(The dinosaur, not the rock band).
I remember this being debated many years ago. Has the question been settled yet? What are the arguments for each position?
Wikipedia suggests that the binocular vision and bite marks on other dinosaurs show that it was unlikely to be just a scavenger - at least, it could scare off a bunch of smaller predators like lions do to the hyenas or cheetahs which actually made a kill.
The possibility that it had feathers is simply delicious. If I found myself in Jurassic Park confronted by what looked like a toothy Big Bird whose mother had taken thalidomide during pregnancy, I don’t think I’d know whether to crap myself or laugh out loud.
I’ve always thought this was a silly debate. Almost every carnivore alive today is both a predator and a scavenger. Why can’t T-Rex be both?
Indeed, it could have been (and likely was).
Recent fossils have shown that T. rex grew very rapidly. It is possible that as juveniles, they were active hunters (being relatively unburdened by the biomechanic stresses that the adults would face), and gradually turned to scavengery as they aged.
At any rate, the essence of the argument can be found here. Needless to say, the issue is not yet resolved, since most evidence either way is circumstancial (though it is mentioned in that article that evidence of bones scarred by tyrannosaur teeth that later healed would be good evidence for predation).
I think the only reason this idea lives is because people think it’s so cool (“Wow, the biggest carnivore ever was really just a whimpy scavenger!”) and they want to believe it whether or not it makes any real sense.
My recollection is that the whole “T-Rex is a scavenger” thing was started decades ago by a guy who looked at some T-Rex teeth and found that, to him, they didn’t appear to have signs of being worn down. He took this to mean that T-Rex’s were only eating soft, already rotten, meat.
But of course there are plenty of T-Rex teeth that show wear. And, as the the dino book I have said, T-Rex didn’t have six-inch serrated teeth, a four-foot jaw, a skull with large bony projections to anchor the largest jaw muscles ever, binocular vision for accurate biting, and huge well-muscled running legs just in order to eat rotting carcasses!
And if T-Rex was a scavenger, then it’s relatives and ancestors would also have to be scavengers, as even down to medium-sized therapods were built pretty much the same way.
Plus there are no known large land animals that are exclusively or even mostly scavengers. Hyenas hunt and kill most of their own food. The only large scavengers are condors and vultures which can cover vast distances to find and quickly get to and bodies.
Of course there’s no ‘proof’ T-Rex actively killed. I mean, there are no authentic videos of T-Rex’s attacking anything. But what ‘proof’ is possible from fossils?
And Mr. Finch – if biomechanical stresses were a major problem for a full-grown T-Rex, how did natural selection create such a large creature? I mean, wouldn’t there be significant selective pressure for smaller size?
From what I understand, the T-rex in the original Jurassic Park movie was animated to be as close to what a homoeothermic tyrannosaurid carnivore would be like if one were alive today as was possible given the state of CGI at the time. In other words, if one could observe a T-rex in the flesh, its physiological capabilities and constraints would be very close to those of the animal in the movie.
Lions, as we all know, are facultative predators/scavengers – they will hunt their own prey or consume the prey of others, either seizing it from them or scavenging off older kills, as circumstances make most convenient to them. But remember that lions operate in prides; they’re not solitary hunters.
Tigers, on the other hand, are almost completely predatory, and solitary hunters. And T-rex fossils are not found in groups, but rather as solitary skeletons (or, more often, parts thereof). To me this infers a tigerlike rather than lionlike lifestyle – but I note the large assumption leap that that conclusion makes.
One quick point, however, is that Tyrannosauridae are not members of Carnosauria, the other big carnivores like Allosaurus and Ceratosaurus, but rather a divergent group of Coelurosauria, the small carnivores. So perhaps the closest parallel in modern animals would be the cheetah, which is so divergent from the other cats as to almost warrant a separate family, and preserves a lot of characters from the viverrid (civet) group that have been lost by the other big cats.
What this is saying is that you have small, light carnivores – then, the coelurosaurs; today, the weasels and foxes – and large carnivores – think the bears and big cats – but that the tyrannosaurs were giant forms of the small-carnivore group, not the largest members of the big-carnivore group. A close relative of Allosaurus is the largest carnosaur. (Hoping I have my terms right on this – the facts are correct, but IIRC Theropoda [the carnivorous dinosaurs] includes Carnosauria and Coelurosauria, rather than switching the first two around. If I’ve swapped the terms in my head, read “theropod” for “carnosaur” and my statements will be accurate.)
