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Re: Dinosaur Extinction (Again)



On Fri, 22 Nov 1996, Thomas R. Holtz, Jr. wrote:

> Actually, the marine extinctions seem to make a lot of sense from
> the bottom of the food chain up.  There is massive extinction among
> the coccolithophorids (nanoscopic algae, whose calcareous shells
> make up the sort of limestone called "chalk"), although a few
> lineages survived.  The most conspicuous die offs among the
> macroinvertebrates are from probable planktonivores: ammonites (see
> work by Seilacher suggesting that these guys, unlike the nautiloid
> and coleoid cousins, were plankton-eaters), rudists, inoceramids (if
> any lived to the end of the Maastrichtian), etc.  At least some of
> the marine reptiles that died off, mosasaurs in particular, were in
> part ammonite eaters (evidenced by mosasaur bites on ammonites).

        A catchy term for this, as opposed to "top down" would be "bottom 
out". One notable trend is the survival of organisms associated with the 
freshwater ecosystem. Why? One idea I heard was that it could subsist on 
detritus if there were no photosynthesis. Perhaps the water moderated the 
cold? The whole dust-in-the-sky thing sounds good when you compare 
Pinatubo (1 degree C drop in that years temperature) with something the 
size of Chicxulub, but the dust drops out pretty fast. 
        A thought- perhaps 
we're not thinking catastrophic _enough_. Maybe the damage was done in a 
year and from then on the ecosystem exploded kind of the way a place like 
Mt. Saint Helens (frogs survived through that, incidentally. I don't 
think Bakker was pleased when I mentioned that to him) or Krakatau does 
after being just wailed on. But by this time, our damage would have been 
done and while some taxa that survived (say 99% mortality) would 
proliferate, others (w approx 100% mortality) would see the return of 
semi-normal temperatures far too late... Of course an event like this 
would wreak havoc with the weather for years to come even if normal 
temperatures returned fairly quickly. And of course the sunsets, at least 
for a while, would have been *very* pretty after Chicxulub.

        Who knows. Other 
asteroids hit, but don't seem to have caused this kind of calamity. The 
Permian is still open but the Sci. Am. article I saw had the author- who 
had been a longtime gradualist- claiming that the Permian event was much 
more rapid than had been previously thought. He was still talking about a 
million years or so, but he was taking an increasingly catastrophic view 
of it. INSECT orders disappeared in the Permian. That 
gives you a clue of the kind of severity we're talking about (BTW add the 
common cokroach to your list of bipeds, supposedly they can run on their 
hind legs) but there's really not much evidence for a bolide.