Tyrannosaurus Rex - Hunter Or Scavenger?

[Tyrannoraptor]

I was inspired to make this thread after watching a few documentaries about T. rex (T. rex - Warrior or Wimp and The Valley of T. rex, to name two of them). J. Horner repeatedly stated he wanted to look at the evidence as if he knew nothing about the animal. But I think he came off as being rather biased in this case, he himself stated he doesn't like the animal, so I wanted to know what you people here have to say about this matter.

Personally I think that T. rex was simply an oportunistic animal, taking down its prey when it needed to, but I doubt it would say no to a free meal in the form of an already dead carcass. I can see some of the animal's adaptations being very useful for a scavenger, but so far I think most of the hard evidence suggest predatory behavior.

So, what do you think?

[Jurassic Jim]

Well I am going to come down on the side that it was a capable predator and I agree that it would not pass up someone else's kill. This is a perk of being the apex predator of its time, but the dinosaur was designed to run (3rd metatarsal designed to enable this) and not from smaller predators but to take down prey. Horner has made an agenda of demystifying the most popular dinosaurs, therefore I take pretty much anything he says with a grain of salt. If you look at predators today they typically are a mix of opportunistic and predatory feeders. I just can't imagine it being purely a scavenger, to me it just doesn't even make sense that the largest therapod would fill the niche of scavenger. There are always smaller animals that will fill this environmental niche. Its bone-crushing teeth are certainly different than the slashing teeth of other predators, but those teeth coupled with its massive size seem reasonable. T-rex would not have to had to finesse a kill, but instead just deliver literally devastating bites. Just my opinions as I am no paleontologist.

[mikeymig]

I get a little angry when I hear this all the time on TV. T-rex is just what u said, an opportunist like any good predator. How this even began as an argument is beyond me. T-rex is just like any therapod (and there were more then a few) and they were all scavengers? The only argument the pro scavanger crowd has is that T-rex had small "hands" and couldnt attack live prey. Mother nature never goes overboard and why would she ever make a huge muscle bound bully to eat nothing but dead flesh? Every ecosystem has a balance of predator/prey and during the late Creataceous it was T-rex and Triceratops. END OF STORY!!!!!!!!!!!!!!!!!

[Rockwood]

I think it's likely that the behavior of today's lions is a good analogy. In this case it's the big males that provide brute force when needed but the speed and numbers of smaller members that make them competitive as a species.

[tracer]

the reason t-rex had small forelimbs is because they were in the process of evolving into snakes. specifically, kangaroo hopping snakes.

the giant fangnoidial teeth of t-rex are clearly overkill (pun intended) for eating roadkill, because their morphology isn't very specifically tailored to just cut off a chunk of meat and swallow it. would be like mowing your yard with a um, um <insert ridiculous analogy/metaphor here please [it's early]>.

i figure t-rex picked on those who weren't his size, because reptiles have never been known for their fairness. old, young, infirm, clueless, those-who-can't-dance-well, and yes, the inanimate.

as far as how you fight with little forelimbs - you don't use them much. bite and run, and wait for your victim to bleed out or die of your extreme mouth cooties.

[squali]

the reason t-rex had small forelimbs is because they were in the process of evolving into snakes. specifically, kangaroo hopping snakes.

Oh man that evokes some really scary images. A hopping Riki Tiki Tavi. Remind me not to stop my time machine in that millenium.

[ashcraft]

_{It always made me scratch my head when Dr. Horner said they evolved as scavengers because death rates of other wpecies were so high. If death rates were high, I have to assume they were then higher then birth rates, so extinction would be the result in a very few generations. Evolving into a niche where the food source is becoming extinct, is generally not a good idea for long term survival.}

_{Brent Ashcraft}

Edited December 5, 2011 by ashcraft

[bear-dog]

These arguments are almost as old as the beast themselves.I personally think the T-Rex was a fierce predator that also lived by the 30 second rule if someone else dropped their lunch.

[Sinopaleus]

i think mr. horner is biased. he even suggested that triceratops was the juvenile form of a torosaurus. however, i do agree with the nanotyrannus=baby t-rex theory. eg, 17 teeth found in nano, 16 &15 found in juvenile t-rex, 14-13 teeth found in young adults, 12 in adults

t-rex didnt evolve such a huge head to nibble on scraps of rotting meat. the arms in fact showed signs of usage, perhaps in mating or for carrying fresh kill to nests to feed young. idk, but that's what i heard from a trustworthy documentary of t-rex.

