Re: mammal mystery

[John Bois <jbois@umd5.umd.edu>]

On Mon, 17 Feb 1997, Ronald Orenstein wrote:
> 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).

I accept that my view is not an absolute rule.  However, I think it's
relevant that no dinosaurs, after a point in the cretaceous, managed to do
what the sharks have done: develope derived rat-sized relatives.  They
were essentially closed out of the small animal niche by, among others,
mammals.