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re: Long Bone Scaling in Neosauropod Dinosaurs



Colin McHenry writes:
 > Guy Leahy wrote:
 > > Congrats to Dr. Bonnan...
 > > ----------------------------------------------------
 > >  The neosauropod sample
 > > was very homogeneous, and linear analyses revealed
 > > that nearly all humerus and femur dimensions,
 > > including cortical area, scale with isometry against
 > > maximum length. Thin-plate splines analyses showed
 > > that little to no significant shape change occurs with
 > > increasing length or cortical area for the humerus or
 > > femur. Even with the exclusion of the long-limbed
 > > Brachiosaurus, the overall trends were consistently
 > > isometric. These results suggest that the mechanical
 > > advantage of limb-moving muscles and the relative
 > > range of limb movement decreased with increasing size.
 > > The isometric signal for neosauropod long bone
 > > dimensions and shape suggests these dinosaurs may have
 > > reached the upper limit of vertebrate long bone
 > > mechanics. Perhaps, like stilt-walkers, the absolutely
 > > long limbs of the largest neosauropods allowed for
 > > efficient locomotion at gigantic size with few
 > > ontogenetic changes. 
 > > -----------------------------------------------------
 >
 > That's just so wierd.  If I didn't know any better, I'd say that
 > the isometric scaling strongly suggested an aquatic habit....

And yet isometry or near-isometry is much more common in limb bones
that we'd naively expect.  McNeill Alexander, for one, has repeatedly
made the point that the long bones of elephants are proportionally
more gracile than those of much smaller rhinos and hippos.  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).

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor    <mike@indexdata.com>    http://www.miketaylor.org.uk
)_v__/\  "Hardware is just the same as in 1990, but faster.  Software is
         just the same as in 1990, but slower" -- Ed Avis.