A lot of the recent debate has been spurred by Jack Horner, a hadrosaur expert. In my opinion, he’s simply trying to get his name in the papers and is talking out his hat; this conclusion is somewhat borne out by the fact that most tyrannosaurid experts disagree with him.
His contentions seem to be thus:
T. rex had small arms, and thus could not grapple prey.
Rebuttal: Wolves have no arms, and take prey just fine. Crocodiles don’t use arms. African wild dogs have no arms. Phorusrachids don’t have arms.
**Endocasts of T. rex skulls show they had a large olfactory lobe, thus a good sense of smell to find carrion. Only kiwis and vultures have propotionally larger olfactory lobes. **
Rebuttal: There’s been no recent work done on dinosaurian olfactory capabilities. In order to do comparative anatomy, you really need something to compare to. Did all dinosaurs have large olfactory lobes? Did other predatory dinosaurs?
Also, vultures are certainly scavengers, but kiwis are omnivores, so the comparison isn’t particularly compelling.
**T. rex couldn’t run, and thus could never have captured prey. A high tibia to femur ratio is indicative of being able to run. **
Rebuttal: The tibia/femur ratios that are given as comparison are of smaller predators. As size increases, the tibia/femur ratio tends to drop – but T. rex has the largest tibia/femur ratio of any animal its size, and better than the large herbivores it might have preyed upon. All it needs to do is be faster than the slowest member of a herd and lunch is served.
Some biomechanical estimates put T. rex speed at 20-30 mph, which is pretty darn fast if you’re on foot, and faster than most large prey animals of its time. Even if it couldn’t move fast, it could have been an ambush predator, needing only a single lunge and bite to capture prey.
T. rex’s eyes were too small so it couldn’t see well enough to hunt.
Rebuttal: There is no evidence that T. rex’s eyes were too small. The ratio of eye size to body size generally decreases in larger animals. There’s no reason to think that a larger body somehow makess eyes work less efficiently. Also, T. rex had adaptations towards stereoscopic vision; Horner tries to explain these away by saying that they’re inherited from its ancestors, but the features aren’t present in basal tyrannosaurids, so it seems like T. rex was increasing its fitness for stereoscopic vision, which is hardly important for a scavenger.
Also, there was some talk of a triceratops pelvis with a toothmark in it that had later healed, which would be clear evidence of hunting. During the late maastrichtian, who else would have made that toothmark? There really weren’t any other large predators available. I’m not sure what the final conclusion was on this.
As for T. rex looking like Big Bird, we needn’t worry about that. There have been some tyrannosarid skin impressions found and these showed scalation rather than feathers. These were of course partial imprints, so it may have had feathers somewhere, but it’s unlikely it would be totally feathered. We know that mammals are furry, but elephants aren’t particularly – this is because, with a sufficiently large mass to surface ratio, insulation becomes a detriment rather than an advantage.
The idea was not my own, I was simply summarizing the argument. Folks such as R. McNeil Alexander have done studies which, to them, demonstrate that an adult T. rex could not have been an active runner. Others, such as Gregory Paul, disagree. Personally, I am in the “probably both hunter and scavenger, as opportunities either way presented themselves” camp.
Ceratosaurs aren’t carnosaurs, either. The Carnosaur-Coelurosaur split occurs within the Avetheropods, which excludes both Ceratosauria and Torvosauroidea (spinosaurs, “megalosaurs”, Afrovenator, etc.).
Darwin’s Finch said
Fair enough. And upon re-reading my post was a little snarkier than I meant.
But my Q is are there any good web links for Therepod classification? My recollection was that Tyrannosaurs and Allosaurs were not that distant.
Even better, here is the whole dinosaurian tree. There is a link to a .pdf version, which you can view in much greater detail than the image on the webpage. If you look at the blown-up version, you can see Allosaurus nestled in amongst the Carnosauria (represented by Yangchuanosaurus, and Tyrannosaurus just below, within the Tyrannosauridae. The branch that includes everything from the Tyrannosauridae on down is Coelurosauria.
Also, here is a cladogram showing all major dinsoaurian groups. Between the two, you should get a good idea of who is most closely releated to whom.
That last site doesn’t allow direct linking, apparently. From the main page, select the “Dinosauria Cladogram”, then “View complete cladogram” if you want to see the whole thing, or “Go to detail cladogram with species lists” if you want to see specific branches.