Who needs Popigai?

[KELL00BELL@aol.com]

    Crocodilian history also casts doubt on Popigai as an agency of
extinction.  Dyrosaurs were among the putative casualties of Popigai, but
here, as elsewhere, a biological explanation is better.
    Dyrosaurs were gavial-like, presumably fish-eating crocodilians.  They
had no African competitors in the Cretaceous, since the slender-snouted
Tomistomines were then confined to northern continents.  By the Eocene,
however, the Tomistomines entered Africa.  These crocs were so successful
there that their African descendents spread to Europe.  The obvious success
of the tomistomines in Africa, and the fact that they were gavial-like
fish-eaters, presumably competing for the same niche as the dyrosaurs, argues
that the latter were supplanted by competitors.  Potential physical factors
such as Popigai or cold are superfluous and dubious.
    Competition may better explain mammalian turnover and extinction as well.
 Another suggested victim of Popigai, Basilosaurus, was outlasted by more
modern whales.  Proboscidians, equines, etc. steadily progressed in the
Cenozoic.  If random physical factors were so important in extinction, and
biological factors so secondary, why are the derived forms often the only
survivors?  How could so much progress have occurred?
    Kelly Bell