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Re: bloated T. rex



>Dear Jaime,
>Re: your response-

>>I gather from your use of the word 'waddled' that 
>>it would have been. This leaves me curious. Would this mobility 
>>impairment-- 

>>>1) have been due to outward displacement of the legs due to an 
>>>increased volume between?

>>There is a large volume to the tyrannosaur trunk, literally 
>>barrel-chested, and implying that theropods had bird-style lungs, 
>>those and the heart would only take about one-sixth the volume of 
>>that area; the liver would be about another sixth, and the stomach 
>>(based on a carnivore) would be one-and-a-half--sixths, and the 
>>intestines would take up the rest, with some spilling through the 
>>pelvic canal. With most of the stomach taken up in the latter half 
>>of the trunk, where the femora swing up, there would definately be 
>>expansion and a need to alter the gait, such as a slow walk, rather 
>>than a high-stepped trot or even a run, which in most living animals 
>>today is virtually impossible.

>Thank you for giving me some more detailed proportions on this.  I 
>gather from your other remarks that the proportion of the volume >taken 
up by the stomach would have been highly variable.  Were these 
>proportions derived by analogy with other animals, or is there 
>actually any direct evidence on this?

I would assume so. In AMNH 5438 (this is a *Daspletosaurus*) there is a 
large portion of the rear half of the trunk (over two-fifths total 
volume) uninhibited by confining vertebrae, though the narrow gastralia 
do constrict a bit. The vertebrae have a general movement of about ten 
degrees outward, and this helps, but the gastralia are also loose from 
each other in the posterior half of the belly, and this could mean they 
would be free to expand downward to about another eigth or so of volume 
to the trunk. Now, given daspletosaur mouth volume (you could fit in it, 
for example) and the amount of room inside (close to six cubic feet, 
based on NMC 8506) the tyrannosaurid could swallow close to a human 
about average size---say, a 160 lbs or 73 kg. That would take six whole 
humans (not to assume daspletosaurs ate humans, of course :) ) to fill 
that belly at constricted volume. Now increase that by a plausible five 
cubic feet, and close to seven of us would completely fill that creature 
up (1090 lbs or 493 kg). I might add that the area between the shoulder 
blades would not allow a human to squeeve through, so the daspletosaur 
would have to have taken a few bites out of us.

But this is about a rex, so I'll use another specimen (AMNH 5027 for 
example) to illustrate this: say, 17 cubic feet (big skull), that's over 
seven cubic feet inside, and it's strait down the gullet where the 
pectoral girdle would have allowed such a volume (remember JP?) and then 
to the gut. There was a smaller degree of expansion on the rex as there 
was on the daspeltosaur, but it was a much larger creature, fully 
one-third bigger, and this is not the biggest rex specimen, but I use it 
for its relatively complete trunk. _Nine_ of us could end up down there 
(1440 lbs or over 650 kg) and this is with an expansion possibility of 
one-seventh volume or so. That's a third of a hadrosaur of relatively 
average size at 30 feet and four tons or so in the time it would take a 
small family (seven or so, given mine) to eat a roast turkey and taking 
time to swallow and wipe one's lips.

>>>2) have been due to having to rotate the thighs forward to keep the 
>>>feet under a forward-displaced center of gravity? (Squat-walking, 
>>>in other words.)

>I didn't know whether to attach any significance to your lack of 
>comment on this one. My impression is that you were attributing the >T. 
rex's mobility impairment primarily to volumetric expansion >interfering 
with the action of the legs, or is that an >overextrapolation of your 
view? In other words, do you think putting >a couple of tons of meat in 
the stomach would have had any effect on >the rex's center of gravity? 
Just looking at a rex skeleton, (eg. the >one at 
http://tyrrell.magtech.ab.ca/tour/trex2.jpg ) it is hard for >me 
personally to imagine the stomach having been located far enough >back 
that this kind of weight would not have seriously tipped the rex 
>forward. I notice the balance problem in large carnivorous therapods 
>doesn't seem to particularly bother most people in the field, (take a 
>look at http://tyrrell.magtech.ab.ca/tour/alberto.html for what looks 
>to my inexperienced eyes to be a *serious* case of imbalance) and I >am 
trying to figure out why. I'm assuming the most likely explanation >is 
that the experts know something about this issue that I don't, and >I'm 
trying to find out what that is.

A duck waddles because it is front heavy, I assume, but I think I've got 
it right. No counterbalancing tail, for instance. And while a rex would 
be front heavy with 1.5 tonnes of hot, fresh (or rotting) meat in front 
of it's hips, all he would have to do would rotate his body up in the 
front, the tail swinging back and forth behind like a tightrope-walker's 
balancing pole, and waddle forward, and this position may be a reason 
why the legs and hips are so broad and developed for muscle, to support 
the forward-heavy body.  Normally, the center of gravity is right under 
the preacetabular bar of the ilium, but with all that extra weight put 
on, it moves forward about two feet (.45 meters) or so, and to 
compensate, the rex must move it back or he's ("she" in the case of Sue, 
we assume) in trouble of toppling. The duck waddle would be one of the 
few gaits allowable under such conditions, for it requires little 
femoral movement. The tibia and fibula support this as well, for they 
are very strait compared to the relatively curvaceous shins of smaller 
and lighter tyrannosaurs like *Albertosaurus* and *Daspletosaurus*, who 
would be less hindered by such balance-altering mass compsumption.

>>>3) have made the well-fed rex vulnerable to other rexes?

>>How many rex-inflicted wounds did Sue have?

>Good point.

>>>I do know other predators can consume a large proportion of their 
>>>body mass,

>>The taxa *Hyaena,* *Acionyx,* and *Leo,* though I don't know the 
>>ratios, can consume huge volumes of meat in little time (six lions, 
>>weighing on average 450 lbs, can take down a wildebeest weight two 
>>tons, and can consume such in hours to the bare bones, leaving very 
>>little behind for jackals and vultures to take advantage of; 
>>cheetahs, on the other hand, will eat a gazelle weighing their own 
>>100 lbs. ave. of mass all by themselves, or less with cubs 
>>participating---or a pair---and eat it bare; the hyena, like the 
>>lion, consumes huge volumes of flesh per mass more than any animal I 
>>know, probably half their mass).

>Interesting about the cheetahs.  I hadn't known that.  (But if a 
>cheetah can eat something equal to it's own mass, wouldn't that beat 
>the hyena eating up to half of it's own mass?)  However, all these 
>examples are of quadrupeds who store their meals slung between four 
>points of support.  Do you think it is safe to extrapolate by analogy 
>to a biped who stores it's meals forward of two points of support?

You've got a point. My assumptions are based on scavenger-predator 
relationships and habits. Most birds store their meals directly under 
their hips, so the balance altering of bipedal theropods doesn't apply 
well. There are few (if any) living bipeds that store their meals in 
front of the hips, so we must extrapolate from two similar examples of 
the spectrum on either side of tyrannosaurs (mammals and birds). All 
living reptiles, being bipeds or flippered forms, do not apply thus, for 
none that I know of scavenge except perhaps crocs. (Don't know enough 
about crocs to say "yea" or "nea", so ignore this.)

There may be something in the metabolism of hyenas compared to cheetahs, 
where the latter has a higher rate of food-to-energy ratio than the 
former, and packs of hyenas are also a facter, while cheetahs hunt 
alone.

>Just wondering,

>Nicholas

You've got me thinking.

Jaime A. Headden

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