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Re: Sauropod ONP...and energetics



First of all, a few of the posts here have devolved into somewhat personal critiques of both Kent and Greg's work/comments, and since I helped start this discussion, I want to offer up my apologies to both of them. Niether Kent nor Greg are dishonest, and the somewhat personal tone of a few of the posts the last week or so was not always fair. Obviously at least one of them is wrong (or possibly both, or one or the other depending on the sauropod...). This will be a sort of eclectic response to a nummber of things posted this week:

As Jaimie says, Kent does deal with the discrepancy in his papers between ONP and LNP. I think it is fair of Greg to say that there is more work to be done here (e.g. on multiple giraffe specimens) both to establish true LNP in extant animals and to evaluate individual variation in ONP, but it is also a reasonable working hypothesis that the "average" position you would see a sauropod in.

On the other hand, there are other apatosaur specimens that have a good arch to the dorsal column, including the UW specimen in Laramie. And if Apatosaurus has a strong downward arch, then either the neck must be commonly held out of ONP (i.e. ONP does not equal LNP), or else ONP has been misreconstructed, possibly because of diagenetic alteration.

Jaimie also points out that he has reconstructed Opisthocoelicaudia with an almost straight back, but then so has everyone else. This doesn't really add credence to the idea that all saurpods (let alone all dinosaurs) had almost straight backs, because everyone finds the data in agreement for this taxa. It is noteworthy that everyone (including Kent) seems to be inagreement that Dicraeosaurus had a downward arched back.

Of course, unlike all long-necked sauropods, dicreaosaurs were actually adapted for low browsing. Don't belive me? Ok, considering how insanely cheap it is to for large animals to move (locomotion scales to about the 0.75 power with mass, so the biugger you are the cheaper it is move), what possible enegergetic benefit is conveyed to a sauropod who has a long neck to "stand still" while it eats? Especially when it will have to burn calories ALL day EVERY day to support the growth and maintainence of that tissue> Worse, if the food source is patchy, then the animal will have to move a few steps anyways to acquire new folliage, while still supporting that long neck. WORSE, a long neck necessitates a long thin trachea, which drmatically increaes drag from laminar flow, so the animal has to burn even more (probably substantially more) calories just to breath, every breath it takes every day for its entire life.

Please, someone, explain how on earth a long neck is of benefit to any grazer/low browser?



Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(408) 483-9284

www.skeletaldrawing.com

-----Original Message-----
From: Jaime A. Headden <qilongia@yahoo.com>
To: dinosaur@usc.edu
Cc: gerarus@westnet.com.au
Sent: Thu, 19 Jan 2006 05:16:41 -0800 (PST)
Subject: RE: Sauropod ONP

Christopher Taylor (gerarus@westnet.com.au) wrote:

<One thought that seems obvious, but I'm not sure if it has been mentioned
(unless it was what Greg Paul was saying) - resting position and feeding
position of the neck were not necessarily identical.>


Kent has also said this, in fact made a large provision for this in his
agreement with Greg Paul on the matter. Kent has used the modelling of the
vertebrae tou project maximal curves of neck vertebrae when infering various
percentiles of disassociation between zugapophyses while keeping the centra
connected. The issue, I think, is that some restorations and arguments would
imply that sauropods were engaging in neck elevating postures as a matter of
course, rather than constantly held horizontal. Similarly, if we consider the
sauropod "hoover-saurs" feeding mechanism by sweeping the neck around side to
side, we should in fact note that constant movement would be the norm, but that
some movements, i.e., side to side, yeild greater envelopes than others (up and
down). Thus, Kent argues the constraint in envelope extent shoudl warn us about
not just maximal movements for a given disassociation of neck bones, but also
general postures resulting from this.


I noted earlier in this thread that artistic renditions of several argued
sauropods would have us think the average posture of the neck was elevated
(that is, in non diplodocoids, anyway), but the data on paper and as modelled
argues otherwise. Why a sauropod would raise its head above the floor so high
and risk blowing its head off without the use of theoretical arterial valves (a
theory to substantiate a theory seems shaky logical ground!) to slow the
pressure of fluids back into the brain, when there is an ample shoulder- or
foot-level supply of vegetation or the occassional squirrel to be had, I do not
know.


It is clear that, in the same formation, in the same level, we do not seem to
get the same kind of sauropod neck at once, indicating possible constraints on
sauropod speciation and discretion in envelope patterns. In the Morrison, my
only regret is that we lack a neck for *Haplocanthosaurus* in which to consider
its relation to *Apatosaurus*' medium, *Diplodocus*'s long, *Barosaurus*'s
superbly long, and *Camarasaurus*'s short necks. *Brachiosaurus* seems to have
specialized in slightly higher vegetation, but the same foods were likely not
in resource competition between sauropods, as dentition tells us that different
foods were preferred, so where neck length may overlap, teeth and skull design
would seem to differ. The same should be true for the Shaximiao sauropod
faunae, where *Omeisaurus* and other "mamenchisaurs" exist in the same
formations, and tooth and neck discrimination may indicate resource
partitioning. So it seems rather more romantic and "aesthetic" to raise the
neck and argue that contradictory theories would be wrong.


We should also consider straightening the spines of sauropods BEHIND the
shoulders as well, and other data is indicating the same for most theropods,
since ventrally-wedged dorsals seem rare to my knowledge. I've had to resist
bowing the dorsal series in my own restorations despite their elegant effect,
and find instead that an elegant sort of curve and thorax is produced by the
natural increase in neural spines and consequently dorsal vertebral height
posteriorly, and in the increasing pelvic depth, and the position and
orientation of the pectoral girdle. Much supported by fossil data on scapular
position and the trickier issue of how the specimens are arranged in life. I
find a little ease of mind comes from erring on the side of caution when
invoking taphonomic principles of muscular and tendinous contraction and
diagenic distortion of the bone itself, and consider this when reconstructing.


I've only reconstructed the skeletons of two sauropods, one of a mount of
*Mamenchisaurus* and one of *Opisthocoelicaudia*. In the former, I restored it
following the mount, including dorsal arching, but held the neck horizontal for
ease. In the latter, however, I attempted to articulate the dorsals and caudals
neutrally, and found they form a largely straight line. I have no data to
consider this is not in fact an accurate position for them in life. If
restoring movement in skeletons, one should of course consider that the slopes
and curves will increase or decrease as neccessary, but when providing a
skeleton that is largely static, there is no reason to diminish the
effectiveness of the restoration by exaggerating features for "effect".


 Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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