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Re: Jobaria and the Elephant Commit Suicide



Richard Travsky writes (in response to my which elephant? question):
The jobaria web page specifies Sereno had access to a 20 year old African
elephant named Angus.

Yes, I am aware of this. I don't think I stated my point clearly. The point is, which elephant behavior are you going to use, and why use that one particular elephant over another. While I am no elephant expert, do we know how often certain elephants rear, how their behaviors differ, etc.? We are only using an analog for potential sauropod rearing, and we must be careful not to extend these behaviors to sauropods.


I am well aware they weighed this elephant, front and back, and found a "reversed" condition of weight bearing in Jobaria. While it was great that we have the live weight of an elephant on record (most elephant weights come from carcasses), the observation that Jobaria has smaller hands than feet, the reverse of an elephant, is nothing new. I'm sure they included it to emphasize their point, but this in and of itself does not tell us that these guys were rearing up. If sauropods are descendants of bipedal relatives, this difference in hand vs. foot size could merely be a relict of their former bipedal natures.

I wonder how they calculated the femur's weight-bearing capacity? Sure, you have circumference, cross-sectional measures, etc., but how they arrived at 3 times the weight of the animal would be interesting to know. But let's say this is true. Is this "overbuilt" as has been suggested? Well, all animals have bones with safety factors, in some the safety factor can get up to 5 times the weight. 3 times falls within the range we see reported for elephants (Knut-Schmidt Nielsen, 1984, Size) so I'm not too sure the condition in Jobaria would be overbuilt ... unless they meant three times as much as an elephant -- that's a little different.

Still, let's go with the 3 times idea. When animals move their limbs, they increase the loads on them dramatically, even when just walking. From memory without a reference in front of my face, a human walking moderately fast can nearly double the normal weight going through their limbs. Something as large and heavy as Jobaria certainly would have greatly increased the force through its limb bones just walking to be sure. Now take that weight and spread it out on only the hindlimbs ... not saying this was impossible, but just something to consider.

Here's something else to think about. Maybe the bones can support 3 times the weight in COMPRESSION (i.e., when they are vertical), but less (I would expect) if they are bent. Sereno et al. give us restorations of the elephant and sauropod with BENT knees while rearing (and actually, all the restorations I have seen of Jobaria and other sauropods restored by Sereno et al have bent knees while walking). What effect does such a position have on the femur? What torques are produced? Should the femur bend, as it does in an elephant, for a sauropod to rear or is this a case of the analog leading the functional interpretation? See what I mean about the analogs being a slippery slope?

I again emphasize the Caudofemoralis longus tail muscle. Elephants have no real tail to speak of, yet the tail of sauropods had muscles which were intimately tied with locomotion. How are these tail/femur muscles being accounted for? If you bend your knees so that the femur swings forward, how far can that muscle stretch? Would such a muscle restrict how far you can rear up? At this point, I am not satisfied with current sauropod rearing explanations.

Richard further adds:
If a threat display deters a predator(s),then this is a cheap means of
survival. A lot cheaper than incurring wounds.

Seems like an awful waste of energy. Allosaurus and Ceratosaurs aren't all that big -- a sauropod is still a pretty huge animal to them. Do elephants rear to scare away predators? Are we sure that no rearing incurs wounds from predators?


Further:
Which would make it effective in defense. (Think of the noise alone!)

Yikes! When I said the crashing down of a sauropod gives me the willies, I meant that it stands an awful risk of breaking its bones, not the noise. =) Remember those weight safety factors? Imagine you are a gigantic animal that is pretty heavy and relies on all fours to get around. Would such an animal engage in activies that would push its limb bones to the extremes of their safety factors? Break a bone in your forelimb, now what?


If you rear up, how do you look down at your attacker? No matter how the neck goes together, that little head is way up there, maybe trying to look down with one or the other eye in its skull. But let's say you can. So now you're up on your hindlimbs stuck in place. You can't pivot because your femora have cylindrical heads and you have stiff-action ankles. And you can't use your tail because its on the ground as a tripodal support.

I insist we have to be careful and do more rigorous work on sauropods. Analogs are EXTREMELY tricky and we must use them with caution.

Matt Bonnan

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