Re: Jobaria and the Elephant Commit Suicide

["Matthew Bonnan" <mbonnan@hotmail.com>]

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

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