Re: Lizard engines and rat engines
- From: dkomo <dkomo871@xxxxxxxxxxx>
- Date: Sun, 10 Jul 2005 20:28:11 -0400 (EDT)
g wrote:
> "dkomo" <dkomo871@xxxxxxxxxxx> wrote in message
> news:dak4st$eco$1@xxxxxxxxxxxxxxxxxxxxxx
>
>>g wrote:
>>
>
>
>>And it jars me to see someone make a statement like this, which to me is
>>akin to ignorance. Elephants have big ears for very *specific* reasons.
>
>
> ???
>
>> Being so large and living under the blistering sun of the African
>>savannah, African elephants have severe problems with potential
>>overheating. Their ears are an important way of dissipating much of
>>this body heat.
>>
>
> Let me see if I'm getting this right. If the why of it is that larger
> animals
> have big ears because of their size and the temperature of the climate
> where they live, then giraffes and ostriches have ears that are not as large
> because they are smaller and live in a cooler climate. And Indian elephants
> are smaller and live in a cooler climate, which explains why theirs are
> much smaller. And jackals have larger ears for their body size than
> rinoceroses because they are larger than rinos and live in a hotter climate.
>
> Now that's ...
>
> Uh oh, wait...
>
> No that's not right...
>
> Dang ! For a minute there I almost thought I got it.
>
> (:>)
>
> g
>
>
There's nothing that says evolution has to converge on the same solution
to a problem (big ears for big mammals in a hot climate). As far as
other large bodied African mammals, Lavers has this to say:
"We are now, at last, in a position to answer the title question of this
book: Why do elephants have big ears? Or, to put it in its comparative
form for those who already know the answer but not the reason, why do
elephants have big ears when rhinos, giraffes, and all the other
warm-blooded mammals toiling under the African sun do not? The crucial
difference between elephants and all other land animals is probably
size: the mismatch between the amount of metabolic heat produced and the
amount of skin through which it can escape tends to increase as animals
get bigger, and elephants are fully twice as heavy as any of their
savanna neighbors. So being bald like a rhino is not enough. Elephants
need some additional way of ridding themselves of excess heat, and large
flat ears densely packed with tubes through which hot blood can be
pumped are a rather neat solution."
_Why Elephants have Big Ears_, p. 18
If we look at closely related animals we may detect a pattern that
wouldn't be present by looking at disparate animals. The African
elephant actually has two species: the savannah or bush elephant, and
the little-known forest elephant from the equatorial woodlands of
central and western Africa. In addition to the African varieties, there
is also the Indian elephant. The Indian and forest elephants inhabit
shaded woodland where temperatures are much lower than on the savannas.
Though Indian and African forest elephants have ears that are huge by
normal mammal standards, they are considerably smaller than the enormous
flaps that grace the heads of their bush-dwelling cousins. Also, there
is the extinct woolly mammoth. It was as huge as the African bush
elephant but lived in the very cold climate of Siberia. Though mammoths
of Siberia were majestic beasts in many ways, there is one anatomic
department in which they were distinctly lacking compared with their
living relatives: they had tiny furry ears.
Another comparison of ears is between the fennec fox of the Sahara
desert and its cousin Arctic fox. The fennec fox has huge erect ears --
6 inches long for a body size of about 2 feet. They are cooling
radiators. The Arctic fox has tiny pinned-back ears covered by thick fur.
Finally, I found the presence of the ostrich in the comparisons above a
bit hilarious. The ostrich is a bird and one of the main
characteristics of birds is that they don't external ears for
aerodynamic reasons. In fact, I thought that *no* birds had external
ears until I did some checking and found an illustration of a great
horned owl which shows it with what appear to be ears (or they could be
tufts of feathers -- hard to tell). The other species of owls,
including the barnyard owl and snowy owl are quite "bald" when it comes
to ears.
--dkomo@xxxxxxxx
.
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