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Re: Rigid dinosaurs

OK: "reaches to the skull or at least the axis" is about as good a
functional definition as I've seen for ligaments' qualification for
the adjective "nuchal".  (From what I've seen in the speculative
sauropods-with-nuchal-ligaments literature, the term seems to be used
to indicate a single continuous ligament as distinct from a series of
short ligaments that span only one, two or three segments each.)

Yes -- the latter matches the physiography of the avian elastic ligament system, for which there's good evidence in many non-avian dinosaurs, too. And you're correct about how the term "nuchal ligament" _sensu_stricto_ is typically used: as a continuous structure unattached or indirectly attached (via laminae) to the cervical vertebrae extending from the cranial thoracics to the skull or Cv2.

(You should _so_ publish on this :-)

Working on it! Much to say about nuchal ligaments, and I think I've only just tapped the keg!

Well, what else _is_ there?  I don't see how a ligament embedded in
the cervical soft tissue can be a sexually selected (which is of
course the usual get-out clause for Inexplicable Mystery Morphology).

Me neither! I just meant I haven't yet come up with a good hypothesis about what kinds of non-sexual selective pressures guided the evolution of _Rhea_ toward having a nuchal-ligament-like elastic ligament system. To get one, I'd probably have to know more about what things the system in _Rhea_ enables it to do that other birds are unable to do with the standard elastic ligament system. Time to go hang out in Argentina and play Jane Goodall with the rheas for a while!

Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT  84770   USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
and     dinogami@gmail.com

"Actually, it's a bacteria-run planet, but
mammals are better at public relations."
                                     -- Dave Unwin