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Re: Body size for mammals



At 07:08 PM 5/1/98 EDT, Dinogeorge wrote:
>In a message dated 98-05-01 03:21:53 EDT, jhecht@world.std.com writes:
>
><< In any case, John Alroy of the Smithsonian tested Cope's law by comparing
> the masses of successive species of North American mammals, estimated from
> the size of their first molar teeth (a technique verified with living
> mammals), and found that the average increase from one species to the
> successor species in the same genera was 9.1%. This verifies Cope's Rule,
> that animal sizes tend to increase, at least for the North American
> mammals, which were what Cope studied in the first place. It may not hold
> for other animals. >>
>
>Ahh---! (Need I say more? But remember--it's just a tendency, not a "rule.")

But this leaves a number of things uncontrolled.  For example, North America
has grown steadily cooler since the Cretaceous.  Cold adapted endotherms
tend to be larger than their warmer-weather cousins, probably for the simple
reason that size (other things being equal) reduces the surface - volume
ratio and so reduces heat loss.  Still, 9.1% is a big number.  Maybe bigger
than gradual temperature change could account for ...

  --Toby White