Re: scavenging T rex

[George Engelmann <engelman@cwis.unomaha.edu>]

> 
>       
> 
> Although the gut reaction against the notion that the creature we all learned
> from our childhood to be an awsome hunter/predator was actually a loathsome
> scavenger is understandable, I don't see any really good reason for such a
> prejudice. In fact, although few carnivorous creatures can be described as
> either pure predators or pure scavengers, and I think it unlikely that we
> could ever conclusively resolve a question of such dietary detail for a 
> fossil,
> I think the idea has much merit. There are a number of reasons to suppose that
> it would have been much easier for a T rex to survive primarily on the remains
> of already dead critters than to catch and kill them herself and there are 
> good
> ecological reasons for the existence of such a creature. Horner argues that 
> the
> forelimbs are so reduced as to be ineffectual in prey capture and yet are far
> from functionless. This seems like a resonable conclusion as it is difficult 
> to 
> imagine how such limbs could have assisted in capturing prey. Perhaps they 
> were 
> used for food manipulation or mating somehow. But that wouldn't stop T rex 
> from
> capturing prey by some other means, such as seizing it in its jaws. On the 
> other hand, why would a lineage in which a well-developed prey capture 
> structure
> is primitive reduce that structure while maintaining its predatory habit? 
> There could be an answer, but it is a troubling question nonetheless. 
> Studies of modern predators suggest that larger predators not only can, but 
> must
> rely on larger prey for reasons of effort vs. reward. Thus, the largest 
> predators often have a very restricted diet. It's lonely at the top of the 
> food pyramid. A T rex would probably have to expend considerable effort in
> finding or following suitable food species. If it relied chiefly on predation,
> it would then have to expend the effort of catching it. As a scavenger, all
> it would have to do would be to find it. Why would carcases be any easier to
> find than live prey? Well, a carcase of a large beast might be expected to
> stay in one place for a lot longer than a live one. This would not be the case
> for the remains of smaller animals which would be consumed by smaller
> scavengers rather quickly, but a large carcase may not be accessible to 
> smaller creatures until it is broken into by something large enough and
> powerful enough to do the job, like a T rex. Among vultures, one of the few
> animals that are virtually exclusive scavengers (at least some vultures), 
> there are specialists whose function is sorted out by size. The largest
> vultures (king vultures in South America and Griffin vultures in Africa) are
> the only ones capable of breaking into the body cavity, so the others must 
> wait for them to feed before they can get at those morsels. Vultures may
> be one of the few exclusive scavengers because they can travel long 
> distances to find food. On a day-to-day basis, the distribution of carcases
> is probably not very dense. Very large animals can also travel long distances.
> It would need long, powerful legs but would not need to be built for speed, 
> rather like T rex. Perhaps power walking is not a bad way to put it. Vultures,
> of course can see their next meal and fly right to it. An animal on the ground
> could not do that so it would need a keen sense of smell to orient to and
> localize its food and then walk right to it. It wouldn't matter if it took a
> few days to get there. Nothing else could get into the carcase until it 
> arrived
> (except another T rex and there wouldn't be very many of them around). Large
> teeth and a powerful skull and jaws would be needed to cut through the 
> tough hide and break up the carcase. As for the ability to gulp large bites, 
> although a large bite might be a good way to inflict killing damage on large
> prey, there is no particular reason that a predator need actually consume
> large portions in the act of killing, most don't. But, if your only 
> competition for a meal were another of your own kind who could show up at 
> any moment, there might be good reason to bolt your food. All of this 
> merely argues that the scavenger interpretation is at least as consistent 
> with 
> the facts about T rex as the predation interpretation but we may never be able
> to know better.
> G.F.Engelmann  engelman@unomaha.edu  
>