Was Tyrannosaurus a predator or scavenger?

[GeoffP]

Tired of thumping on people, I turn my weary eyes to science. (I understand this forum has something to do with the field.)

I've been watching a bit of Discovery and found something that boils my blood a bit (although I promise not to froth): the supposition that tyrannosaurs were scavengers. The evidence appears largely to be based on the size of their nasal cavities and their stumpy forelimbs. Yet this doesn't strike me as convincing. Any budding paleontologists out there (or people just wish they were, like me) want to take a stab at it?

I've included a range of options above: I wanted to feel out sentiment for the "ultimate killing machine" 100% predator perspective and the slow, complete scavenger perspective. Possibly opinions will occupy a normal distribution.

 

[S.A.M.]

Tired of thumping on people, I turn my weary eyes to science. (I understand this forum has something to do with the field.)

I've been watching a bit of Discovery and found something that boils my blood a bit (although I promise not to froth): the supposition that tyrannosaurs were scavengers. The evidence appears largely to be based on the size of their nasal cavities and their stumpy forelimbs. Yet this doesn't strike me as convincing. Any budding paleontologists out there (or people just wish they were, like me) want to take a stab at it?

I've included a range of options above: I wanted to feel out sentiment for the "ultimate killing machine" 100% predator perspective and the slow, complete scavenger perspective. Possibly opinions will occupy a normal distribution.

The bite force of T. Rex was studied by Meers

http://www.informaworld.com/smpp/content?content=10.1080/0891296021000050755

The feeding behavior of the theropod dinosaur Tyrannosaurus rex is investigated through analysis of two variables that are critical to successful predation, bite force and prey body mass, as they scale with the size of the predator. These size-related variables have important deterministic effects on the predator's feeding strategy, through their effects on lethal capacity and choice of prey. Bite force data compiled for extant predators (crocodylians, carnivorans, chelonians and squamates) are used to establish a relationship between bite force and body mass among extant predators. These data are used to estimate the maximum potential bite force of T. rex, which is between about 183,000 and 235,000 N for a bilateral bite. The relationship between maximum prey body mass and predator body mass among the same living vertebrates is used to infer the likely maximum size of prey taken by T. rex in the Late Cretaceous. This makes it possible to arrive at a more rigorous assessment of the role of T. rex as an active predator and/or scavenger than has hitherto been possible. The results of this analysis show that adult Triceratops horridus fall well within the size range of potential prey that are predicted to be available to a solitary, predaceous T. rex. This analysis establishes boundary conditions for possible predator/prey relationships among other dinosaurs, as well as between these two taxa.

But since the maximum bite force in living vertebrates is found in hyenas (successful predators and scavengers) it does not really resolve the issue.

Still, there are some indicators of predation:

... solitary predators are highly unlikely to take prey items that are much larger than themselves, while cooperative (or pack) hunters may take much larger animals. For example, a rare Tiger may kill even an adult Guar (roughly 500% greater body mass), but it's comparatively common for a pack of lions to kill a giraffe (roughly 700% greater body mass than a typical lion).

As it turns out, the average relationship between predator and largest prey body mass is fairly tight statistically (see Meers, 2003). In simple terms, solitary predators largest prey items average 136% of the predator's mass. Pair-bonded cooperative hunters average a bit larger maximum prey size (190%), while pack hunters average maximum prey size is a whopping 542% of the mass of an individual predator!

For dinosaurs like T. rex, this means that as long as their hypothesized prey item didn't exceed about 136% of their own body mass, it's reasonable to conclude that T. rex may have been able of killing that potential prey. As it turns out, in the Late Cretaceous of North America, the largest potential prey for T. rex was Triceratops horridus, the famous three-horned dinosaur every little kid loves. With a body mass very similar to estimates for T. rex, it seems likely that T. rex would have been capable of killing even adult Triceratops .