[Tyrannoraptor]

the reason t-rex had small forelimbs is because they were in the process of evolving into snakes. specifically, kangaroo hopping snakes.

the giant fangnoidial teeth of t-rex are clearly overkill (pun intended) for eating roadkill, because their morphology isn't very specifically tailored to just cut off a chunk of meat and swallow it. would be like mowing your yard with a um, um <insert ridiculous analogy/metaphor here please [it's early]>.

i figure t-rex picked on those who weren't his size, because reptiles have never been known for their fairness. old, young, infirm, clueless, those-who-can't-dance-well, and yes, the inanimate.

as far as how you fight with little forelimbs - you don't use them much. bite and run, and wait for your victim to bleed out or die of your extreme mouth cooties.

I think mowing your yard with a combine harvester would be a good analogy...

Anyway, in my opinion Horner's arguments for scavenger theory don't hold up (I'm gonna try and break them up into several points):

1. Bite marks to that Triceratops sacrum could only have been done post-mortem, as they weren't accessible while the animal was still alive - true, but this proves exactly nothing and doesn't support the scavenger theory at all, since T. rex could still kill the animal and those bite marks were just the result of feeding later. This is a really weak argument.

2. Small arms. Well, neither birds nor crocodiles use their front limbs to stabilize their prey, jaws do all the work. Besides, despite being small those T. rex's arms were quite powerful. Maybe their smaller size was simply an adaptation so that T. rex could carry that massive head and still be able to stay balanced on two legs?

3. Bone crushing jaws and teeth werent used for slicing meat, but rather for crushing bones and extracting bone marrow - please don't tell me this wouldn't be useful to a predator too, especially when its prey was so well protected against attacks. Bone crushing bite could inflict some really serious wounds, perhaps increasing the probability of a successful kill. Comparing T. rex to the hyenas doesn't work in support of scavenger theory either, since viewing hyenas as scavengers is now known to be wrong, too (they actually kill over 90% of their own food).

4. Large olfactory region of the brain indicates excellent sense of smell, which was excellent for smelling carcasses from the long distances. This is probably the best of Horner's arguments in support of the scavenger theory, but this is an adaptation that could be very useful for hunting, too.

5. Tyrannosaurus rex's brain had small visual center, so its eyesight must have been poor - well, what about its stereoscopic vision, which was slightly better than that of modern hawks, and was the best among large predatory dinosaurs? Isn't this a good sign that T. rex evolved this because it was very helpful when hunting and planning attacks? J. Horner completely ignores this second part.

I think that looking at the evidence in an unbiased way could lead to one simple conclusion - yes, Tyrannosaurus rex could deffinitely hunt. Perhaps the most firm evidence for this are the healed bite marks on a Triceratops's horn and frill, and a healed bite mark on the tail of a hadrosaur, both of which fit T. rex's teeth perfectly. No matter how I look at it (and I even looked at the scavenger theory as plausible), the evidence points to T. rex being a predator, probably an oportunistic one.

[Missourian]

According to Jurassic Park, T. rex likes lawyers and jeep sunroofs, so I guess it can be both predator and scavenger.

[siteseer]

I have seen those shows too and would have to agree with Horner to a point. Of course, a larger predator will run off a smaller one for a decent meal and take down an already injured or sick animal but I don't think T. rex was running down its prey. Think of the weight of an adult. I've heard it could weigh about 4-6 tons and unlike much smaller lions, tigers, and bears, T. rex traveled on only its hind legs. If running puts four times the weight on your limbs as walking, that's an incredible amount of stress to put on the knees, ankles, and toes - probably to the breaking point at any one of those areas. One bad step on uneven ground could lead to a devastating injury. Horner thought that T. rex was good walker covering a lot of ground with a long stride. I'm not saying it couldn't run but it carried more of a risk and was less energy-efficient for such a large animal.

It's hard to make comparisons. T. rex was different than other predators and other theropods - unusual for the size (maybe three other genera reached it) and unique for its teeth (as noted by others, they were more bone-crushers than meat-slicers). It could crunch bones no other land carnivore in geologic time could have. It was an adaptation useful for its time as dinosaurs were apparently less diverse at the time/place of T. rex (roughly the last five million years of the Cretaceous). It could eat what no other predators could of a large dinosaur carcass and bones are nutritious if you can bust them up.

