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Re: _Night Comes to the Cretaceous_



In a message dated 98-08-09 02:25:04 EDT, jbois@umd5.umd.edu writes:

<< On Sat, 8 Aug 1998 Dinogeorge@aol.com wrote:
 
 > 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.
 
 In my experience paleontologists are very wary of accepting explanations.
This is reasonable since it is hard to test historical hypotheses.  Most seem
content to speak the truth, which is in this case: "we may never know".>>

HOOBOY what a load this posting is! Where oh where shall I begin??

In reply to the above--paleontologists "may never know" about the cause of the
K-T extinction, but pretty much the rest of the scientific world does! I will
surely agree that much of the time, "may never know" is indeed the case in
matters paleontological. Such as whether or not dinosaurs were endotherms. But
with the K-T event--given that there's a >known< asteroid impact, crater and
all, associated >exactly< with a mass extinction, so that the >actual physical
residue< of the asteroid is preserved and >cuts across the faunal K-T
boundary<, and that lots of species below the residue do >not< appear above
it--well, frankly, you don't have to be a rocket scientist, if you know what I
mean.

<< > What's a "pseudo-extinction"? Are all the organisms dead, or are they
not?
 
 When one species evolves into another, the ancestor species ceases to
 exist.  This is a pseudo extinction.  >>

This isn't any kind of extinction, unless ordinary death is to be classed as
extinction; this is >anagenetic evolution<. "Pseudo extinction" indeed.

<< For example, according to David Archibald: "During the Latest Cretaceous
 and the Paleocene in Western North America, disappearance rates for
 mammalian genera track appearance rates, both reaching their peak in the
 early Paleocene following the extinction of non-avian dinosaurs.  Some of
 the disappearances during this time were pseudo extinctions that resulted
 when ancestral species disappeared during speciation.">>

I'd like to see Dave Archibald (or anyone else) demonstrate that any so-called
pseudo extinctions as described herein actually took place. He'll have every
cladist down his throat in no time. Where's Wagner when you need him?
 
<< In this way a creative bout of adaptive radiation can look like a mass
extinction! >>

Balderdash. And I suppose black is just a rather dark shade of white, eh?
  
<< > 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!!
 
But I've already said that Alvarez is talking about "stepped extinctions".  A
host of organisms did _not_ vanish at exactly the same time.  By starting at
the other end you've got ot backwards.  You have an "event" and you are trying
to shoe-horn all the data into an instant of time.  The best evidence we have
suggests this is not what happened. Merely repeating it over and again doesn't
make it true.   >>

There is presently >no way< to distinguish between Signor-Lipps effect and so-
called "stepped extinction." And, how convenient that all these "stepped"
extinctions come to a climax >at exactly the time when the asteroid hits<.
Smells too fishy to me.

The most detailed surveys of the late Maastrichtian find evidence of dinosaurs
up to within about 60 cm of the K-T boundary, and there are plenty of reworked
dinosaur fossils in early Paleocene deposits. That's close enough to the K-T
boundary for me.

<< > 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. 
 
 This is unsupported by anything but negative evidence.  It's  simply too
 early to tell if whether molecular clock data is right when it says
 most orders evolved _before_ the K/T!  if birds exhibited mass-survival
 over the K/T, wouldn't this falsify the bolide-as-sufficient idea?  >>

Even if lots of birds survived the asteroid impact, which I doubt, it wouldn't
matter at all. So the impact missed the birds; it got the dinosaurs and a
bunch of other animals and plants.
 
<< > 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.
 
 But even Feduccia recognizes a gradual decline in enantiornithan birds
 over the end of the Cretaceous.>>

Maybe there was, and maybe there wasn't. Enantiornithans are generally so rare
as fossils that there don't even have to be any in the Maastrichtian at all to
suspect a Signor-Lipps effect. The important thing is not that there was a
decline; the important thing is that there aren't any enantiornithans known
above the K-T boundary, and there are enantiornithans known from below the K-T
boundary. So they're certainly >candidates< for extinction as a result of 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.
 
 Unless you can explain survival as well as extinction, you don't have an
 explanation for extinction!  The bolide-as-sufficient idea does not
 explain either the timing or the pattern of extinction and survival.  As
 such, it was an event, that's it. >>

Then it's the greatest coincidence of all time! Just as all those dinosaurs
and other Mesozoic creatures went mass-extinct, for a thousand different
reasons, bam!, the asteroid hit. An asteroid fully capable of wreaking
tremendous havoc on the entire planet's biosphere.

What you're trying to tell me goes something like this: A gunman opens fire at
a group of ten bystanders. Say three persons survive. Nobody sees the actual
shooting, and the three survivors are badly wounded and too incoherent to
serve as witnesses. The other seven bystanders have their bodies riddled with
bullets. Now, you're telling me that >because there were three survivors<, the
gunman cannot have killed >anyone<: that because the bullets were ineffective
against three survivors,  the bullets couldn't have created the seven corpses,
either. Rather, all those dead bystanders coincidentally died of heart
failure, or malaria, or a particularly virulent strain of smallpox that they
all just caught from one another, or something else as yet unknown, just
before the bullets hit their bodies. Well, this is certainly light-years
beyond parsimony!

As a corollary of my gunman and bystanders example, you >don't have to explain
survival<. You are only obliged to explain extinction. If you feel like
searching for why one or another group managed to survive the impact, be my
guest, but you'll just end up going around in circles, waving your hands at
one untestable hypothesis after another.