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Re: _Night Comes to the Cretaceous_ Ad Infintium



The problem here is one of resolution. Catastrpohic extinctions WILL look
like a gradual extinction if too "coarse" a scope is taken. In order to
regress the dangers of pseudo-extinction from the question at hand, simply
do not look at species level extinctions. Look at the number of familial and
genera represented before and after the extinction event. Individual species
evolve much more quickly than families and genera. It is unlikely that all
members of a family or genus would be caught in the middle of a speciation
event during anytime, never mind a mass extinction event.

Yes it is true that many taxa were in a decline during the late Cretaceous.
This decline, however, was in all likelihood, not significant enough to wipe
out whole families GLOBALLY! While replacement by "superior" taxa is an
attractive idea, it in not sufficient for reasons of ECOLOGICAL INERTIA.
Dinosaurs had already survived two MAJOR declines in their 200 million year
history and  weathered both events with a multitude of new species. (again,
stresses on a population tend TO increase genetic variability).

So far we have seen mentions of crocs vs amphibians (Lissamphibia) vs
mammals and birds,etc.... It HAS already been demonstated that differential
survivabilty has a very large bias towards animals that were/are memebers of
freshwater aquatic ecosystems. 51% of all families (55% of the genera)in
N.A. that have been associated with terrestial food chains were wiped out at
the K-T, whereas only 8% of families (26% of genera)from  freshwater aquatic
foodchains. Bony fishes, lissamphibia, turtles, and crocodylians show far
greater survivabilty than lizards, snakes, dinosaurs, and MAMMALS. In modern
ecology, it also well-understood, that freshwater aquatic biomes can recover
much more quickly than other ecosystems. Unfortunately, this particular
study (Garland Upchurch, 1989) does not include data from aquatic marine
biota.

Further....., there is DIRECT evidence of PRIMARY SUCCESSION across much of
this continent (from New Mexico to Saskachewan)- strangely enough, these
sediments are deposited directly on top of the layer containing the iridium
spike! Cretaceous indicator species, which made up 70-80% of the pollen and
spore fossil record, up to the iridium spike, then account for a mere 0-30%
of the pollen and spore fossil record. FERN spores rise sharply in the
fossil record (70%-100%), just as they do today. This fern spike persists
for the basalmost 15 cm of the Paleocene, followed by a decline to the
previous pre-KT levels, as ANGIOSPERMS regain their numbers. This was also
seen in the area surrounding MT. St. Helen following its last eruption.

Given that all animal life is dependent upon plant life, I would pay more
attention to the plant fossil record to determine what really happened to
different animal groups at the K-T.  If anyone is intersted, I have several
references on this subject and will be glad to send them off-list.

dlessin@accesschicago.net
david.lessin@Walgreens.com
David.Lessin@EMC.Walgreens.com

-----Original Message-----
From: John Bois <jbois@umd5.umd.edu>
To: Dinogeorge@aol.com <Dinogeorge@aol.com>
Cc: MICHAELS@preit.com <MICHAELS@preit.com>; dinosaur@usc.edu
<dinosaur@usc.edu>
Date: Saturday, August 08, 1998 2:06 PM
Subject: Re: _Night Comes to the Cretaceous_


>
>
>On Fri, 7 Aug 1998 Dinogeorge@aol.com wrote:
>
>> In a message dated 98-08-07 20:01:57 EDT, jbois@umd5.umd.edu writes:
>>
>> << From what I have read Alvarez suffers from a too facile assuredness of
his
>>  own opinions. >>
>>
>> Well, perhaps. But so what? Does this, by itself, make his opinions
wrong?
>
>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).
>
>> ... our available K-T-boundary
>> dinosaur samples suffer heavily from an indeterminable amount of
Signor-Lipps
>> effect, so just how less diverse--if this is in fact the case--is not
easily
>> measurable.
>
>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.  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."
>
>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.
>
>> Well, background extinctions have a multitude of contingent explanations,
of
>> course. Indeed, it is this fact that makes a mass extinction so strange:
How
>> could all those different extinctions, with all those different, complex
>> causes, just happen to coincide and line up so that the whole shooting
match,
>> on all continents everywhere at once, vanishes? I think it's even more
>> unlikely than that birds evolved flight from the ground up.
>
>You should be commended for looking beyond conventional explanations;
>suggesting viable alternate theories about bird phylogeny.  I ask you
>to consider that general acceptance of the bolide-as-sufficient idea is
>a restriction to deeper thinking inasmuch as it sucks up research dollars
>etc.  The point is the extinctions don't
>"line up".  Even Alvarez and co. talk about "stepped extinctions".  It's
>all in resolution.  From a distance it seems a single event.  But a closer
>look reveals a more complex picture. I would have thought _this_
>was common knowledge among those in the paleontological community.
>
>> Finally, where is it written that >all< extinctions must have a
complicated
>> explanation? Sometimes, I dare say, the explanation is >trivial<: the
earth
>> was smacked by a 15-mile-wide comet nucleus, and almost all the animals
and
>> plants were roasted. That's that. We're not explaining >all< extinctions
via
>> impacts, just one--the big one at the K-T boundary.
>
>If "almost all" animals and plants were roasted I would agree with you.
>But reality was much more complex.  And that tends to brand the
>bolide-as-sufficient idea as trivial!
>
>
>