Re: SAUROPOD NECKS & "VICTORIAN" ILLUSTRATIONS

["Matthew Bonnan" <mbonnan@hotmail.com>]

Hi Darren:

You wrote:

"-- The models of Kent Stevens et al are therefore the best argument for
the presence of relatively inflexible necks. However, these have been
criticised by those who know sauropod morphology very very well and
the only published results thus far concern diplodocoids, a group
already thought by most to be horizontal-necked."

I don't think Stevens or Parrish say that the necks are inflexible.  Rather, 
that the base of the necks cannot be raised above shoulder-level in the 
diplodocids Apatosaurus and Diplodocus.  Diplodocus appears to have had less 
lateral flexibility than did Apatosaurus (see their illustrations in the 
1999 Science paper), but both animals have relatively flexible necks 
dorsoventrally, and especially ventrally.

Criticisms about the neck position seem to stem from the idea that in 
mammals the discs between the vertebrae can be thick and can add to the 
flexibility of the neck.  However, the centra (bodies) of the cervical 
vertebrae in most mammals have flat anterior and posterior ends.  In 
contrast, sauropods have ball-and-socket style centra that fit together in 
certain ways.  Yes, you can pack the spaces between the vertebrae with 
vertebral discs, but you reach a point where the zygapophyses (the joints at 
the anterior and posterior ends of the verts that allow the verts to 
articulate and move against one another) come apart.  So far as I know, 
disarticulation of zygapophyses does not occur even in camels and okapis.

Parrish has already begun some preliminary dissections on okapis, and the 
plan is to expand this research to include more vertebrates, both extant and 
extinct.  The idea is to manipulate necks with all soft tissue, including 
cartilage and ligaments, present (in extant vertebrates, of course!), and 
then to do the same with just the bones and see what the differences are.  
Should be exciting.

"-- Those who work on tooth microwear seem pretty confident that
diplodocoids were not feeding at ground level."

This comment stems from the idea that only conifers and other woody plants 
could cause dental microwear.  However, horsetails, which contain silica, 
were abundant during the Jurassic and especially in the Morrison Formation, 
and a low-browse diet that included horsetails could also contribute to 
dental microwear.  As Tracy Ford alluded to earlier, there appears to have 
been more biomass on the ground (ferns, horsetails, cycadoids, etc.) than in 
the canopy.  This is not to say diplodocids could not rear, and did not feed 
from conifers, etc., but tooth microwear could be caused by other plants as 
well.

"Shame about the horizontal-necked macronarians
though...:)"

I know.  I LIKE Camarasaurus with a more vertical neck, and even McIntosh 
said if Camarasaurus has a more horizontal neck it was a shame.  However, 
very preliminary results from Parrish and Stevens seem to indicate that the 
neck of Camarasaurus may not have been as vertically oriented as was once 
suspected.  For those of you on the list who want to see something 
unsettling but interesting, check out Osborn and Mook's 1921 paper on 
sauropods where they restore Camarasaurus, not just with a horizontal neck, 
but with a neck that slopes to the ground!!  I don't think Parrish and 
Stevens have argued that -- yet! =)

Take care all,

Matthew F. Bonnan, Ph.D.
Department of Biological Sciences
Western Illinois University
Macomb, IL 61455
(309) 298-2155
mbonnan@hotmail.com
MF-Bonnan@wiu.edu

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