Re: "Dinosaurs Died Within Hours After Asteroid Hit Earth..."

[David Marjanovic <david.marjanovic@gmx.at>]

> > *cough* deinonychosaurs *cough* oviraptorosaurs
> > *cough* segnosaurs ...
> >
> > Mickey Mortimer
>
> *Cough* Land-dwelling critters much LARGER than most
> birds.  VERY UNLIKELY to have been living in burrows.
> And, given the birds super-light construction, much
> heavier (thus requiring much more food by an even
> larger factor than did birds.)  Ever heard of "Occam's
> Razor"? *Cough*

So you agree that the feathers alone can't have been a reason? :-)

I think you overestimate the "super-light construction" of birds. They
aren't so much more pneumatic than an oviraptorosaur or dromaeosaur, and
have the added weight of flight muscles. *Bambiraptor* was quite small,
easily comparable to Presbyornithidae -- an anseriform group that survived.

I do think you're right that food has to do with the question. Segnosaurs
(as herbivores) and dromaeosaurs (as rather ordinary carnivores), at least,
were pretty directly dependent on green plant parts; the surviving bird
groups, as far as known, were not (galliforms can eat seeds, earthworms and
burrowing insects, anseriforms eat aquatic debris, the others I mentioned
eat fish which in turn eat aquatic debris...).

I recommend

Gregory J. Retallack: End-Cretaceous Acid Rain as a Selective Extinction
Mechanism between Birds and Dinosaurs, 35 -- 64 in Philip J. Currie, Eva B.
Koppelhus, Martin A. Shugar & Joanna L. Wright (eds): Feathered Dragons.
Studies on the Transition from Dinosaurs to Birds, Indiana University 2004

Abstract:

"Acid would have been a consequence of catastrophic events postulated for
the Cretaceous-Tertiary boundary: nitric acid from atmospheric shock by
bolides and from burning of trees; sulfuric acid from volcanic aerosols
[boo!] and from impact vaporization of evaporites; hydrochloric acid from
volcanic aerosols [boo!]; and carbonic acid from carbon dioxide of
volcanoes, fires, and methane-hydrate release. Pedoassays [erm... Greek:
pedon = soil] for buffering of soil acid above pH 4 are indicated by the
clayey, little-leached nature of latest Cretaceous and earliest Tertiary
paleosols in Montana. Chemoassay of 2.7 x 10^11 to 4.6 x 10^17 moles of acid
has been estimated from base-cation leaching of Cretaceous-Tertiary boundary
beds and paleosols in eastern Montana, and these estimates are compatible
with other independent chemoassays. Marine bioassay of pH suppression to no
less than 7.6, allowing survival of coccolithophores, foraminifera, and
dinoflagellates, requires a total acid load of less than 5 x 10^16 moles.
Similar limits come from a non-marine bioassay of pH suppression to less
than 5.5 but no less than pH 4, allowing survival of amphibians and fish,
but strong extinctions of non-marine mollusks in Montana. Acidification also
may have been responsible for heavy extinctions among evergreen angiosperms.
Vegetation browning would have been difficult for herbivorous dinosaurs and
their predators, but less problematic for small insectivorous and
detritivorous mammals and birds. Acid rain may have been an important agent
of selective mortality and extinction across the Cretaceous-Tertiary
boundary."