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Re: (extinction) (long)



----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Saturday, July 06, 2002 11:26 PM

> 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.

Which is why I wrote "confirmed" and not "verified", as in sciences proving
is impossible. But unless there's another explanation for the totality of
the data, the whole K-T mass extinction, the above stands.

>  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).

Actually, I could almost get proud of how long I managed to keep Zhelestidae
out of this discussion. :-) There's a reason for my doing so: the JVP
abstract quoted in www.cmnh.org/dinoarch/2001May/msg00796.html. Looks like
they aren't ungulates or crown-group placentals at all, but instead close to
zalambdalestids (therefore I've mentioned them a few times as members of
that endemic Asian LK eutherian clade; that clade is called Asioryctitheria
if I correctly interpret the *Eomaia* paper which doesn't name it in its
cladogram).
        If I can take the abovementioned abstract as saying that zhelestids
had bunodont dentition (just like ourselves, right?), then they can hardly
have competed with the known K metatherians.
        The *Eomaia* paper, not citing that abstract, has found the
following topology for Eutheria:

--+--*Murtoilestes*
  |--*Prokennalestes*
  |--*Eomaia*
  `--+--*Montanalestes*
     |--Asioryctitheria
     |    |--*Ukhaatherium*
     |    |--*Asioryctes*
     |    |--*Kennalestes*
     |    `--*Zalambdalestes*
     `--+--*Daulestes*
        `--+--+--*Cimolestes* (Cimolesta)
           |  `--*Gypsonictops* (Leptictida)
           `--+--*Aspanlestes* ("Zhelestidae")
             `--+--*Eoungulatum* ("Zhelestidae")
                `--+--*Protungulatum* (er... Procreodi... see below)
                   `--*Erinaceus* (the recent hedgehog)

... in short, zhelestids (paraphyletic as usual) are not stem ungulates, but
stem placentals, stem boreoeutheres (confusing name) or stem laurasiatheres
according to this analysis. The authors lament that they didn't include
enough crown-group placentals to resolve placental relationships (the matrix
is already big enough, going down all the way to Tritylodontidae).

Exact tentative placement of *Protungulatum*:
www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Synapsida/E
utheria/Basal_Ungulata/procreodi.htm.

> And experts in the field have determined
> that they may have been competitors of marsupials.

Experts in the field have also determined that they may have been
competitors of herbivorous dinos. So... so I'm not sure what experts think
of this hypothesis today. Especially now that it's known what the Bug Creek
Anthills are.

> Archibald is strong on
> this: "[...] What is of interest is that the archaic ungulate invaders
> had dentitions very similar to contemporary

Puercan?

> 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_).

You know, I have the impression that Archibald gets more and more
catastrophistic with every paper...
The question in this particular case is when exactly "ungulates" appeared --
pretty early in the Paleocene, but how early, does someone know more?
(There's no question AFAIK that the metatherian extinctions happened right
at the K-T boundary, and that no "ungulates" were in NA before the K-T.)

> > > > 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.

And I answered that this is very weak evidence. Meanwhile I've sent links to
websites that explain why. -- Falconimorpha? Not another new name, please
:-)

> > 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?

1. I repeat the above -- I don't think you have offered reasons for this.
2. Sure. Of course. BOOM BANG FLOASH!!! The impact. I forgot the
"hypercane", the exorbitant winds produced by the hole in the atmosphere.
And then... too big to hide from fire and acid rain. Too great food
requirements for a Strangelove ocean and similarly sterile lands.

> > 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.

I know. I mean good enough competitors, better than what is in place.

>  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.

Still unlikely that they find such a lucky exaptation that offers such an
enormous advantage.

> 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.

1. Why should pterosaurs have been slower to take flight?
2. Why would that matter, what would matter wouldn't be the ability to flee
but the ability to defend the nest, right?
3. Wild speculation: Azhdarchids nested like megapodes -- the young hatched
and flew away. Very hard for a falconiform nest predator. There's absolutely
no evidence for this AFAIK, but is there any against it? :-)

> Birds, small, fast, and furtive,
> were better competitors in this predatory environment.

Which 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.

Then please suggest some structural constraints.