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Re: dinosaur humps
Mickey Mortimer (email@example.com) wrote:
<<Such vertebrae as found in dicraeosaurids would have undoubtedly made a
hump instead of a sail, given their great transverse diameter.>>
David Marjanovic (firstname.lastname@example.org> wrote:
<So the idea of 2 sails is dead?>
I doubt anyone has been able to figure out what was between the paired
spines in *Dicreaeosaurus hansemanni* or *D. sattleri*. However, the
condition in *Amergasaurus* is distinctly different in that instead of
being transversely expanded they are transversely narrower than
craniocaudally long. Though parallel, the cervical to anterior half of the
dorsal spines are very slender and blade like. This distinction has not
yet been expanded into an anatomical restoration showing what is more or
less likely to occur given musculature. Such a thing has not been done for
any tall-spined dinosaur yet, in fact. This begs a study (likely in
progress) in actually finding more osteological correlates in the bones
for muscular associations. The epaxial musculature in sauropods, for
instance, has received little to no attention, whereas the corresponding
laminae have received much recent attention.
It seems likely that there were "sails" of light muscles and skin
between the vertebral spoines for *Amargasaurus*, whereas the distally
"knobbed" spines in *Dicraeosaurus* in the cervicals show the heavy
musculature was associated with nuchals. The dorsals likely bore these
tendons and ligaments, but not, as far as I can tell, to what degree.
Comparatively, *Diplodocus* has much smaller distal expansions, greater in
dimension craniocaudally than transversal, yet the condition of a "sail"
versus hump is not raised for this taxon. The anterior dorsals of
*Brachiosaurus* show a great transverse expansion not reflected in more
anterior cervicals or distal dorsals, probably related to the
ungulate-like nuchal region that has been hypothesized by some to hold the
neck up at a single cantilever (whereas in hadrosaurs and theropods, the
necks are braced by multiple dorsolateral and sequential cantilevers,
anchored by the shorter neural spines and the epipophyses.
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
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