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Re: Long Horizontal Necks Re: Vertebrae of Early Sauropods



> Date: Tue, 30 Mar 2004 23:35:20 -0800
> From: "Eric Martichuski" <herewiss13@hotmail.com>
> 
> In order to move from one clump of foliage to another, the sauropod
> can either
> 
> A) move it's entire multi-ton bulk...and then do it again for the
> _next_ clump, and the one after that; all of which engages a large
> number of muscles and puts added strain on bones, tendons, etc.
> 
> or
> 
> B) move its much lighter (relatively) neck...and this movement can
> suffice for a great many clumps of foliage before a step needs to be
> taken.  In contrast, think about how much movement the _entire_ body
> of, say, a zebra would have to undergo to graze through as much
> plant life as a single neck-sweep would cover.
> [...]
> I'd actually thought this feeding strategy was already accepted as a
> given for some species.  Obviously much less connected to current
> thinking than I'd assumed. ;-)

I don't think _anything_ about sauropods is universally accepted :-)
But it's true that the feeding method you describe does seem to be
widely _assumed_ to be correct, just like Jack Horner's Obligate
Scavenger thing -- and perhaps with just as little justification.

I think the idea of sweeping-neck low-browsing originated in a short
paper by John Martin in 1987:
        MARTIN J. (1987): Mobility and feeding of Cetiosaurus
        (Saurischia: Sauropoda) - why the long neck?.  Occasional
        Papers of the Tyrrell Museum of Palaeontology #3 (Fourth
        Symposium on Mezozoic Terrestrial Ecosystems,
        Drumheller). pp150-155
But the idea's really taken hold in the wake of Stevens & Parrish's
DinoMorph paper in 1999, which, helpfully, is freely available on-line
at
        http://www.sciencemag.org/cgi/reprint/284/5415/798.pdf

The DinoMorph paper _appears_ to show that _Diplodocus_ and (to a
lesser extent) _Apatosaurus_ were limited to a range of neck movement
that keeps the head relatively low, rather than allowing them to adopt
the traditional swan-necked high-browsing posture.  If that's true,
then it doesn't seem to leave many other uses for the long necks than
side-to-side sweeping, or possibly feeding below foot-level at the
margins of lakes and rivers.

But I say it _appears_ to show this because there are a lot of
unanswered questions about the DinoMorph work.  Apparently there are
papers in press that clear a lot of issues up, but until they make it
out there we're limited in what we can usefully say on the subject.
Anyway, not everyone's convinced that the DinoMorph models reflect the
reality.

As for your argument that sweeping the neck is less energetically
demanding than just walking up to food -- well, that has yet to be
proven (or even, I think, analysed).  Even if it's true in terms of
sheer muscle-power exertion, bear in mind that maintaining a long neck
is very energetically demanding even when you're not using it: you
have to get blood up and down it, air in and out, feed all all the 
ligaments and muscles that keep the neck off the ground even when it's
not moving at all, plus there are all the extra dangers of life with a
long, fragile neck.  So it may well be that when you roll all those
factors in together, side-to-side sweeping with a long neck is much
more depanding than walking up to bushes and eating them with a head
on a short neck.

So what _were_ sauropods doing with their long necks?  It's the great
problem.  The obvious answer -- high-browsing -- may yet to turn out
to be correct.  It certainly makes ecological/evolutionary sense.  It
just suffers from the one tiny detail that it seems to contradict
everything that the anatomy is telling us :-)

 _/|_    _______________________________________________________________
/o ) \/  Mike Taylor  <mike@indexdata.com>  http://www.miketaylor.org.uk
)_v__/\  "Every action has an equal and opposite criticism" --
         Steven Wright.

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