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Re: Sauropod browsing energetics



On Thu, Mar 24, 2011 at 5:22 PM, Augusto Haro <augustoharo@gmail.com> wrote:
> At equal mass, the cost would be the same in a long-necked animal than
> in a short-necked one, for the latter would have to maintain an
> equivalent mass in other parts of the body.

That misses the point; to establish a selective pressure favoring a
longer neck you have to show the neck itself is energetically
beneficial; you have to hold the other parts of the body the same
(otherwise you're arguing over whether there's an energetic benefit to
a whole host of other changes).  That means the two animals cannot be
equal in mass, because the one with the longer neck HAS to mass more.

If a longer neck is going to be energetically favorable to low
browsing, then it's not enough to show that a long neck saves you some
calories while browsing - you have to establish that the cost savings
is greater than the cost of having the long neck in the first place.
If not, then there must be some other selective pressure(s) driving
the evolution of those necks.  Holding mass constant is a simple
methodological mistake and should not have happened (and frankly it
should have been caught in peer review).

> In addition, we should assess which animal of equal mass required more
> energy to harvest a given area: if one moving a long neck and walking
> relatively less, or other walking more with a short-neck.

Again, it's simply a mistake in this case to try and hold mass
constant, as doing so introduces too many confounding factors.  To be
fair to the authors, they were not claiming that low browsing had to
be the only selective pressure driving neck elongations, but they
_were_ claiming that low browsing is more energy efficient with a long
neck, and to demonstrate that they need to account for the increased
cost of having a long neck.

Cheers,

-Scott

-- 
Scott Hartman
Scientific Advisor/Technical Illustrator
(307) 921-9750
www.skeletaldrawing.com