National Geographic News
New research confirms that T-rex hunted hadrosaurs (file illustration).

There is new evidence that the T. rex hunted hadrosaurs such as the Anatosaurus seen in this illustration.

Illustration by Roy Andersen, National Geographic

Ker Than

for National Geographic

Published July 15, 2013

A fossil tooth found buried inside the healed tailbones of a duckbill dinosaur suggests the animal survived a close encounter with a Tyrannosaurus rex about 65 million years ago, according to a new study.

Scientists say the embedded tooth, discovered in the Hell Creek Formation in Montana, is the first conclusive proof that T. rex was not just a scavenger, but also a predator that hunted and killed prey. (Related: "Scarred Duckbill Dinosaur Escaped T. Rex Attack.")

"It's not just a smoking gun—we've actually found the bullet," said study co-author Peter Larson, a paleontologist at the Black Hills Institute of Geological Research in South Dakota.

But not everyone agrees. Jack Horner, a paleontologist at Montana State University who has long argued that T. rex was incapable of hunting healthy adult prey, remains unconvinced.

"It's one data point, and that's the least amount of data you can have," said Horner, who was not involved in the research.

Scavenger or Killer?

A long-running debate about T. rex concerns whether it was an "obligate scavenger"—surviving solely on the flesh of dead animals—or whether it was an active predator that hunted prey.

The fossil evidence has been inconclusive on this matter. That's because while dinosaur bones and even fossilized skin have been found with tooth marks linked to T. rex, it's impossible to conclusively prove whether an animal was alive or dead when it was bitten.

"If a T. rex bit a bone of an animal that was already dead, that mark looks identical to what would be made on an animal that it just killed," said lead author Robert DePalma, a paleontologist at Florida's Palm Beach Museum of Natural History.

So instead of relying solely on bite marks, some scientists have tried to determine T. rex's feeding style by analyzing its physical and sensory attributes.

Paleontologists such as Horner have concluded that T. rex was not only too slow to chase down prey, its arms were too puny and its eyesight was too poor for it to successfully attack or chase down a healthy adult animal. At best, T. rex could have chased down lame, young, or weak animals, but otherwise it lived on  carrion, Horner said.

"My argument has always been that T. rex is [an opportunist] like a hyena," he added.

End of Debate?

But DePalma and his team say the T. rex tooth, which measures about 1.5 inches (3.75 centimeters) long, solidly refutes that idea. "It puts the debate to rest," DePalma said.

The fact that the bitten duckbill dinosaur—also known as a hadrosaur—managed to escape suggests it was more than a match for its pursuer, he argued, and thus unlikely to have been young, weak, or handicapped.

"We can tell [the T. rex] bit a living animal because the two vertebrae were infected and then fused together," DePalma said. "So it's unmistakable that the tooth was in there before the animal died."

Also, the location of the injury—near the tip of the duckbill's tail—suggests T. rex was pursuing the animal when it was bitten. "The fact that the injury is on the hindquarters of the animal is actually not surprising," DePalma said. "If you examine Kalahari lions, for example, they will attack the hindquarters of their victims to immobilize them and then they'll go in for the kill."

To identify the animal the tooth belonged to, DePalma and his team extracted it from the tailbones and made detailed measurements. "The morphology is unmistakable for T. rex," DePalma said. "It could not be mistaken for any other carnivorous species."

The tooth's size and shape indicates it came from the T. rex's lower jaw, and its loss likely did not affect the creature in any significant way.

"Like sharks and lizards, T. rexes kept replacing their teeth throughout their entire lives," DePalma explained.

"That tooth would have been replaced in a matter of months, and it would have been sharper than ever." (Learn the latest on what scientists know about T. rex.)

How It Went Down

Using modern predators as a model, DePalma and his team have imagined a number of ways the failed hunt might have happened.

One possible scenario, DePalma said, is that the T. rex was prowling around a watering hole or food source where duckbills gathered, or perhaps it was hiding in nearby foliage and attempted to ambush the animals.

Hell Creek at the end of the Cretaceous era was not the dry, rocky desert it is today. It was a temperate forest environment crisscrossed by rivers filled with crocodiles and turtles.

The T. rex "would have probably gone after the closest hadrosaur it could get its mouth on, and in this case it proved too much of a match for it," DePalma said.

Larson, on the other hand, imagines a small pack of T. rexes joining forces to take down the duckbill. Multiple T. rex individuals have been found buried together, which suggests that they could have lived, and possibly hunted, together.

