Re: Extinction

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

On Sat, 25 Mar 2000, Tommy Tyrberg wrote:

> Do You mean that You can think of a scenario where a large asteroid impact
> on a continental shelf can occur *without* having the effects I mention? If
> so I would be interested in details (You can skip the carbon dioxide and
> sulfur dioxide since they are dependent on the geology of the impact area,
> though the geology is right at Chicxulub).

I simply distrust our ability to know exactly what happened.  I'm
skeptical.  The window of destruction seems very small (i.e., non-avians
only, going out completely) and precise that I don't believe we can say
that it was such an indiscriminant killer.

> >Such a claim suggests,
> >a) enantiornithines could not compete in the shorebird niche (but we know
> >they were a diverse taxon); or, b) the asteroid had smart-bomb
> >capability.
> >
> No, I don't think only a few shorebirds survived. But I do think that the
> present-day avifauna is derived from a quite limited number of late
> Cretaceous species. And it is a fact that enantiornithines are strikingly
> rare (but not quite absent) in coastal and marine environments.

Isn't it true they were vanishingly scarce everywhere in the years
(?) before the K/T?

> >The Western Interior seaway drained thus taking away a huge area of
> >coastal plain.
> >
> Yes, but there would still be large areas of coastal plains left arond the
> periphery of the continent.

True.  But most (all) North American fossil sites are inland.

> Also dinosaurs did live inland in upland areas
> (like in Mongolia). Also note that dinosaurs did survive for at least
> several tens of millions of years (until the Maastrichtian) in India and
> Madagascar and on New Zealand showing that they did not require
> continental-size landmasses for long-term survival.

Right.  But I don't think we know when dinosaurs became extinct in those
places, do we?

> Since I happen to have field experience of all extant ratites (except Dwarf
> Cassowary) I know that this is simply not true. A quick summary of habitat
> preferences:
> 
> Ostrich: avoids closed forest, otherwise almost ubiquitous. I've seen it
> (breeding) in e. g. mopane woodland, dense acacia woodland, fairly extreme
> desert and coastal fynbos.

Answered in seperate response.