Re: hyper-elongated cervicals

["Jaime A. Headden" <qilongia@yahoo.com>]

David Peters (davidrpeters@earthlink.net) wrote:

<There are other taxa with hyper-elongated necks. Plesiosaurs, tanystropheids,
including Dinocephalosaurus, and azhdarchids. Can one assume that what works
for giraffes and sauropods also works for these?>

  This is a "I just woke up" answer, but my first impression of this would be
"no."

  Giraffe's and sauropods appear to have functionally distinct necks in terms
of mobility, including the capability of dorsoventral movement in the latter
not really present in the former along the neck's length, whereas in giraffe's
most of the dorsoventral movement is at the trunk-neck and neck-head junctions.
Mediolateral movement would alow both animals to potentially pick bits off
their backs, but Stevens and Parrish seem to show that sauropods probably were
incapable of reaching their own trunks with their head. This saurop[od-like
flexibility, rather than giraffe-like, seems present in long-necked
protorosaurs like *Tanystropheus* and *Dinocephalosaurus*, which appear to have
solved the issue of neck-length convergently due to one having vastly more
cervicals involved per neck length than the other, a condition that is also
apparent in plesiosaurs, so that the cervicals are really rather short.
Plesiosaurs also appear, while they have very, very short cervical centra on
the whole, relatively inflexible rather than whip-like, necks, due to the
intervertebral articulations and range of movement possible between elements. I
would like to see Kent Stevens turn his perspective for a moment to plesiosaurs
and model the necks of these animals, as some other work on the issue is
currently limited and/or unpublished (see Richard Forrest's comments at
http://dml.cmnh.org/2003Jan/msg00341.html), and I suspect movement possible in
the longest-necked of elasmosaurs will be very similar if not more restricted
than in sauropods Stevens and Parrish have looked at.

  Jim Cunningham, on the other hand, also has first-hand experiments testing
the range of movement possible in azhdarchid necks, and while not published
(damn it, Jim!), they would appear to show an extremely limited range of
movement perhaps on par with giraffes or less flexible at the neck-back
transition. Most movement seems to have been possible in a dorsoventral range
of movement and at the head-neck transition.

  So giraffes and sauropods seem to have different cervical capabilities
involving flexibility along the column with emphasis on either dorsoventral or
lateral movement, or none at all, depending on your group, in which manner the
flying long-necked pterosaurs likely solved the problem by restricting movement
almost entirely as in giraffe cervical columns, and plesiosaurs simply
increased the count of cervicals to increase flexibility in a stiff neck.
Others retained some measure of flexibility inherently.

  Cheers,

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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