RE: Hell Creek (long)

["Steve Brusatte" <dinoland@lycos.com>]

On Sun, 2 Jun 2002 05:24:12   
 Allan Edels wrote:
>Concerning the Oxygen levels found in amber:  When I first heard of
>this, it seemed to be THE ANSWER - something big hit the earth and
>ruined the atmosphere!  The change would have been sudden. The numbers
>I've quoted were from an article in the Dino Fest 1996 Symposium
>publication (published for the 1998 symposium).  (If someone needs the
>ref, I'll try to dig it up).  

I believe it was a paper by Richard Hengst, correct?

>Tommy Tyrberg said: " Extant animals certainly have a fairly
>high tolerance in this respect... Birds are _incredibly_ tolerant ..."
>While extant animals can handle lower O2 levels - THAT'S THE POINT.
>Those that COULDN'T handle the change DID NOT SURVIVE THE K-T.  (Note
>that according to the Amber bubbles, mid-Miocene mammals (etc.) survived
>an O2 level as low as 14%).   

Although, as you mention, the amber evidence isn't very reliable, let's assume 
that oxygen levels did indeed drop off.  Would this really have had anything to 
do with the KT extinction?  Osteological evidence shows that at least some 
nonavian dinosaurs possessed more birdlike respiratory systems.  Based on 
respiratory systems seen in extant birds, these dinosaurs would have likely 
been able to survive a drop in oxygen.  Plus, what about the myriad birds that 
went extinct?  How can modern birds breathe and function at heights several 
miles above the ground while LK birds, which likely had similar respiratory 
systems, couldn't handle an oxygen drop?  It doesn't make much sense to me.

>Before everyone starts yelling "What about the small pterosaurs? What
>about the [fill in your favorite small dino]?"  - Consider this: There
>are extant animals today who will die if they cannot have a specific
>food to eat (e.g. Pandas - bamboo, Koalas - eucalyptus, etc.).  We don't
>know how well a pterosaur would fair if the only fish that it eats were
>all dead, with no replacements. With major groups of animals killed off
>by the other effects of the bolide impact (and "collateral damage"),
>some animals would go extinct due to their only food source
>disappearing.

Most of the pterosaurs left near the KT boundary, AFAIK, were generally much 
larger forms.  There might have been some smaller forms that still existed, but 
by the closing of the Cretaceous the pterosaur lineage had become very 
specialized, possibly due to competition from birds.  Who knows.  But, if true, 
the increased specialization was a more likely explanation for pterosaur 
extinction, as becoming larger and ultra specialized does not generally bode 
well for survival.

>Last piece of this post: Concerning the sulfuric acid creation in the
>upper atmosphere - If acid rain did occur (as seems likely), then how
>much would it affect the preservation of fossils.  Is it possible that
>there was enough acid rain to account for the lack of fossils prior to
>the K-T (i.e. the acid rain sufficiently changed the soils, that no
>(major) fossils were preserved in the underlying layers).

It could have not only affected fossilization, but also destroyed recently 
created fossils.  I don't know if this has been specifically tested in the 
laboratory, though.  Refs?

Steve

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