 

[Anti-Flag]

Well there's a number of factors considered as to why T-rex would be a scavenger. The forelimbs and their muscles being unable to grab flesh is probably not such a big deal so I'm surprised they focused on that. What they should have mentioned is the latest extrapolation of the overall muscle mass and balance issues. It's top speed wasn't all that great and as I recall it has serious balance issues at speed, especially with regards to it's head, quite the lumbering dino so not really hunter material by a long way.
That being said it could have preyed on small or slow creatures, but probably would just take what it can get, and of course could easily bully smaller dino's off of their kill. It's teeth could crush bone, which would fit a scavenger profile.
What should be mentioned is that in regards to SAMs info T-rex fossils have been recovered with damage consistent of that of being involved in fights with herbivores and also herbivore fossils have been found with T-rex bite wounds that have healed(obviously indicating the prey wasn't being scavenged).
It's likely they were both - primarily scavengers but were fully prepared to fight for a meal if hungry enough or the odds were favourable.

 

[Enmos]

Well there's a number of factors considered as to why T-rex would be a scavenger. The forelimbs and their muscles being unable to grab flesh is probably not such a big deal so I'm surprised they focused on that. What they should have mentioned is the latest extrapolation of the overall muscle mass and balance issues. It's top speed wasn't all that great and as I recall it has serious balance issues at speed, especially with regards to it's head, quite the lumbering dino so not really hunter material by a long way.
That being said it could have preyed on small or slow creatures, but probably would just take what it can get, and of course could easily bully smaller dino's off of their kill. It's teeth could crush bone, which would fit a scavenger profile.
What should be mentioned is that in regards to SAMs info T-rex fossils have been recovered with damage consistent of that of being involved in fights with herbivores and also herbivore fossils have been found with T-rex bite wounds that have healed(obviously indicating the prey wasn't being scavenged).
It's likely they were both - primarily scavengers but were fully prepared to fight for a meal if hungry enough or the odds were favourable.

Maybe they evolved from smaller more ballanced predators towards larger (mostly) scavengers. Although they could easily have been ambush predators, i mean one bite and youre history..

 

[Anti-Flag]

Maybe they evolved from smaller more ballanced predators towards larger (mostly) scavengers.

I believe that's correct. The oldest dinosaurs were obviously not huge and would have gradually evolved to be larger in conjunction with the increasing availability of food and in the case of carnivores the size of the prey.
Much like the sauropods got larger.
It's likely T-rex's ancestors were better hunters and rarely scavenged and over the course of evolution scavenging became more frequent on some branches of the tree.

Although they could easily have been ambush predators, i mean one bite and youre history..

They probably would have to have been, as I said I don't believe they're well equipped for running, too slow, and it's highly unlikely to have been efficient enough to sustain a chase.
It would have picked off slow animals along with the weak or injured.

 

[Pandaemoni]

I've been watching a bit of Discovery and found something that boils my blood a bit (although I promise not to froth): the supposition that tyrannosaurs were scavengers.

This is one of those issues that leaves me scratching my head. Why would anyone, even an expert, have such an emotional reaction to such an hypothesis? I'm sure there are very plausible just-so stories on both sides, placing T-Rex as a hunter or as a scavenger. If the experts are presently marshaling evidence on both sides of the debate, why should I (or anyone) be opposed to simply admitting "We don't know whether and to what extent the T-Rex was a scavenger or a predator"?

Perhaps I am not sufficiently emotionally invested in dinosaurs, but if the Experts are debating the question, then it seems like that should be good enough for me until some more definitive evidence is found and shared.

 

[Fugu-dono]

Lions and Hyeanas can be both predator and hunter. Why can't T-Rex be the same? T-Rex was likely the bully of it's time.

 

[GeoffP]

I think tyrannosaurs were pretty quick, actually: not as quick as in Jurassic Park or something but fairly fast - 25 kph? I also don't agree with the assessment by some 'experts' that the small forearms precluded predation: diatrymas and the whole "terror bird" family were top predators for - what? 10 million years? - and didn't have functional forearms either. Neither does any predatory flying bird of the modern era, but they still occupy a position as top predator in the absence of mammalian ones. I think the biome-wide existence of large herbivores necessitates large predators who evolve to continue to be able to take advantage of the food source. All extant large animal systems work that way today.

