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Re: "But What About The..." arguments (now rather short!)
On Thu, 6 Jun 2002, David Marjanovic wrote:
> > Things the bolide "null" hypothesis has yet to refute: Neornithine birds
> > outcompeted enantiornithine birds;
> First I'd like to have some evidence that they did, and a hypothesis about
> how they possibly did it.
Evidence is enantis disappear and neos diversify. Note: this is the same
evidence for your preferred hypothesis. But mine is more parsimonious
since, a) competition/predation are observable phenomena and are in
operation today; and 2) the mechanism proposed for bolide-induced enanti
extinction requires a lot of angels dancing on pins, viz., enantis and
neos--both perfectly capable of dispersal (one would expect)--have to be
hermetically sealed in seperate hemispheres, i.e., neos only in the
south. This is a stretch compared with my relatively simple
hypothesis. If neos did ascend via competition, myriad possibilities
exist for how, including: behavioral advances, reproductive advances,
flight characteristic advances, etc., etc.
> > marsupial extinctions were due to
> > competition/predation from eutherian invaders;
> Metatheria and Eutheria coexisted from their divergence early in the K to
> the K-T throughout Asiamerica; after it Eutheria diversified, while
> Metatheria hardly did -- but it held on far into the Miocene throughout
> Laurasia. Metatheria lost much of its diversity at the K-T, so probably did
> Eutheria, but its fossil record is even worse.
OK. But replacement by invaders is documented in Van Valen paper of
60's. (ref. if needed). All sorts of reasons why marsupials may have
fared better in some places rather than others...the main point here is
that the marsupial extinctions in NA already have a culprit which does not
> > pterosaurs were barely
> > hanging on (i.e., diversity was lowest ever _before_ K/T);
> Given the few presently known fossils, I'll believe that their diversity in
> the Maastrichtian was the lowest ever; but I'm not sure I'd call the 3
> biggest flying animals ever "barely hanging on". I also don't know how old
> things like *Ornithostoma* are.
But the disappearance of smaller forms is _very_ important. Creatures
don't just surrender niches. The smaller forms were kicked out. Birds
must be prime suspect. Again, bolide not a player.
> > some non-avian dinosaurs lived past the K/T and should have
> > had to re-establish populations.
> I do think most surviving non-neornithean dinos would have re-established
> populations that would subsequently have diversified. That the latter didn't
> happen is IMHO good evidence that the rest didn't happen either. I'll look
> up the paper on the supposedly Paleocene dinos of India, which is the only
> case I don't know a refutation for.
Have we finished with the eggs in China, and the hadrosaur bone in SW
NA? By the way, if it's the paper I've been talking about (Bajpai
and Prasad 2000) they're not saying therapod bones are Paleocene--since
they were found with Late K ostracods--they are saying that the teeth,
are above the iridium layer. Anyway, we have found bones so close to the
boundary, Signor Lipps says their existence in P. is a cinch.
> > I'm sure there are others.
> I'm not urging you. But if you can find some, please tell me sometime.
Absence of drastic teleost extinctions; spotty angiosperm extinctions
(i.e., local effects); low and declining diversity of ammonites and their
turtle friends; possible disappearance of smaller dinos; slight relaxation
in size constraints for pre-K/T mammals (in NA, at least); failure of
dinosaurs to re-establish dominance in post-K/T world (i.e., other species
make life for otherwise fab body plan miserable--this may provide an
inference for pre-K/T dinos especially if bird and mammal hypos pan
out)...I'm sure there are others :-)