Re: late night thoughts: misunderstand what?

[don ohmes <d_ohmes@yahoo.com>]

Interesting, but a little hyped, in my view. Still, I like the approach.

Repeating basic assumptions/opinions here... barring data, we will probably 
have to agree to disagree.

1). Well-placed crushing bite (1 Erickson unit (EU) of bite power*), 'instant' 
incapacitation. When the spinal cord is out of commission, instant limpness. 
Convulsions come later.
2). Neck is not strong enough to move, swing or support multi-ton weight placed 
away from shoulders (distal to mid-point of neck). Particularly after injury 
from crushing bite. They were herbivores, not draglines.

Biped weighing 4000 kg grabs sauropod by head. A shake of the head, and biped 
is flung into the woods? I am skeptical. In other words, I think the 
well-placed crushing bite was _perfect_ for killing long-necks.

Reductio ad absurdem: if your body is as big and as mobile as Mount
Shasta, and your neck is as big as a pencil, are you a 'huge' opponent?

Further--

A ropewise pull by the neck would move most anything, but where is the risk? 
Just let go. I have some experience with that, working w/ ropes and large trees 
and it is instinctive and easy. Just don't let it get a wrap on you... of 
course, you can temporarily kiss the skin on your hands goodbye, if you aren't 
wearing gloves.

One kill per 3 days? Well, maybe. That's a lot of meat, though. If that is a 
reasonable budget, that points up the advantages of a group life-style for 
utilizing large units of food. Seems a little high, to me. 

Anyhow, at 1/10%, I get .999^2400= .09, or 9%. Heh, could be wrong, 'math ain't 
my deal', and I used excel. No offense to Mr. Gates. The other point is that 
even I don't call for juveniles to be killing adult sauropods, which cuts way 
down on critical events. Say 3 days, 8 years? So, .999^(8*120)= .38.

The bottom line(s)-- 
1). I still think the big sauropods were easy prey for tall bipeds w/ powerful 
jaws, if and only if, those jaws could be wrapped around the neck, preferably 
at or close to the head. 
2). The peculiar vulnerability of the sauropod physique was the reason they 
went so overboard on size (trying to keep those necks out of reach). 
3). A patient still-hunting strategy had a high chance of success for the large 
bipeds, and therefore the running speed of *T. rex* is not much of an indicator 
in the predator vs scavenger question. This of course gets away from sauropods 
entirely, as such a strategy is not sauropod-specific. However, in my personal 
cartoon, the biped/sauropod interface was what pushed them to such ridiculous 
sizes.

* just made that up... equals max bite power of adult *T. rex* (as DM would 
write it).

Don

----- Original Message ----
From: Graydon <oak@uniserve.com>
To: dinosaur@usc.edu
Sent: Thursday, June 14, 2007 7:04:54 PM
Subject: Re: late night thoughts: misunderstand what?

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