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Re: Sauropod Necks



"Jaime A. Headden" <qilongia@yahoo.com> comments on Carpenter's
reconstruction of _Diplodocus mayi_ (cf. Stevens and Parrish's
computed reconstructions):

> No discrepency; but I and several others who observed the mount
> noticed that not all the cervical alignments were flush, or even
> close, and to acheive the position, there were problems articulation
> some of the dorsals.

If you're claiming that the specimen was mounted in an unnatural pose
I suspect you're going to hear from Ken...  In any case, I asked him
about it before Jaime wrote the above, and he gave me some background
on what LN Jeff brought up.  Before mounting the specimen he laid out
the anterior dorsals and all the cervicals on their sides and propped
them up on sand bags and pieces of wood so that they were all in the
same plane.  Range of motion around the joints was constrained by the
zygapophyses and cartilaginous scars on the "balls" of the centra (I'm
not sure exactly how the scars constrained the rotations, though a)
Ken may tell me in response to this message and b) the answer may be
contained in a reference Ken mentioned that I haven't dug up -- a
chapter by Carpenter, Madsen and Lewis in: _Vertebrate Paleontological
Techniques_, edited by Patrick Leiggi and Peter May, Cambridge
University Press, Cambridge, 1994.)  Since Parrish and Stevens used
the criterion that maximal displacement was achieved when the
cartilege was precumably stretched "taut", this might be a major
source of any discrepancy in the respective results.  That is, the two
groups may have been using a different criterion to decide whether or
not the vertebrae had slipped as far as they could go.

Jaime also says:

> That is to say, the model did not mean the neck couldn't go above
> horizontal, but that the head could not be raised above ~8ft
> (~2.5m).

Let this be a warning to everyone who tries to wing numbers off the
top of their heads (irrespective of their neck postures :-)...
Parrish and Stevens actually claim that _Diplodocus_ could raise its
head to a level of around 4 m (a bit over 12 feet); to use their
words: "_Diploducus_ was barely able to elevate its head above the
height of its back".  That's what I'd have meant by by "horizontal" in
this context, and I suspect it's what others have meant as well.

> This gives the neck a gentle U-shaped curvature, hypothesizing that
> the first dorsal is horizontal in oritentation, an assumption the
> paper promised to resolved with further testing.

I confess I didn't completely re-read the paper, but I searched it
(literally searching on the word "dorsal" as well as skimming over it
and carefully reading all the parts that seemed likely to have such a
statement if it were actually there) and I didn't find any such claim
about the first dorsal or what they might do about it in future
research.  Get some rest, Jaime :-)

-- 
Mickey Rowe     (rowe@psych.ucsb.edu)