I think this topic has been discussed before (maybe a year or two ago) so it might be worth a search of the forum itself for those interested in this thread.

Well I am going to come down on the side that it was a capable predator and I agree that it would not pass up someone else's kill. This is a perk of being the apex predator of its time, but the dinosaur was designed to run (3rd metatarsal designed to enable this) and not from smaller predators but to take down prey. Horner has made an agenda of demystifying the most popular dinosaurs, therefore I take pretty much anything he says with a grain of salt. If you look at predators today they typically are a mix of opportunistic and predatory feeders. I just can't imagine it being purely a scavenger, to me it just doesn't even make sense that the largest therapod would fill the niche of scavenger. There are always smaller animals that will fill this environmental niche. Its bone-crushing teeth are certainly different than the slashing teeth of other predators, but those teeth coupled with its massive size seem reasonable. T-rex would not have to had to finesse a kill, but instead just deliver literally devastating bites. Just my opinions as I am no paleontologist.

[Boesse]

I think quite a few people get so offended by the notion of what Jack Horner says that their favorite dinosaur was doing or not, they forget about the fact that paleontology is a science, a few steps above informed speculation. Science depends upon data, evidence, and skepticism: something that Jack has talked about before at length is that we don't really have any direct evidence of bona fide predation in the fossil record (at least with the dinosaur fossil record, for example). Say what you want about likelihood of predation - but gut contents and tooth marks can just as easily be argued away as signs of scavenging. Healed bite marks, while by default require the injury to be made during life, can always be misdiagnosed (i.e. some other injury or disease) or if truly made by a predator, could have been made in a case of aggression not related to feeding (e.g. territoriality).

That all being said, there is one additional piece of relatively damning evidence published within the last few years by Wolff et al. (2009) http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007288, is that T. rex specimens are commonly pathologic, and the pathology appears to be identical to that caused by an oral disease in modern birds. As it turns out, most of the species with this disease are carrion eaters, such as vultures and condors.

While all of this informed (or uninformed) speculation can be fun and seem important, the truth is that we don't know given the available evidence. We also have to accept the possibility that we can't know. Lastly, we need to be able to divorce ourselves from hypotheses and ideas we like or find more comforting.

[Tyrannoraptor]

Boesse and siteseer - now these are stronger arguments for the scavenger theory. I wasn't as much offended by what Horner suggested (well, maybe at first, but I got over it in time... You know, didn't want to have my childhood ruined and all ), I rather thought that his most popular arguments in support of his theory are weak, and some could hardly be considered arguments at all.

I didn't think T. rex would run down its prey in the same way a cheetah does, as I doubt it could run for a very long time due to its massive weight. I was thinking more along the lines of it being an ambush predator, trying to get as close to its victim as it could before attacking. And perhaps the largest animals didn't even need to bring their food down on their own, they could have stalked the younger Tyrannosaurs and steal their kills, or perhaps even hunt in packs, but these are all just speculations.

But I have no doubt at all that T. rex would also be scavenging, and being able to travel long distances more efficiently would make sense. Weren't dinosaur species numbers dropping for a few million years before their extinction? Perhaps the food was getting more scarce, so T. rex would indeed have to travel long distances to find a meal. And in this case its excellent sense of smell would help a lot - finding a rotting carcass was still better than finding no food at all.

And it is possible that we might never know, yes.

Edit: I've read the article in the link. They seem to suggest that there could be various reasons for the disease to occur, such as head biting, which could spread the infection among individuals, and that eating infected food can not be ruled out. I've also looked up about the disease itself a bit (could do some more research, but I don't have much time on my hands right now), but from what I've found it looks like eagles and other modern raptor birds can be infected too, so it doesn't really matter if the animal is a pure scavenger or a predator, because carrions could be a substantial source of food for predators, too.

Edited December 7, 2011 by Tyrannoraptor

[tracer]

as far as cheetahs, everybody knows they eat cheetos.

i find it incomprehensible that t-rex wouldn't have been both an opportunistic scavenger and a predator of whatever in it's considerably astute judgement (i say this because they're always remarkably talented actors in movies) it could manage to render immobile and edible.

on the venn diagram of survival, i see no reason for a lizard the size of waco (got tired of saying dallas) would cut out a substantial subset of the available vittles.

[ashcraft]

Show me one other animal of that size/ecological niche that is a pure scavenger. There isn't. The closest would be wolverines or Tasmanian Devils. Both of which will take live prey.

