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Re: _Night Comes to the Cretaceous_



In a message dated 98-08-08 10:06:53 EDT, jbois@umd5.umd.edu writes:

<< No, but it makes it more probable that he will embrace an idea just
 because it is Alvarez that is thinking it.  Someone a little less
 comvinced of their own brilliance might expose any given idea to a little
 more scrutiny.  And that's the problem with the bolide-as-sufficient-idea,
 it does not withstand scrutiny (yet, anyway). >>

On the other hand, it could also be true that some paleontologists are
resistant to having a physicist step in and tell them the way things happened
at the K-T boundary, so they reach for ever more far-fetched alternatives to
the impact, when the correct explanation has been sitting under their noses
for the past two decades. This blade cuts both ways, I'm afraid, and doesn't
bring us closer to the truth.

<<But that's just it.  Measurement is difficult.  Taking Macleod et al 1997
The Cretaceous-Tertiary biotic transition. Journal of the geological
society, London, Vol154, 265-292  as gospel, the issue is still wide open.
This is true not only with vertebrates but with the entire biota.  Many
were going out in the Maastrichtian.  Often it was rare sp. that became
extinct.  Pseudo-extinctions (byproduct of adaptive radiations) are
confused with true extinctions.>>

What's a "pseudo-extinction"? Are all the organisms dead, or are they not?

<<  On and on.  They conclude: "Results
suggest that many faunal and floral groups (ostracods, bryozoa, ammonite,
cephalopods, bivalves archosaurs) were in decline throughout the latest
Maastrichtian while others (diatoms, radiolaria, benthic foramnifera,
brachiopods, gastropods, fish, amphibians, lepidosaurs, terrestrial
plants) passed through the K/T event horizon with only minor taxanomic
richness and/or diversity changes.">>

These data can be interpreted in any number of ways, depending on which theory
you care to support. For example, "in decline" doesn't mean "headed inexorably
toward extinction at the same time as lots of other species."

I suggest we begin at the other end: (1) There was a gigantic asteroid impact
exactly at the end of the Cretaceous; of this we are now certain. (2) A host
of Cretaceous organisms vanished at exactly the same time, or very shortly
after, all around the world. Duh!!

<<With archosaurs, birds, depending on how you feel about the timing of
modern the splitting of modern orders, seemed to sailed through the K/T
just fine.  Non-avian data is pathetically lacking.  But at the very least
it is not possible to determine whether there was a sudden or a gradual
extinction.  Knowing all this, it is jumping to conclusions to claim
preeminence for a single cause. >>

Most modern bird orders evolved during the early Cenozoic, quite likely in
adaptive radiations following the K-T event from a few randomly surviving
neornithan species. Enantiornithan birds didn't make it across the K-T
boundary, but fossils of these are still so abysmally rare that we really
can't conclude that they were wiped out by the impact.

The major issue of the K-T extinction is not the cause (asteroid impact) or
whether there >was< a mass extinction (there was); the major issues are which
organisms survived it, and why, and what happened to their descendands
afterward.