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Re: (extinction) (fwd)



David said:

> First, we have that impact. _All_ of the above effects
> are expected to result from such a big impact, and together they are
> expected to produce a mass extinction. And yabbadabbadoo, a mass
extinction
> is just what we _happen_ to find right at the time when the bolide
impacted.
> Prediction confirmed. :-)

No doubt.  But a prediction doth not a theory make.  A confirmed prediction
of the geocentric universe is that the sun will rise on one horizon and set
on the opposite horizon.

>...I can remember only one "ungulate" as having been proposed
> to be K in age, *Protungulatum*, so presently "the true diversity of
> condylarths" at the K-T looks pretty similar to 0. I also don't understand
> why such an animal would compete with the known Hell Creek metatherians,
all
> of which seem to have been (AFAIK) insectivores or specialized carnivores,
> not generalized omnivores, let alone herbivores.

 Evidence for "rooting the ungulate radiation" earlier than K/T is found in
85 Ma sediments of Western Asia (Archibald, J.D., 1996 Fossil Evidencve for
a Late Cretaceous Origin of "Hoofed" Mammals. Science 272 1150-1153). Their
descendants were on the scene in NA either right at or just after the K/T
boundary and subsequently in SA.  The point is, they were around and doing
things--immigrating, evolving.  And experts in the field have determined
that they may have been competitors of marsupials.  Archibald is strong on
this: "Our best guess now is that the lineage that gave rise to these
mammals first appeared in Middle Asia between approximately 80 and 85
million years ago and reached North America near the K/T boundary.  What is
of interest is that the archaic ungulate invaders had dentitions very
similar to contemporary marsupials and presumably ate similar things.  It
seems more than coincidence that marsupials did well in North America for
approximately 20 million years only to almost disappear with the appearance
of the ungulate clade." (from his"Extinction" article in _Encyclopedia of
Dinosaurs_).


> > > What on Earth (or elsewhere!) can compete with *Quetzalcoatlus*???
> >
> > Falconimorphs eat Q babies.
>
> Evidence for K falconiforms?

I wrote a post a while ago about molecular finding that falcons and hawks (I
think) had a common ancestor pre-K/T.  If true this suggests the presence of
the raptor bauplan.

> Evidence that azhdarchid extinction happened at
> different times in different places?  Evidence that azhdarchids were
totally
> unable to do anything against a flying nest predator?

Reasons why a diverse and widespread clade would quietly cash it in?

> They can't be better competitors when they are just starting to _become_
> competitors. An example of "evolving into an occupied niche" would be if a
> new clade of gnawing mammals would be evolving from shrews right now. That
> won't happen: as long as that process isn't finished (at least), the
> existing rodents are much better competitors.

Species never are perfect competitors.  It's always more complex.  They
compete perhaps in one niche dimension--but this may be enough to put the
other species out of business.  If my guess/hypothesis/rabid speculation for
pterosaur extinction is right, it happened like this: birds and pterosaurs
competed for food, nest sites.  Pterosaurs had the edge because they were
bigger, tougher, and gosh darn' it they deserved it.  But then a
falconimorph preyed on pterosaur babies.  It could do this because
pterosaurs were more conspicuous, slower to take flight than birds.  Birds,
small, fast, and furtive, were better competitors in this predatory
environment.

> > I'm not suggesting anything fantastic here--just an
> > effective predator on pterosaur chicks at all locations.
>
> I do think that this is rather fantastic. Why would not one pterosaur
> population evolve something, some behavior, against that, when the
selective
> pressure to do so is greatest?

Here you may be up against absolute limits in structural design.  Come to
think of it, good reason to go extinct.