"A scenario might be a family of two or three related individuals that hunted together," he said. "One animal would distract the prey or perhaps send a herd of duckbills scattering, while the other Tyrannosaurs would lie in wait and eventually take up the chase for the weaker individual."

Had the T. rex managed to run down its prey, its next step would have been to use its weight to muscle the duckbill down to the ground.

It would have then "grabbed on with its arms in order to move its head forward to try to either clamp the muzzle to suffocate it or try to tear open the throat," Larson said.

No Evidence

Horner said such imagined scenarios are idle speculation not supported by the evidence.

This fossil only "shows that a T. rex bit a live duckbill dinosaur. There's no evidence that it was chasing it," he said.

Horner offered his own speculative scenario for what might have happened: "A T. rex could have walked up to a sleeping duckbill dinosaur and bit it, realized it was alive, and then backed away," he said. "That's just as plausible as saying that it's chasing it because there's no evidence for either one."

In addition to ending the debate about T. rex's predatory behavior, DePalma thinks the tailbones will help paleontologists reconstruct the ecology of the Hell Creek Formation 65 million years ago.

"When you have a giant carnivore that composes a significant portion of the ecosystem, identifying its role as either a predator or a scavenger is going to have significant implications for paleoecological reconstructions," DePalma said.

The research is detailed in this week's issue of the Proceedings of the National Academy of Sciences.

24 comments
andy red
andy red

T-Rex and survived than that means the T-Rex was obviously in pursuit of it. If a T-Rex was a scavenger like a Hyena then it wouldn't have bothered with trying to eat a live prey

http://www.royalegoal.com/ 

Jesse Baker
Jesse Baker

"Horner said such imagined scenarios are idle speculation."  I agree with the paleontologist.  We just don't know.  We weren't there, and they didn't leave too many behavioral traces other than the bite marks and footprints, and that embedded lost tooth.  Pack hunting?  Did T. rex have enough brains to support this?  No modern birds or reptiles exhibit truly cooperative hunting strategies.


T. rex was basically a huge mouth on two walking legs.  I guess that's a good way of getting down to the business of eating.


Another interesting question is top dino size--much larger than seen with contemporary animals.  How did the ecosystem's primary plant productivity support these huge beasts, especially if they were running around in herds and packs as now-popular imagination has them doing?  It seems to me that a T. rex would have needed a territory as big as Connecticut to get enough calories.

Harry W Smith
Harry W Smith

T-Rex hunted like the  predators  today.  It hunted to feed its young. It would have never hunted  for humans, if it were alive today. It is human that kills humans. 

grissle productions
grissle productions

is it possible that T-rex hopped along like a kangaroo ? with its huge back legs and tiny arms and a big tail for balance its not unlike a modern kangaroo,is it possible ?could it be the worlds first hopping predator/scavenger ? its just a thought.*tic*

Sandeep Banerjee
Sandeep Banerjee

Wait, I don't get it. T-Rex was supposed to be the fiercest predator of them all, so why would it have needed to scavenge?

Eduardo Cianelli
Eduardo Cianelli

Truth is that T.rex, used drones to hunt for their prey..scanning the terrain, looking for victims....

Gary Dawson
Gary Dawson

The comment on one data point is ludicrous, especially that his pet theory is supported by no data whatsoever, just pure speculation.  Also absurd is that a paleontologist would say one point of data is meaningless when we have entire species described by no more than one vertebrae. That is like saying these species did not exist because there is not enough data points.

Nancy Greene
Nancy Greene

It has been proven that hyenas also hunt, so that point is no longer valid.

Richard Alexander
Richard Alexander

It's odd that this tooth leads to the only reference to T. rex as a scavenger that I have heard outside of Creationist literature.

Mohammad Abdullah
Mohammad Abdullah

What? Isn't Horner eventually admitted that T.rex is both a hunter and scavenger? He is very confusing.

James Donnaught
James Donnaught

It's hard to imagine a T. Rex "sneaking up" on anything - even a sleeping dino.  And why would it be sneaky if was looking for carrion?  And then, coming across what it thinks is dead, why bite into the tail?  That's not where the meat is.  

Horner is grasping at straws, rather than objectively evaluating the evidence.  That's bad science, Jack!

N. D
N. D

It's a bit presumptuous to characterise an entire species based on a single tooth isn't it? 