For such a feeding strategy to evolve, there would have had to have been large numbers of edible carcasses becoming available through death from other causes then predating (freezing to death in the case of the wolverine, which is a 50 pound weasel). The sheer size of t-rex and the amount of caloric intake would have been substantial, what kind of force would have been causing such killing? How long must have it been going on for an organism to become adapted to that life style? Wouldn't a smaller size have been more advantageuos? Vultures are largeish because of need for soaring wings, and they cannot break up bone. You would think that if such a niche was easily filled, that something would have done a similar "job" at the end of the ice age, when the megafauna were going extinct.

It is all speculation of course, but heeding to Occam's razor, there are many more problems associated with being a scavenger then being a predator.

I think Horner did what he wanted, created a furor, and made money off of it.

Brent Ashcraft

[Boesse]

I forgot to mention that there are plenty of folks who dislike Horner, which is fine. Most paleontologists don't really make a lot of money, Horner included, so I have no idea why you'd say that. Think about how much research was spurred by people who disagreed with Horner's hypothesis - disagreement in science is healthy; it means the field isn't stagnating.

A point of clarification: obviously I think the opportunistic idea is the most reasonable. However, I believe that thinking like the Devil's Advocate is one of the most valuable methods of being skeptical and generating alternative hypotheses and ways to test weakly constructed hypotheses, arguments, or assumptions. And the simple fact remains that there isn't any "real" positive evidence that T. rex was a predator.

[Diplotomodon]

I suppose it would be amusing to mention this....

Last time I went to the Academy of Natural Sciences I heard that Jack Horner was there in May. Simply put, he got pummeled by the audience about this very subject. After a while it seems he admitted that T. rex was probably not a strict scavenger and opportunistic instead. Not sure about the validity of this story because I wasn't there and only heard it from the other speakers, but it sounded like it was fun to watch.

Now we just have to wait and see what happens to the Triceratops/Torosaurus fiasco....

[piranha]

False facts are highly injurious to the progress of science, for they often endure long; but false views, if supported by some evidence, do little harm, for every one takes a salutary pleasure in proving their falseness.

- Charles Darwin

[Tyrannoraptor]

I forgot to mention that there are plenty of folks who dislike Horner, which is fine. Most paleontologists don't really make a lot of money, Horner included, so I have no idea why you'd say that. Think about how much research was spurred by people who disagreed with Horner's hypothesis - disagreement in science is healthy; it means the field isn't stagnating.

A point of clarification: obviously I think the opportunistic idea is the most reasonable. However, I believe that thinking like the Devil's Advocate is one of the most valuable methods of being skeptical and generating alternative hypotheses and ways to test weakly constructed hypotheses, arguments, or assumptions. And the simple fact remains that there isn't any "real" positive evidence that T. rex was a predator.

I get where you're coming from. I know a lot of people hate Jack Horner, and I'll admit it, I hated him for a while, too. But then it got me thinking, and I completely agree with you - his claims/theories spurred a lot of research in the field, and as a result we now know a lot more about Tyrannosaurus rex than before. Skepticism isn't as bad as some might think.

While there isn't any proof positive evidence for T. rex being a predator or scavenger (actually I don't think there's any real proof about any other giant theropod dinosaur being a predator either) one might still assume that the ancient ecosystems worked in the same ways as modern ones do - large predators for the big game prey, smaller predators for smaller to medium sized prey (if hunting in packs of course). I know, it's just a simplified explanation.

Oh, and one more thought that occured to me - the animals with the strongest bite that are living today are the crocodiles and aligators, and they are predators. I imagine they are quite capable of crushing bones, too.

Anyway, I agree with your post.

I suppose it would be amusing to mention this....

Last time I went to the Academy of Natural Sciences I heard that Jack Horner was there in May. Simply put, he got pummeled by the audience about this very subject. After a while it seems he admitted that T. rex was probably not a strict scavenger and opportunistic instead. Not sure about the validity of this story because I wasn't there and only heard it from the other speakers, but it sounded like it was fun to watch.

Now we just have to wait and see what happens to the Triceratops/Torosaurus fiasco....

Oh, poor guy. He really gets a lot of **** about this, doesn't he? I'm not sure if I'd laugh if i was there or not. I simply couldn't stay serious when I heard his argument why the Triceratops couldn't use his horns for defense (he said that if a Triceratops would slam into a T. rex with its horns, the T. rex would fall down right on that Trike's head, killing it too). But I don't know, I might just have felt sorry for him there. He didn't mean to do anything bad after all.

