Re: Jobaria and the Elephant...

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

Mike Lovelace said, in relation to my comment on sauropods possibly breaking 
their bones if they fell with their forelimbs on a predator:
> I am a little confused by this.  As an example, when we (humans) perform a
> push up, we are using the contraction of the Triceps (primary), and upon
> descent from the apex of the maneuver we use the Triceps as a control
> mechanism for a smooth descent.  I don't know what the name to apply to 
> this
> other than a controlled relaxation of the Triceps group.  I am not going to
> argue behavior on rearing for defense, I have a preference to functional
> morphology.  I will say this, yes it could raise up, from a functional 
> stand
> point, the why is speculation at this point.  As for any sauropod with a
> structure capable of rearing, it would have a controlled decent, there is 
> no
> compelling argument to suggest otherwise (the gravity doesn't change, and 
> the
> acceleration of descent wouldn't overcome the control of a muscle group
> strong enough to raise it in the first place).  Thanks

We shouldn't compare humans with sauropods, although I see what you're 
getting at.  All sauropods (except titanosaurs) have a reduced or absent 
olecranon process.  What this means is that most sauropods had relatively 
vertical limbs most of the time.  Their triceps muscle (probably a misnomer, 
since gators appear to have five heads for this muscle) would not have had 
the same sort of lever arm we see in graviportal mammals.  You have an 
animal that already has a straightened out arm most of the time.  Are you 
proposing that they bent it and then pushed off with it?  From what I can 
tell, the bending of the forelimb wasn't very common.

We don't know for sure if sauropods could rear, in large part because we 
don't understand the biomechanics of these animals that well.  In time, we 
may have a better answer to your questions, and others that have appeared on 
this list.  For now, much is speculation or using the behavior of elephants 
to justify certain behaviors.  As I have already noted, we must be careful 
when using analogs because there is a tendancy to carry these too far.

Hope this helps,

Matt Bonnan

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