Kathy Harris
Kathy Harris

The notion that a T-rex's short arms make it unable to be categorized as a predator is not supported by other examples in living species. I mean, snakes and sharks have no arms and they hunt live prey.

Grey Dennis
Grey Dennis

I hate how this so-called expert on predatory behavior (Jack Horner) portrays many inaccuracies. 1. Hyenas are not obligate scavengers, and in fact are the most prominent predators in some areas, way more than lions in those areas. 2. Why would a scavenger, or rather any carnivore, attack the tail instead of any other part of a herbivore's body? The tail is one of the boniest parts of a body, especially the tip. It is way more likely the bite was a futile attempt to grab an already basically escaped prey item. 3. Tyrannosaurus Rex had a very developed sense of smell. Pretty sure it would be able to tell whether a dinosaur was dead or not. Bodies begin to rot pretty quickly and that makes them give off specific scents that a scavenger would have to know how to detect.

William S.
William S.

If the herbivore Dinosaur had an encounter with the T-Rex and survived than that means the T-Rex was obviously in pursuit of it. If a T-Rex was a scavenger like a Hyena then it wouldn't have bothered with trying to eat a live prey.   

J. J.
J. J.

@grissle productions It was once believed that theropods (carnivorous dinos) did move like that. In Arthur Conan Doyle's novel The Lost World, the allosaur/megalosaur moves about by hopping... 

But seriously, no way an animal as heavy as T-Rex moved like that. I do remember reading about some trackways of a smaller theropod- I think it was Megapnosaurus- that seemed to have hopped about like a bird, but I'm not sure if that is still a valid theory, and most dinosaur trackways show that plain walking was how they moved about most of the time.

J. J.
J. J.

@Sandeep Banerjee Even the fiercest predators today- think tiger, lion, great white shark, crocodile etc- scavenge whenever they have the chance. Much easier and less risky than stalking, chasing and wrestling your own prey. This whole debate is really pointless- there's no actual reason to believe T. rex was any different from modern day predators in this regard.

Nick Mitsialis
Nick Mitsialis

@Gary Dawson Well, Horner has 'sort of' backtracked on his comments RE: the Rex. He says it's to encourage more critical thought on the subject.

Nick Mitsialis
Nick Mitsialis

@James Donnaught I don't know, James. It's assumed duckbills & ceratopsians travel in large herds & that the terrain the Rex lived in was heavily forested & swampy. I imagine (yes, I am speculating) that a herd of edmontosaurs or triceratops would make a lot of noise & smell as they munched, vocalized, broke brush, knocked down trees & pooped. A Rex could lurk or lie in wait around the edges of a herd for an animal to get 'careless'.  Or lie in wait at migratory choke points, like river crossings; or it could wait for the rutting season--a bunch of hormonally distracted & possibly injured male ceratopsians might be easier to sneak up on--heck it works for great white sharks & elephant seals.

Alex Isidoridy
Alex Isidoridy

@Nuwan D I totally agree. There is modern evidence that, at times, vultures are know to hunt living prey.

This fossil only.. "shows that a T. rex bit a live duckbill dinosaur. There's no evidence that it was chasing it," he said.

Exactly. One fossil does not prove a thing. If it is from 65 million years ago, the world could have been "ending" and the "scavenger" might have just failed at "hunting".

Russ Nash
Russ Nash

@Grey Dennis I agree. Hyenas certainly do hunt, and quite well. Usually at night. I'd guess that a hunting T Rex with a developed sense of smell would pretty certainly hunt upwind - although as group hunters who knows what plans they were capable of? The small arms I consider irrelevant to the question. They were still pretty strong but with a head, neck and feet like that, not so important - just as they weren't in terror birds for example. As you say of Hyenas "not obligate scavengers".

William Dasilva
William Dasilva

@Grey Dennis  I agree, Why would the T rex choose to bite the tip of a sleeping dinosaurs tail? It makes no sense. if it thinks its dead it would go for where the meat is. also good point about the Hyenas. in fact it seems Hyenas are more likely to be scavengers if bigger predators are around like lions. as for the T rex its WAS the lion of its time. it had the thickest most muscular skull around and jaws made to destroy. It jus sounds to me like Horner just wants to defend his theory even if it isn't logical.

Nick Mitsialis
Nick Mitsialis

@J. J. @Sandeep Banerjee Well, what you say about predators IS true, but if I understand things correctly, there aren't many other predators to clean up after or bully from their kill except other Tyrannosaurids.

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