.
Instead, they’re pulled backward.
And that’s because paleontologists now think that, after it died, the dinosaur basically … exploded.
It could’ve happened because of the weight of the sediment on top of it, or because of gases that built up in its gut after it died.
But it appears that the abdominal cavity of this Coelophysis ruptured, which makes it hard, if not impossible, to determine what was in its stomach.
So then, what about the other skeleton?
Well, it passed the rib test.
The left and right ribs did actually encase at least some of the bones inside the abdominal cavity.
Plus, this dinosaur had intact gastralia.
Gastrailia are rib-like bones that lined the bellies of many dinosaurs.
In life, they weren’t attached to the rest of the skeleton, so they tend to get lost very easily during the fossilization process.
But since this Coelophysis still had its gastralia and ribs intact, that meant it probably hadn't exploded.
Which is nice!
Because it means the bones found between its ribs must have from the animals it ate.
However, when researchers took a closer look at those bones, they couldn’t find a single fossil that came from another Coelophysis.
Among the few bones that could be identified, a couple closely resembled those of Hesperosuchus, a fast-moving relative of today’s crocodiles that lived alongside the dinosaurs at Ghost Ranch.
So, it seemed like this dinosaur had eaten other reptiles before it died, but there was no evidence that it engaged in cannibalism.
After years of intense study of those two specimens, the reputation of Coelophysis seemed to have been restored -- until the debate took an unexpected, and even more graphic, turn.
While much of that work was going on, another group of paleontologists working with the New Mexico Museum of Natural History and Science was examining a separate block of Coelophysis skeletons from Ghost Ranch.
And they found that one of the adult skeletons in there had a lump of prehistoric poop lodged between the base of its tail and its hip bones.
Normally, fossilized poop samples are called coprolites.
But given its placement, the scientists think this could be a cololite, which is basically a preserved hunk of partly-digested material that was never excreted.
Just ten centimeters long by six centimeters wide and one centimeter thick, this trace fossil was loaded with hundreds of bone fragments.
Bet you didn't think you were going to get that good of a description of a piece of poop today!
Among these, the team discovered wrist and hand bones that looked identical to those seen in juvenile Coelophysis skeletons.
Plus, the scientists later found what appeared to be another totally unexpected and pretty gross trace fossil: fossilized dinosaur vomit.
Fossils of vomit are indeed a thing, although they’re extremely rare, and they’ve been dubbed regurgitalites.
And some of these traces of ancient barf were found in and around the mouth of another adult Coelophysis from Ghost Ranch.
And inside the prehistoric puke, researchers found tiny little teeth that resembled those of a young Coelophysis.
So between the poop and vomit, we may finally have evidence of cannibalism in this dinosaur.
As always, there are those that disagree.
But if it’s true that Coelophysis ate its own kind, it probably wasn’t the only dinosaur that did.
Majungasaurus was a six-meter theropod that terrorized Madagascar in the late Cretaceous Period.
And its bones are sometimes found with bite-marks that perfectly match … its own teeth, both in terms of shape and placement.
Since no other carnivores of its size have been found around it in fossil beds, paleontologists are fairly confident that Majungasaurus regularly fed on members of its own species.
And then there’s our old pal, T. rex.
A 2010 survey of Tyrannosaurus rex fossils concluded that at least four different specimens showed direct evidence of cannibalistic behavior.
The evidence, again, is bite wounds on the bones that match T. rex teeth.
And while there is evidence that some dinosaurs bit each other during combat, there’s no evidence that these bones healed after they were bitten, which suggests that they were chewed on after death.
Now, this leaves us with the big question: Why would dinosaurs like Coelophysis and T. rex eat their own kind, especially when there’s almost no record of avian dinosaurs doing the same thing?
As with cannibalism in other organisms, it could have happened for many reasons.
Perhaps it was a last resort when food was scarce.
Or maybe it helped limit competition, much like modern American alligators are known to eat juveniles of their own species, to eliminate future competitors.
And some animals, from alligators to water bugs, have also been known to engage in cannibalism as a means of population control.
Plus, even if these dinosaurs did eat each other, we still don’t know if they were actively hunting each other or just scavenging on each others’ corpses.
But all told, the decades-long debate about Coelophysis and cannibalism goes to show you that, with solid detective work and a willingness to re-think our assumptions, we can get better at reading the strange clues we find in the fossil record.
And that brings us closer to understanding the ghosts of the prehistoric past--from Ghost