Has that Triceratops/Torosaurus theory been disproven then? Funny, I found out about it not a long time ago and was just beginning to adjust to the idea and then this happens...

[Auspex]

T-Rex was equipped to eat just about anything it wanted to, and I see it as a supremely adapted predator (who would never turn down leftovers either).

[Missourian]

Regarding the controversy with Horner, the short of it is:

"Don't mess with everyone's favorite dinosaur!"

[Vordigern]

I believe T-rex ,like myself ,would never pass up on a free meal but I believe the majority of his diet came from his abitities as a hunter, not as a scavenger

[ashcraft]

I forgot to mention that there are plenty of folks who dislike Horner, which is fine. Most paleontologists don't really make a lot of money, Horner included, so I have no idea why you'd say that.

There were a number of specials done on his hypothesis, on which he was the consultant. I don't know what that pays, but I am sure it is better than what I got for the night class that I just finished to make ends meet. I suspect he also made a number of speaking engagements on the subject, and I doubt that he did them for free. Money is everywhere, and tempers everything, nothing is pure.

I have never met Dr. Horner, probably wouldn't recognize him in person. What I have seen of him hasn't made a good first impression. But then again, I ususally do make a good first impression, its usually the second or third meeting that does me in.

Brent Ashcraft

[siteseer]

I've been meaning to get back to this thread...

Think of the largest birds. What are they? Condors. Condors are scavengers. I don't know if the bird-dinosaur lineage has any relevance there - probably not. However, we do have to look at other giant theropods like Carcharodontosaurus and Torvosaurus. Judging by their teeth, they were processing different food than Tyrannosaurus. Was it because T. rex was attacking a greater diversity of armored prey (ceratopsians and ankylosaurs)? Was it because there was opportunity for a mega-scavenger at that particular point in geologic time. It could be that young adult tyrannosaurs were primarily predators but mature adults became too large to run down or ambush prey on a regular basis but they could consume parts of a carcass no other animal in earth history could have accessed. With a great sense of smell and a long walking stride an older Tyrannosaurus was more energy-efficient following its nose to less-edible carcasses and was big enough to scare off smaller predators from fresher kills.

When you ask to show you another scavenger of the same size in today's world that assumes the world was the same 65-70 million years ago and it wasn't. The continents had different coastlines and were in different positions though you could distinguish the broad outlines. The atmosphere was about the same though it was a time of high-level volcanic activity we would not have experience with. World climates and ocean currents were very different. It was a different jungle of parasites, microorganisms, and diseases.

Dinosaurs were not mammals. They had a physiology paleontologists are still trying to figure out the hard way. Today, and through much of the Cenozoic a mammal the size of an elephant has been among the largest mammals. During the Cretaceous, an elephant would have been a medium-sized land vertebrate with many others double or triple the weight. For some reason mammals have never been able to super-size to dinosaur levels even after the dinosaurs were long-gone.

I'm throwing thoughts out there but mainly saying that different points in geologic time were separate worlds. Sixty-five million years ago is not much time in terms of earth's history but enough of a duration in the history of life for a lot to change. Organisms have lifestyles today that may be unique. There's an eagle in South America that cracks and breaks up large mammal bones by picking them up and dropping them from a great height. Organisms in the past were apparently at least as weird in their own way in their own time.

Show me one other animal of that size/ecological niche that is a pure scavenger. There isn't. The closest would be wolverines or Tasmanian Devils. Both of which will take live prey.

For such a feeding strategy to evolve, there would have had to have been large numbers of edible carcasses becoming available through death from other causes then predating (freezing to death in the case of the wolverine, which is a 50 pound weasel). The sheer size of t-rex and the amount of caloric intake would have been substantial, what kind of force would have been causing such killing? How long must have it been going on for an organism to become adapted to that life style? Wouldn't a smaller size have been more advantageuos? Vultures are largeish because of need for soaring wings, and they cannot break up bone. You would think that if such a niche was easily filled, that something would have done a similar "job" at the end of the ice age, when the megafauna were going extinct.

It is all speculation of course, but heeding to Occam's razor, there are many more problems associated with being a scavenger then being a predator.

I think Horner did what he wanted, created a furor, and made money off of it.

Brent Ashcraft