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Night Comes to the Extinction Problem



In a message dated 98-08-19 21:01:52 EDT, jbois@umd5.umd.edu writes:

<< Just a reminder to those using Horner's passenger pigeon analogy.  Horner
 is saying that various causes have withered down non-avian dinosaurs to
 the point of extinction.  And the last passenger pigeon's killer is the
 _bolide_. >>

Horner also said that he didn't care how they died; he was more interested in
how dinosaurs >lived<.

I've surveyed the same literature that Jack Horner has surveyed, and I don't
see the dinosaurs as being anything like on the verge of >simultaneous
extinction< exactly at the end of the Maastrichtian. Their diversity was a tad
low, perhaps (or is this just Signor-Lipps effect?), and they were losing, or
had pretty much lost, their non-avian evolutionary engine--the small, rapidly
evolving forms that produced the larger, more slowly evolving forms--to steady
competition from the mammalian evolutionary engine. But none of this mandates
death at the K-T boundary. Had there been no impact, large herbivorous
dinosaurs might >gradually< have been replaced by large mammals during the
Cenozoic (actually, there wouldn't have been a Cenozoic--just a continuation
of the Mesozoic), although I think that persistent lineages of giant,
flightless birds--the "avian" theropod equivalents--could well have kept
mammals from exploiting large-animal niches for quite some time.

Having said this, let me now note that I've just deleted something like a
hundred e-mail posts on the extinction problem from my Personal Filing
Cabinet. I think this thread has run its course, and then some. I certainly
have nothing more to say on the extinction problem, and reading those endless
posts on the subject has convinced me that nobody else does, either. Without
the invention of a time machine, we'll never >know< what really happened at
the K-T boundary. We know there was an impact, but did it kill the dinosaurs?
I think so, but >proving< this impossible. We weren't there, and not nearly
enough data have survived the 65 million years since to allow us to
distinguish among all the possibilities and to sift out the wrong hypotheses
from the right. All arguments and discussions, regardless of novel insights,
eventually conclude by bashing themselves perpetually against the Wailing Wall
of time.