Re: late night thoughts: misunderstand what?

[Graydon <oak@uniserve.com>]

On Thu, Jun 14, 2007 at 08:37:34AM -0700, don ohmes scripsit:
> "..but looks like an unnecessary risk when the prey is twice as long
> and tall as the predator." --DM
> 
> What is risky about reaching up and grabbing a sauropod by the neck,
> if you match the physical description of a tyrannosaur? If your hold
> is 2m behind the head, you are 8m away from the front feet. Even that
> assumes no injury to the spine of the prey item, which would result in
> instant incapacitation of the prey. 

Basic grappling rule; if you've got them, they've got you.

A T. rex trying to neck-bite a sauropod is not biting into a fleshy
neck; it's a very bony neck, with the vital bits fairly buried.  If the
sauropod rears, T. rex is in for a large fall; if the neck just *spasms
in death*, the T. rex is at significant risk of being flung.

Heck, wasn't one of the Utahraptor fossils found *under* a dead
sauropod, in a "you may have killed it, but it fell on you" sort of way?

Which is not to say there's no way a tyrannosaur would or could prey on
a sauropod; it's to say the they appear to have specialized in a
predation style -- placed crushing bites -- that doesn't work very well
on creatures substantially larger than yourself, because the crushing
bite isn't immediately effective at being disabling if the prey animal
is huge, and when you're a predator, the question isn't "will the prey
animal die?", the question is "am I going to get hurt doing this?"

Successful predation requires relatively low risk, and significant risk
adversity on the part of the predator, because you have to get through
thousands of predation events to old enough to have a chance to breed.

In the case of T. rex, if the long adolescence view is correct, 20 years
times (roughly) 120 successful predations/year (which may be low, that's
eating every three days), you're looking at 2400 successful prey capture
events. (and 24 _thousand_ attempts, if modern ratios hold...)

A one percent chance of significant (crippling/fatal) injury per
successful predation event means no detectable chance of surviving long
enough to breed.  At a tenth of a percent, just under one chance in a
hundred of living until you're old enough to breed; hundredth of a
percent, just better than three chances in four.  Thousdandth of a
percent, nearly certain to survive long enough -- a two and a half
percent chance that you'll die young.

None of that is anything other than back-of-the-envelope, and we don't
have enough predatory theropod fossils (except possibly from
Allosaurus?) to look at the age distribution at death to try to figure
out the kind of risk level being run, but it should serve as an
indication that predators are, in general, extremely cautious.

-- Graydon