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Re: Sauropod browsing energetics



I agree with all of that.  I was hugely disappointed when I got this
paper, since it promises to address an important question that I've
not known how to address.  Problem is, the paper presents no evidence
that the authors know how to address it, either.  And their model is
grotesquely inadequate.  What a shame -- a real missed opportunity.

-- Mike.



On 23 March 2011 20:40, Scott Hartman <skeletaldrawing@gmail.com> wrote:
> On Wed, Mar 23, 2011 at 2:44 PM, David Marjanovic
> <david.marjanovic@gmx.at> wrote:
>
>> Yeah, if.
>>
>> Without studies of neck mobility beyond the current controversy, and studies
>> of locomotion cost beyond Paul's back-of-the-envelope calculation which
>> suggests this cost was very low indeed, and studies of the cost of holding
>> the neck horizontally and of raising it (assuming the bones allowed both,
>> see above), this conclusion sort of hangs in the air.
>
> My objection is the paper simply looks at the cost of moving vs the
> cost of standing still as viewed against their estimation of browsing
> envelope expansion with neck elongation.  Which is great, but they
> aren't figuring in the extra cost of having the long neck (e.g. M is
> held constant)!  All that extra tissue in the neck has to be grown and
> maintained like any other part of the body; plus mechanically speaking
> simply having the longer neck necessitates greater muscle exertion
> _all the time_ (less so if held upright, but still extra work
> regardless), and of course more work breathing in through a longer
> trachea (although this is partially mitigated if you assume
> flow-through lung ventilation...which we should).
>
> If having a longer neck didn't cost you anything, then of course it
> would make low-browsing more energy efficient.  Walking may be cheap
> in large animals, but nothing is cheaper than free!  The real question
> should be "what is the extra cost to maintain that longer neck 24/7
> (and also how it impacts survival to reproductive age) and whether
> THAT cost is lower than the energy saved while browsing with a longer
> neck?"
>
> That actual comparison between models of browsing simply doesn't
> happen in the paper, so it's failing to test what it claims to be
> testing.  To be sure, their model should be useful to future attempts
> at modeling the energetics of sauropod food acquisition, but their
> claim to have demonstrated a selective advantage for long necks in
> browsing is completely false.
>
> -Scott
>
> P.S. As a smaller pet peeve; as far as I know it's universally
> acknowledged amongst locomotion researchers that the cost of
> locomotion goes down with size as a percent of your daily energy
> budget (hence the "smaller than 1" scaling factor in the equation they
> publish).  So why do they keep referring to moving the "enormous mass"
> of sauropods, and keep citing size as a factor behind neck elongation
> and browsing?  If "neck elongation and not walking" is going to be a
> browsing advantage for anyone, it should be especially so for smaller
> vertebrates who have to spend a larger amount of their daily energy
> budget per unit distance moved.
>
> --
> Scott Hartman
> Scientific Advisor/Technical Illustrator
> (307) 921-9750
> www.skeletaldrawing.com
>
>