[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Jobaria and the Elephant Commit Suicide

Nick Pharris writes:
I believe (and correct me if I'm wrong) that the Sereno team's findings
indicated that the femora were three times as strong as they needed to be *to
support the animal in the rearing position*.

Okay, but more to the point: are these animals bending their knees while rearing or are they straight? If straight, the weight would be borne in compression. If bent, then tension and some torques plus compression will be happening to the femur. If the figures they have suggest it can bear 3 times its weight in rearing, that's all good and fine: but in what position are the femora? This can make a big difference. Sereno et al have shown pictures of sauropods rearing with bent knees, and from what I saw at their website this was the case with Jobaria. Bones do well in compression, but don't do as well in tension which is what is going to happen if their legs are bent while rearing. Safety factors in all animals are pretty high, but they don't normally attempt to do things that would push these factors.

Nick further writes:
I suppose the caudofemoralis would be stretched if the animal were trying to
sit on its cloaca, human-style, but I think the femur would actually be
*retracted* to bring a sauropod into the classic rearing pose, since the
vertebral column would be rotated up to a subvertical position. The pose in
which the caudofemoralis really would be stretched is when the animal
squatted, a position we are now fairly confident at least some sauropods
could achieve.

Again, how far the vertebral column could rotate up is dependent on a variety of factors. If you are using the femur as the pivot point in rearing, the further you tilt that vert column back, the further the pubis rotates forward and thus the more the pubic adductors are stretched. This would seem to limit the amount of rearing that would happen. Plus, while the insertion site for the caudofemoralis would remain fixed, it's origin on the tail would move -- what happens there has still been largely underinvestigated.

Furthermore, we are not fairly confident that at least some sauropods could squat. I'm not sure what you are referring to here. My suspicion is the report by Larry Martin and Craig Sundell at SVP this year with the Camarasaurus? They have found incredibly nice C. supremus specimens, one of which appears to be "squatting," if by this you understand that the femur, crus (tibia and fibula), and pes are all pancaked on top of one another. This is "squatting" in a very loose sense -- all the bones are completely disarticulated from one another.

Matt Bonnan

Get Your Private, Free Email at http://www.hotmail.com