Ask a Biologist Q&A / Tyrannosaurus rex -- predator or scavenger?

Stegve · 01-03-2007 02:37:20

What is the current thinking on the feeding strategy of T. rex? I like the idea of him as a fast-moving, deadly predator, as in Jurassic Park, but some evidence seems to show that he was too big to run very fast. Then again, there would have to be an awful lot of large corpses lying around which were killed by something else to maintain a significant population of tyrannosaurs if they were merely scavengers.

John Hutchinson · 01-03-2007 12:13:03

I think most reasonable paleobiologists think that T. rex was a carnivore. In other words, it ate meat when it wanted to, and if it had to kill that meat to do so, it was sufficiently able to accomplish the dire task. I've produced some of the research that infers that it was not a super fast speed demon, but have always been careful to point out that this applies to its large prey (Edmontosaurus, Triceratops, etc) as well. (Additionally "very fast" is all relative; my models suggest 10-25mph top speed, which isn't a slouch by most standards, but still not the extreme 35-50mph bandied about in older popular accounts)

Were the arms too small? Who cares. The head was huge and full of teeth that have been shown to be able to produce and withstand huge bite forces. Sharks, hyenas, and in fact most carnivores (except cats and a few oddballs) get by without arms.

The evidence that it had a good sense of smell, could scavenge effectively, and so on is all not only consistent with it being mostly a scavenger, but is also consistent with it being a carnivore that does both.

The "controversy" that it was either a scavenger or predator is hence a false dichotomy that can be swiftly dismissed. It is mostly perpetuated by the media and a small number of high-profile scientists, one of whom claims to not be a big fan of T. rex (but talks and writes about it more than almost any other animal!). :-)

Graeme Lloyd · 01-03-2007 12:24:02

Hi Stegve,

As far as I'm aware this is still a hotly debated topic and will probably always remain so. The fossil record can tell us a lot about the history of life, but any behavioural aspect is always going to be hard to prove. For example we can be very sure that T. rex was a meat-eater. This is because it has the serrated teeth of a carnivore, T. rex bite marks have been found on various herbivorous dinosaurs and crunched up bones have been discovered in faeces attributable to T. rex.

However, behaviour is less confidently assigned. The limitations on running speed in T. rex are absolute, but whether this hampered their ability to hunt depends on the speed of their prey. However, even if they were 'too slow' they could have got by as ambush hunters so this proves nothing.

Similarly the total number of large carcasses available to T. rex is hard to estimate as we have no reliable figures for relative abundance of predators to prey. Also, we don't fully understand the metabolic efficiency of dinosaurs (the hot-blooded/cold-blooded debate is still raging) so we don't really know how much T. rex would have to eat to stay alive. Although Michael Brett-Surman (at the Smithsonian National Museum of Natural History in the US) and James Farlow (at Indiana-Purdue also in the US) did once try and estimate the number of lawyers you would need to feed a T. rex in a year. Their estimate was 292 if T. rex was warm-blooded, and 73 if cold-blooded.

If we assume they were cold-blooded then it's possible that one decent-sized carcass could keep a T. rex going for a year.

Perhaps the best evidence for behaviour in the fossil record comes from trace fossils (footprints, burrows, coprolites etc.). Unfortunately, although we have plenty of dinosaur trackways they have yet to provide any definitive answer to your question.

I could continue for a long time on this, but my general point is that there are too many 'ifs' and 'buts' to answer this question satisfactorily. In any case the predator or scavenger question has one implicit flaw - it assumes that it must be one or the other. From observations of modern predators we know this is simply not the case as many animals will eat both carrion and live prey.

So my question to you would be why couldn't T. rex be both?

#1 01-03-2007 02:37:20

Tyrannosaurus rex -- predator or scavenger?

#2 01-03-2007 12:13:03

Re: Tyrannosaurus rex -- predator or scavenger?

#3 01-03-2007 12:24:02

Re: Tyrannosaurus rex -- predator or scavenger?

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