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RE: Tim's theory



        I'd like to disagree here in regards to evidence for a gradual 
extinction,
and the use of negative evidence to support your view.  First of all,
investigating biodiversity of fossil vertebrates is extremely suspect.
Compared with invertebrates or lower vertebrates, animals such as dinosaurs
are scarce in the Mesozoic ecosystem.  Furthermore, because of
preservational problems, they are even more rare as fossils.  The
Signor-Lipps Effect shows that the true temporal range of a species is not
known from fossil evidence when that species was fairly rare in the original
ecosystem to begin with (such as theropods).  Because we dont find them in
the fossil record very often, they may seem to go extinct at a certain time,
but this is probably not the true temporal range of the species.  Think of
all the dinosaurs where we only have one specimen.  Does this mean the
species only lived during this instant of time?  Of course not.  Thus, an
abrupt extinction can take on the signs of a gradual extinction in the
fossil record.
        The Deccan Traps fossil record also refutes a gradual extinction theory.
The Deccan traps are a series of many flood basalts with sedimentary
deposition (inter-trappean beds) in between.  If extinction was gradual, we
should see a decline in the abundance and diversity of dinosaurs through
each succeeding inter-trappean bed, even if it is skewed by the Signor-Lipps
Effect mentioned above. This does not happen.  One sees an abrupt
dissappearance of dinosaurs from the fossil records at the first Tertiary
inter-trappean bed.
        Using negative evidence is very suspect, especially when dealing with 
the
distant past.  We do not have a complete record of events, and just because
we dont have direct evidence for something happening doesnt mean it didnt
happen.  There may be problems with the Chicxulub Crater (I have doubts
about these studies though), however, that doesnt mean there wasnt another
impact that did cause the dinosaur extinction.  One needs positive evidence
for to support a hypothesis.
        On a final note, we know way too little about the effects of a major 
impact
to say what would or would not go extinct.

Regards,
Randall Irmis

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
KELL00BELL@aol.com
Sent: Monday, May 14, 2001 10:36 PM
To: dinosaur@usc.edu
Subject: Tim's theory


     David Marjanovic wanted me to continue this discussion onlist; so here
goes:

      Argentinosaurus was a Cenomanian sauropod, long predating T.rex.
Alamosaurus was the largest potential prey of the latter.  Perhaps it wasn't
even larger because available food was limited in northern regions where
ornithiscians were more important.
      Abelisaurs represented a lesser threat to sauropods than allosaurids
or tyrannosaurs.  Titanosaur armor probably would not have conferred
adequate
protection from T.rex (I consider Upchurch's article flawed, but that's a
different story.)
      The best estimate for the age of the Nemegt is about mid-Maastrichtian
c. 69Ma.  I discern about four lines of evidence for that.  Some data hints
at gradual extinction caused by T.bataar--perhaps the subject of a later
post.
      Maybe the regression had progressed farther by K-T time than at 68 Ma.
 Pararhabdodon endured climatic change, but its extinction could have been
rather abrupt if T.rex ever gained access to Europe--so abrupt the
preservation of tyrannosaur remains would probably be unlikely.  There is
clear evidence that tyrannosaurs could traverse marine barriers and may have
entered e. America, even Europe, around K-T time (later post.)
      In fact, there is no clear correlation between impacts and extinction.
 Frankel admitted as much with regard to Manicouagan.  Consider also the
double Kara impact 73-76 Ma (which may have been a triple impact if it
coincided with Manson 74Ma.)  Dinosaurian diversity actually peaked around
then, even though the two Karas (65 km and 25-70 km) amounted to a major
event.
      Russell thinks the Manson impact decimated North American dinosaurs,
their places taken by Asian immigrants.  There was, however, nothing in Asia
comparable to Pentaceratops.  Ceratopsids, etc. were clearly unscathed,
despite their close proximity to the blast.
      Prior to the K-T, there was no major Lk extinction event in North
America until c. 68 Ma, when saurolophines, centrosaurines and lambeosaurs
vanished.  No known impact coincided with this event, and even if one did,
why would it spare Edmontosaurus and chasmosaurines?
      Frankel says multiple impacts caused the Late Jurassic "mass
extinction."  What "mass extinction" ?  Stegosaurs survived into the Early
Cretaceous, and sauropods were slow to relinquish their ecologically
prominent role.  In Gondwana they remained dominant to the end even though a
putative cause of their decline--Morokweng--is in South Africa.
      Even if Manicouagan DID coincide with the end-Triassic die-off, does
it really account for the data?  Why would the largest animals, the
dinosaurs, survive?  Likewise, why did Popigai/Chesapeake kill off certain
rodents, carnivores and reptiles, supposedly, while larger rhinos,
elephants,
etc. survived?  Isn't that contrary to what is predicted by impact theory?
      Frankel addressed some of Officer's arguments, notably the latter's
very poor case for gradual extinction.  I noticed he didn't mention the
report of 350m of undisturbed Campano-Maastrichtian sediments overlying the
Chicxulub melt, nor the claim that the K-T age for Chicxulub is erroneous,
just like initial reported K-T age for Manson.
      Based on the low irridium content of Deccan, etc, basalts Frankel
rejects a volcanic source for K-T irridium, saying millions of eruptions
would have been required to produce it.  Zoller, however, reported in effect
that the concentration of irridium in airborne volcanic particles was four
orders of magnitude higher than that in basalts.  On that basis, the number
of required eruptions could have been four orders of magnitude smaller i.e.
not millions but hundreds (it seems odd that a body as massive as Earth
can't
compete with a tiny asteroid as a source of irridium.)  Perhaps the K-T
event
coincided with intense volcanism (average one big eruption every other year
for a millenium?)  This would not have doomed the dinosaurs directly;
Frankel was right to note the benign nature of Deccan eruptions.  Intense
volcanism nevertheless could have signalled an acceleration of the Laramide
revolution, or rising of the land, increasing the scope of tyrannosaurid
depredations while diminishing the habitat of sea reptiles, thus
simultaneously ending the Mesozoic on land and at sea.
      We could argue interminiably about putative impact evidence, land
links, etc.  What ultimately matters most is this: What PREDICTIONS does my
theory and the asteroid theory make, with regard to the pattern of survival
and extinction across the K-T, and which predictions are best confirmed by
the evidence?  A theory which attributes extinction to tyrannosaurs makes a
very obvious prediction: the survival of taxa beyond their reach e.g. birds,
which could fly away and next in trees, mammals, which were nocturnal,
burrowing or arboreal, and freshwater creatures which were also generally
safe.  Of course, the prediction of their survival is confirmed.  In
contrast, the asteroid theory rather poorly predicts what is observed.
Frankel mentioned oven-like temperatures followed by darkness and cold.  The
former should have wiped out life far more indiscriminately.  Birds should
have been just as vulnerable as dinosaurs.  Arboreal mammals, etc. should
have gone up in smoke with the trees.  Severe cold and darkness should have
devastated the reptiles, especially crocodiles, but the latter survived even
at fairly high latitude.
      All things considered, the asteroid theory is greatly overrated and
there should be greater receptiveness to alternative hypotheses.