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Re: mammal mystery



At 01:35 AM 2/17/97 -0500, George Olshevsky wrote:
>Nevertheless, extinction has been the fate of all but five species of
>rhinos--and those five are >all< presently endangered.

As that endangerment is entirely the result of human activity, including
demand for rhino horn, I would not make too much of it as evidence that
rhinos are evolutionarily disadvantaged.

It is certainly generally true that large animals in an ecosystem tend to
disappear before small ones as they have more extensive resource
requirements, may find it impossible to get shelter etc.  However, Mr Bois'
statement that an evolutionary line that does not have small forms cannot
last is not valid, though it may well be true that smaller forms have a
better chance of surviving a mass extinction.  For example, the coelacanths
exist today because a quite large form outlived its smaller relatives.
Although there are some very small sharks (six inches or so) these are
highly-derived deep-sea species; if Mr Bois' view is correct we might
expect to find, instead, that these were basal forms.  Instead, the most
primitive living sharks are also large fishes (eg the frill shark, sixgill
and sevengill sharks).
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net