I was amused to see one program that speculated that tyrannosaurs were scavengers because their estimate of local carcass abundance was in line with the energetic requirements of a carnivorous scavenger with a reptilian physiology...when tyrannosaurs almost certainly had an avian physiology. So local carcass abundance wouldn't have been sufficient to sustain them at all! They're not giant two-legged crocodilians, for crying out loud. It was someone from the British Museum too, I think. Darwin help us. I'm not saying they didn't scavenge too, of course. As for the bone-cracking thing: don't wolves have the ability to crack the bones of their prey also?

 

[S.A.M.]

I've always thought of T Rex as one of those deaf blind tottering old cantankerous men in a Dickens novel (like whatzisname's father who kept whining and moaning and generally testing the patience of his long suffering son).

 

[GeoffP]

On basis of the ornithiscian hip structure and presumed mobility, I expect them to have a faster gait. Although, even if slow, they'd be fast enough to catch saurischians like brachiosaurs and the like. Given that he probably couldn't be carrion-supported, they'd almost certainly have to bring down the big ones.

 

[one_raven]

Given that he probably couldn't be carrion-supported...

Why is that a given?

 

[GeoffP]

Someone in the UK worked out carrion carrying ratios based on a savanna model. They estimated there'd be enough to support a crocodile physio of that size - but T rex had a bird physio.

 

[Anti-Flag]

I think tyrannosaurs were pretty quick, actually: not as quick as in Jurassic Park or something but fairly fast - 25 kph?

probably somewhere between 10-25mph, no idea what that is in kph, but
given how long it would likely take to get up to speed and how long it could most likely sustain it, unlikely to be built for a chase. This would also require more frequent hunting as it uses more energy(like cheetahs compared with other savannah predators). I'd have to say the T-rex is more of a hyena than a cheetah.

I also don't agree with the assessment by some 'experts' that the small forearms precluded predation: diatrymas and the whole "terror bird" family were top predators for - what? 10 million years? - and didn't have functional forearms either. Neither does any predatory flying bird of the modern era, but they still occupy a position as top predator in the absence of mammalian ones.

Agreed, although comparison with birds doesn't work, they use talons to catch prey(effectively hind legs if you're comparing it to a ground creature), their other limbs are their wings. Obviously a T-rex is on the ground and needs it's legs to walk and has no wings. The sole weapon of the T-rex is it's bite.

I think the biome-wide existence of large herbivores necessitates large predators who evolve to continue to be able to take advantage of the food source. All extant large animal systems work that way today.

Agreed.

I was amused to see one program that speculated that tyrannosaurs were scavengers because their estimate of local carcass abundance was in line with the energetic requirements of a carnivorous scavenger with a reptilian physiology...when tyrannosaurs almost certainly had an avian physiology.

Some people reach for silly things to justify their claims. You'll have to explain to me how they calculated 'carcass abundance' in the first place, though you did say they estimated so they probably just made it up.

So local carcass abundance wouldn't have been sufficient to sustain them at all! They're not giant two-legged crocodilians, for crying out loud. It was someone from the British Museum too, I think. Darwin help us

.
That's rather embarrassing for them. Have you got a link for the study by the way I'd be interested in reading it?

I'm not saying they didn't scavenge too, of course. As for the bone-cracking thing: don't wolves have the ability to crack the bones of their prey also?

I'm not sure, I'm not so familiar with them, I know they're pack hunters but are they not also known to scavenge? Or be descended from scavengers of a harsher climate? It's quite a useful trait to have really.

 

[Anti-Flag]

On basis of the ornithiscian hip structure and presumed mobility, I expect them to have a faster gait.

Depends what mobility and balance reports you read! It's also likely that if they could reach high speed a fall would be enough to kill them due to impact forces.

Although, even if slow, they'd be fast enough to catch saurischians like brachiosaurs and the like.

Very much so, but even being a T-rex would you want to take on something that size? Especially when it's moving as part of a herd.
I think it'd definately take a lame or young one though if it strayed. I've have said being a predator of that size it would be rather opportunistic.

Given that he probably couldn't be carrion-supported, they'd almost certainly have to bring down the big ones.

