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Re: cause of Gigantism in sauropods



2011/2/12 Habib, Michael <MHabib@chatham.edu>:
> Good thoughts.  A quick clarification here is needed, however. The cervicals 
> of sauropods had fragile walls from a preservation standpoint. Mechanically, 
> however, they were generally quite strong in bending. In order to maintain 
> this strength in bending at large body sizes,  where structural constraints 
> are more intense, without excessive mass, the vertebrae must be thin walled 
> which makes them weak to local impact. However, in mechanics "local impact" 
> means something more akin to point loading. When using the neck as a weapon, 
> or having it pulled on by a predator, bending loads would dominate.  By 
> contrast, an animal being struck by a weapon (club, spike, tail, etc) is 
> likely to suffer a local impact.

Thanks for the physical explanation. Now correct me if I am wrong, but
would not the neck also suffer a local impact in the point which
hitted the theropod's head? I would tend to think that the contact
area at the impact would be the same between both animals, and perhaps
more local in the larger animal (in this case the sauropod) than in
the smaller, on which the load would seem to be more distributed. May
you be meaning sauropod vertebrae are better at transforming these
impacts into bending loads (which are better dealt with) than theropod
heads or necks?

I do not know if there is physical reason for my prejudicious idea
that when two things (for example, sticks) of similar density collide,
the one moving with greater velocity tends to break up the other
instead of the reverse; if this is true, the theropod would be worstly
affected. Gregory Paul (in Predatory Dinosaurs of the World) indicated
that theropod bones are denser than in other dinosaurs; if this is
true for sauropods: can the animal with less dense bone, in virtue of
its greater velocity, break the denser bones of its antagonist easier
than getting his own bones broken?