Re: Long Bone Scaling in Neosauropod Dinosaurs

[Michael Habib <mhabib5@jhmi.edu>]

> The interpretation seems to be that large animals simply move much more
> carefully than smaller ones: they don't need to be athletic since they
> don't need to deal with all that dangerous messing about with predator
> avoidance that constrains smaller animals.  Likewise, perhaps, with
> sauropods (despite that fascinating thread a few months ago about big
> theropods attacking their necks).

Even with predation, large animals have multiple 'methods' for 
mediating the stresses on long bones, such that they can be more 
gracile than expected under isometry.  The manner in which the limbs 
are held changes with size, for example (which McN. Alexander has 
noted, as have several other comparative biomechanists).  Since bone is 
usually stronger under axial compression than bending or torsion, 
straightening the limbs reduce the bone strength required to maintain a 
given safety factor relative to maximum loads.  There are also often 
changes in gait, which large animals can get away with because of 
longer strides (and perhaps a lessened need for rapid speed, at the 
very largest sizes).  Such 'gait shifting' actually seems to play a 
role in other forms of locomotion, as well, though the relevant 
kinematics are obviously different.

Cheers,

--Mike H.