Re: Bipedalism in different substrates

From: Bob Keeter (rkeeter_at_earthlink.net)
Date: 06/23/04 

Date: Wed, 23 Jun 2004 00:28:37 GMT

"Pauline M Ross" <pmross@ross-software.co.uk> wrote in message
news:ne1gd0116280fn7vgt5a625nqdkln6i0l4@4ax.com...
> On Tue, 22 Jun 2004 02:46:20 GMT, "Bob Keeter" <rkeeter@earthlink.net>
> wrote:
>
> >>[Pauline] Giraffe and eland are a couple of tropical examples [of
large,
> >>fully-furred mammals]. Can you suggest any reason why this
> >> cooling problem would not apply to them too?
> >
> >Well it has to do with surface area.. Weight, and nominally the heat
> >produced by a mammal goes up on a kind of cubic function of a linear
> >dimension. Surface area goes up on a square. [Snip]
> >Could I suggest that Big + Tropical + Endothermic is starting to become
> >a matter of hard physics, not even all that realted to paleontology or
> >opinions. If you are really interested, I'll loan you my "Heat Transfer"
> >textbook from far too long ago. [Snip]
>
> Aaargh! I think I'll pass :-) But if this sort of calculation is
> within your realm of expertise, you might want to do some sums on
> elephants and rhinos, and then on the giraffe and eland, and see if
> the difference becomes obvious. A little hard physics never goes
> amiss.

The problem here is that while body mass is easy, the surface area
of the skin would be at best a wild guess. I might still give it a whirl
but. . . .

> As I said, I don't dispute that size is a factor in furlessness, but I
> suspect there are multiple factors involved and there isn't a
> straightforward principle that mammals above a certain size or weight
> in a tropical climate lose their fur.

Name one tropical mammalian creature over the weight of 2500 lbs that has
hair!

If you say giraffe, you win the cupie doll, of course you are also probably
looking at the "worlds record holder" for surface area in a large animal. A
giraffe is long and spindly to the point of absurdity, even though a big
bull
does run up to about 4000 lbs. Hmmmm. . . . that is more than a little
bit interesting, why is a black rhino nearly hairless and a giraffe well
covered.

About the same general weight, one is long and spindly, one is solid and
compact
, , , , one has close to the minimum possible skin area for the body mass
(rhino), one spreads out all over the place (giraffe). . . . . hmmmmmmm

Even water buffalo (Asian) are pretty close to hairless!

Regards
bk

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