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RE: Elasmosaur necks

The flexibility of plesiosaur necks has perhaps been the object of more
speculation than hard scientific investigation. Zarnik (1925, Sketologiji
plesiosauriija, sa prinosima mehanici kraljeznice u recentnih sauropsida;
Societas Scientiarum Naturalium Croatica, Hrvatskoga Naravoslovno Drestva;
vol 38-39, pp 424-473) investigated the range of movement available, and
this work was extended by Mark Evans in his MA thesis (as yet unpublished,
in spite of all attempts at persuasion by Arthur, myself and others). His
findings showed a limited degree of flexibility in Muraenosaurus and
Cryptoclidus, especially in the vertical plane. However, these studies do
not deal with only two taxa, the taxonomic status of both of which is
uncertain. The range of movement described by both of the studies is also
very dependent on a number of unknown variables, such as the vertebral
spacing. With neck extending to 72 vertebrae in length, a very small change
in spacing can have a major effect on the range of movement available.
There are fairly tight restrictions on the range of vertical movement which
I demonstrated in my poster presentation at the SVPCA in Cambridge last year
(which I will write up as a paper, promise). In some elasmosaurs (whatever
they might be) , the neural spines of at least part of the neck interlock -
there is a tongue and groove arrangement so that the leading edge of the
spine slots into a groove on the next. This must restrict movement in the
vertical plane considerably.
>From a hydrodynamic point of view a stiff neck seems essential. Plesiosaur
limbs are equipped with powerful musculature to drive them through the
water, and it seems unlikely that they swam very slowly (or backwards).
Bearing in mind that plesiosaurs are handicapped by a poor hydrodynamic
profile anyway - the long neck preceeding the body is highly inefficient -
it seems unlikely that they would make matters worse with a very flexible
neck, which would demand a large energy investment simply to hold it stiff.
The general consensus of the Leicester Marine Reptiles Research Group
(Arthur Cruickhank, Mark Evans and myself) is that the neck flexiblity was
that of a stiff fishing rod.

Richard Forrest

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Sent: 18 January 2003 18:13
To: dinosaur@usc.edu
Subject: Elasmosaur necks

Richard Forrest (in speaking about Bob Nicholl's art said, << He paints
pleisosaurs realistically (i.e. with a stiff
neck)... >>
I don't have a copy handy, but I remember Sam Welles attributing a great
degree of flexibilty to elasmosaur necks in his 1943 University of
Memoir 13: 125-254, "Elasmosaurid plesiosaurs with a description of new
material from California and Colorado". I guess I'm just curious as to where
he went wrong. DV