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Re: Selective Extinction

> From: Chris Campbell <sankarah@ou.edu>
> Rob Meyerson wrote:
> > Betty Cunningham writes,
> > >birds, of course, survived, whereas pterasauroids did not so if you
> > >perhaps explain why?
> > >Wehn Mt. St. Helens went off, birds that flew away survived, but still
> > >had to deal with the ash that covered everything afterwards to search
> > >for food and water.
> > 
> > When we look at the major theories for the late-K mass extinction, all 
> >of them point to a heavily restrictive environment.  To use the
> >impact scenario as an example, the resulting disruption of the land food

> >chain will mean that food will be in short supply.  Because of this, 
> >animals that can get by on small amounts of food will survive, which
> >include most ectotherms and smaller endotherms.  Under this hypothesis, 
> >birds survived because they enhabited the "small endotherm" end of the 
> >scale, while the pterosaurs were in the "large endotherm" end.
> > 
> > So, IMHO, birds survived simply because they were small.
> Problem being that crocs (large ectotherms) survived while small dinos
> (small endotherms) didn't.  
> Chris

But just how small were the smallest adult dinosaurs at the <very end> of
the Cretaceous?  I have heard _Velociraptor_ described as being
coyote-sized; small in terms of non-avian dinosaurs, yes, but still more
needy (from the standpoint of dietary and environmental requirements) than
the minuscule mammals with whom they coexisted.  As I understand it, the
very largest of the Mesozoic mammals was the size of a raccoon, but most
were more comparable to the size of extant shrews and mice.  Burrowing or
arboreal, nocturnal lifestyles have been proposed for Mesozoic mammals, and
it is believed that many occupied niches similar to those of modern rodents
or insectivores.  This profile would appear to have been most unlike that
of the non-avian dinosaurs of their time (whether they were endothermic or
not).  And let's not forget that the marsupials were apparently hit pretty
hard around the KT boundary, too, except in South America.  Still, I would
be interested to hear evidence of minute adult dinosaur groups which were
snuffed out during the great extinction event, or of large mammals which
made it across the apocalypse unscathed.

Crocs are another case, too, due to their primarily aquatic lifestyle. 
Fresh water fish, amphibians and turtles seem to have also managed quite
well.  Were the first surviving crocodilians large or small species?

We will be better equipped to understand this extinction event if more
sites are discovered around the world which contain a good fossil record of
what was going on before, during, and after the extinctions.  It may be
that the "patterns" we note at this time will be called into question as
more data become available.  And the full richness of the puzzle may never
be fully grasped, because the fossil record gives us insufficient
information regarding the many ways in which species of Mesozoic plants and
animals depended upon one another.  We are so ignorant of such interactions
as they occur today that scientists are hard pressed to explain extinctions
going on under our very noses.  _The End of Science_?  I think not.

Ralph Miller III <gbabcock@best.com>

"Sometimes ya just gotta hunker down like a mule in a hailstorm."