K-T calamities

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Lest we forget, the impact winter is not the only environmental
perturbation that organismal populations would have had to deal with. Acid
rain (according to some scenarios think of automobile battery acid falling
out of the sky) and global wildfires (by some accounts much of North
America was burned to the ground) would also have played a role. So, in
Neale's intriguing image, take that hedgehog (or beetle), dunk him in
battery acid, then throw him on the barbie for (at least) a few hours, and
then into the 'fridge for (at least) several months. For plants, add (at
least) several months of twilight-levels of light penetration during the
"day."

Note also that if the June impact time is correct (Jack Wolfe's got at
least a 1/12 chance of being right) this means that there would have been
no summer that year (assuming the proximate effects lasted for only a few
months) and that the winter would in all likelihood have been anomalously
intense. Most papers dealing with the physical results of an impact argue
that these effects would have played out over years, not months.

Given this very approximate picture of a post-impact world we might ask
whether the known pattern of terrestrial extinction and survivorship makes
sense. Certainly the above scenario calls for extinctions to occur. But I
think we should be trying for an explanation that says a bit more than "the
K-T impact killed all the species all over the world, except for the ones
it didn't kill." Dave Archibald has asked and provided preliminary answers
to the question of comparing predictions and extinction patterns in a
couple of recent publications.

Archibald, J. D. 1996. Dinosaur extinction and the end of an era: what the
fossils say. Columbia University Press, New York.

Archibald, J. D., 1996. Testing extinction theories at the
Cretaceous-Tertiary boundary using the vertebrate fossil record. In:
MacLeod, N. & Keller, G. eds., The Cretaceous-Tertiary mass extinction:
biotic and environmental changes. W. W. Norton & Co., New York, 373-398.

I won't steal Dave's thunder by giving away his conclusions, but his
analytical design and his results make very interesting reading. It is to
these types of studies that we must turn to decide what role the K-T
impact(s) may have played in the Late Cretaceous faunal transition. Even
almost 20 years into this controversy, we've hardly scratched the surface
of testing the biotic predictions of the various impact scenarios in any
sort of detail. As the "K-T insect" string makes perfectly clear, there
still a lot to be done in this area.


Norm MacLeod





___________________________________________________________________

Dr. Norman MacLeod
Micropalaeontological Research
N.MacLeod@nhm.ac.uk (E-mail)

Department of Palaeontology, The Natural History Museum,
Cromwell Road, London, SW7 5BD

Office Phone: 0171-938-9006
Dept. FAX: 0171-938-9277
E-mail: N.MacLeod@nhm.ac.uk
___________________________________________________________________