I'm going to repeat what I said above and ask for the link. I find it hard to believe they could accurately estimate this as there are considerable variables.
I'm going to stick to believing it an opportunistic scavenger for now.

 

[Anti-Flag]

This is one of those issues that leaves me scratching my head. Why would anyone, even an expert, have such an emotional reaction to such an hypothesis? I'm sure there are very plausible just-so stories on both sides, placing T-Rex as a hunter or as a scavenger. If the experts are presently marshaling evidence on both sides of the debate, why should I (or anyone) be opposed to simply admitting "We don't know whether and to what extent the T-Rex was a scavenger or a predator"?

Perhaps I am not sufficiently emotionally invested in dinosaurs, but if the Experts are debating the question, then it seems like that should be good enough for me until some more definitive evidence is found and shared.

It's really that anyone who has an interest in dinosaurs probably believes T-rex to be the king of the beasts, ferocious predator and expert hunter etc.
They take great offense in being told a theory that he may have picked the bones of the dead. Much like the reaction of people when they were told dinosaurs were most likely related to birds and feathered and not scaley reptiles.
It takes away the whole meaning really, seeing as dinosaur means terrible lizard.
Oh how some of us laughed.

 

[Klitwo]

It's really that anyone who has an interest in dinosaurs probably believes T-rex to be the king of the beasts, ferocious predator and expert hunter etc.
They take great offense in being told a theory that he may have picked the bones of the dead. Much like the reaction of people when they were told dinosaurs were most likely related to birds and feathered and not scaley reptiles.
It takes away the whole meaning really, seeing as dinosaur means terrible lizard.
Oh how some of us laughed.

It's probably safe to assume that T-Rexes had their 'bad hair' days too. You know, a little grumpy, ill manored and hard to please. Now when it came to 'eating' was probably at the top of their priority list.

 

[sniffy]

I think, for what it's worth, that T didn't get to 'high' speeds of too often. Given the size of its head wouldn't the slightest thing trip it up even with the tail counter balancing it? It would presumably be running alongside something almost as fast as itself and without larger front claws wouldn't be able to grab the prey. It could head butt it or take a swipe with it's jaws but....it just doesn't seem feasible to me. And the thought of it waiting patiently in the bushes until something wanders by for it to ambush well it's quite a funny thought and it doesn't quite wash somehow.

Big head, big jaws, little paws = small scale hunter/large scale scavenger. Or it jumps on its prey from above.....

 

[valich]

I'm not going to dwell on the rif-raf but what predator today isn't also a scavenger? This makes the question mute. All predators, all carnivores, all mammals, all dinosaurs evolved from earlier small synapsids that developed into diapsids and therapsids that were the size of a mouse after the Cambrian Explosion. And before that we were all fish - like Pikaia.

Jack Horner is the expert in this field and he suggests Tyrannosaurus was exclusively a scavenger. This question can never be definitively answered, yet I respect Jack Horner way too much to disagree entirely. But with speeds up to 45 mph you'd think it would be able to chase down anything. And it certainly had the teeth to be a carnivorous predator. I have nothing more to add to the above posts.

 

[iceaura]

Wolves don't have the kind of jaw power a real bone-crusher like a hyena owns - predators don't, usually, because it would slow them down.

The T-Rex head looks a lot like a hyena's, the long legs (distance, not accelleration, the key) and large olfactory organs reinforce the impression.

Lots of scavengers, like hyenas, also predate on the side.

The T-Rex teeth are grooved like a Komodo's. These grooves in Komodos enable an odd combination hunting/scavenging tactic - they harbor bacteria from carrion, so that a minor bite on a large and unruly prey animal will often turn septic - and the Komodo will come across the corpse, or the disabled and more vulnerable animal, later.

 

[Anti-Flag]

But with speeds up to 45 mph you'd think it would be able to chase down anything.

You've been watching too much jurassic park!

And it certainly had the teeth to be a carnivorous predator.

Carnivorous I imagine we can be sure of, I'm not sure it's teeth have much influence on whether or not that makes it a hunter or scavenger.