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Re: Sauropod browsing energetics



2011/3/24 Scott Hartman <skeletaldrawing@gmail.com>:
> 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.
>
I do not think such a large host of other changes is necessary:
accounting for shape you only need a change in proportion whether or
not maintaining the same mass (i.e., change in the relative size of
the neck). At equal mass, it may seem one has to take as a further
change (in addition to neck mass increase) the decrease in size of the
rest of the body, but given the prolonged ontogenies, adult
reproductive status well below maximal size and individual size
variation this may not be quite problematic, and the relative size of
the neck is not great compared to the rest of the body, and likely
within the range of adult size variation. However, we need just one
change, keeping equal the harvesting spending time, metabolism, and
proportion of food used for mass growth, which would end up with a
similarly massed animal, if the neck increase is the side effect of
diverting a larger share of the energy destined to growth for neck
increase.
A mass increase would likely require not only a longer neck, but also
relatively more powerful torso to support it (perhaps also at equal
weight), more powerful (thicker and thus larger) limbs to support the
extra weight, and then we may end up with a way larger animal, where
the advantages or disadvantages of the longer neck alone may end up
being difficult to discern.
So, I think both an equal-mass proportional change and an absolute
mass increase with neck elongation may result from a single change.