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Re: dinosaur humps

David Marjanovic wrote-

> > Such vertebrae as found in dicraeosaurids would
> > have undoubtedly made a hump instead of a sail, given their great
> > transverse diameter.
> So the idea of 2 sails is dead?

I was referring to the dorsal vertebrae of Amargasaurus, not the cervical
vertebrae (which do seem to have parallel sails).

> Another question... considering the extreme case *Spinosaurus*, what would
> a hump be good for when it was 1.8 m high and would shift the center of
> gravity considerably forwards in a biped?

The first question that would have to be answered is- Where was the center
of gravity of the neural spine structure?  Assuming Lapparent's
reconstruction is roughly accurate in vertebral position (which is
uncertain), the neural spines' height increases quickly on the anterior
dorsal area, then only slightly to the sacrum.  Sacral neural spines are
unknown, and the caudal may not belong to the specimen.  If Spinosaurus was
similar to baryonychines, we would expect that the sacral neural spines were
tallest, and the height gradually decreased through the long caudal series.
This would probably place the center of gravity of the dorsal structure over
the hips, which is ideal for a theropod.  Also, the structure would probably
not be as massive as many of you think of when visualizing a hump.  It would
have basically made a triangle defined by the transverse processes and
neural spine, which is fairly narrow.

Mickey Mortimer