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Re: (extinction)



----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Friday, July 05, 2002 4:17 AM

> On Thu, 4 Jul 2002, David Marjanovic wrote:
>
> > Just to make sure... not one "diffuse agent", but _all of them at once_
> > respectively following each other: plasma shockwave AND earthquake
between
> > 10 and 13 on the Richter scale AND ejecta raining down AND global
wildfires
> > AND soot AND nitric oxides AND impact winter AND acid rain AND
greenhouse
> > effect.
>
> In other words: whatever it takes to knock everything off, that must have
> been what happened.

The other way around: 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. :-)
(I'm deliberately portraying it differently from how the historical process
of discovery took place.)

> > What about: Almost all mammals were killed. [...] For a clade to
> > survive, it's enough, as has been pointed out many times onlist, that
one
> > single viable population survives, whatever more there was can be killed
> > off.
>
> I just don't see that this is the case in the western NA interior (the
> most studied).

Other people seem to do so, however.
www.dinosauria.com/jdp/misc/hellcreek.html#mammals lists only leptictids
(*Gypsonictops*) and cimolestans (*Cimolestes*, *Batodon*) as eutherians
from the Hell Creek Fm. These groups continue into the Puercan, but lots and
lots more are present then with them (arctocyonians, plesiadapiforms etc.).

> At the very least there must have been considerable
> diversity among placentals to foster the almost instant
> diversification.  Did this happen before, or immediately after the
> K/T.  Not sure.

The abovementioned list implies immediately after it. From the fossils (and
not the molecular clock estimates), it looks like the Paleocene explosion of
mammals was real rather than a drawn-out affair over the whole K.
www.nceas.ucsb.edu/~alroy/Paleocene.html discusses at length how good the
fossil record is. :-)

> "because the true diversity of marsupials and condylarths
> (at the K/T in W. Int. NA) remains unknown, we cannot evaluate
> the extensiveness of competition, if any...It would be premature,
> therefote, to boast competitive dominion (of placentals)(at that
> time)."

I agree. However, 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.

> If I understand your point, you are saying that because
> marsupials remained at other locations, that placentals probably didn't
> outcompete marsupials at this location.

That's not my entire point. My point is that
-- no gradual increase in eu- and no gradual decrease in metatherian
diversity is seen
-- when placentals immigrated from Asia, why are none found in Asia in the K
-- when placentals were superior to NA metatherians, but not to Asian
metatherians, why didn't the latter come with them to NA

A way around the second argument could be that no end-Maastrichtian layers
are known from Asia in the first place. But far too little is lacking for

> Also, see http://www.concentric.net/~Ewdewar/research/SVP97/ for
> interesting discussion of dietary diversity at Puercan 1.

Indeed interesting, but IMHO of no relevance to the K.

> > I wouldn't be surprised if an enantiornithean would turn up in
Maastrichtian
> > layers of Antarctica that have so far only yielded Neornithes, except
for a
> > scrap of ichthyornithiform I've occasionally read about. Imagine: 100 %
of
> > all birds north of Antarctica go up in flames. 99 % of those in
Antarctica
> > do likewise. These include 100 % of enantis, 100 % of ichthyornithiforms
and
> > 99 % of neornithean _species_. How does that sound? :-)
>
> It sounds circular!  You're finding ways to make it happen--because it
> happened.

What's wrong with that? Don't I show that mass extinction is _not
in_compatible with neornithean survival? :-)

> Yes, it might have happened that way--or--it might have been
> competition.  No way to tell, _unless_ you already know that the bolide
> did it.

Another method is to falsify the competition hypothesis (and all other
putative alternatives). Unfortunately, this is presently not possible,
because the competition _speculation_ is not built on much evidence to date.

> I think it's better to say (as HP Habib did) that the bolide may
> have had a role in determining which clade was the better competitor.

Maybe, though I don't see a difference here. :-)

> > > I hope I clarified above.  However, I _do_ believe the new species
> > > evolving had a crucial and global role.  For example, the most popular
> > > hypothesis for pterosaur extinction _is_ competition/predation from
> > > birds!
> >
> > What on Earth (or elsewhere!) can compete with *Quetzalcoatlus*???
>
> Falconimorphs eat Q babies.

Evidence for K falconiforms? 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?

> > Since when do species evolve into an occupied niche?
>
> I would think all the time--if they are better competitors.

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.

> Just as a
> mundane example: a bird develops the ability to take off vertically.

*Confuciusornis*. :-)

> It
> therefore avoids capture and can hang out near a pterosaur's nest with
> impunity waiting for the right moment to snatch a hatchling.

*Boluochia*. As old as *C.* -- middle EK.
BTW, this would not be an example of "evolving into an occupied niche".

>  I mean,
> yours seems like a ridiculously categorical statement.  I would rather
> say: since when doesn't evolution provide better competitors to challenge
> current niche-holders.

I do think that evolution doesn't do that. An exception is when the
niche-holders are confined to one continent (or several... anyway not all),
and their niche is empty on another continent. Something can evolve into
this niche there then. When later the continents become connected (why
continents... some sort of strict geographical separation), then competition
can begin. Then I think that this will result in more niche partitioning
than extinction, but some extinction will probably happen. It is a way
around the example above.

> > Predation -- where is the predator? *Ichthyornis* looks like a suitable
> > candidate, but it is far too old. :->
>
> Do you really believe the fossils represent a substantial portion of
> extinct diversity?

In some formations -- yes. See the paper mentioned above.

> 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?

> Pre-bolide climates determined hibernation ability.

Oh, that's what you were talking about. :-)

> Creatures that don't normally hibernate cannot
> be induced to just because of sudden nuclear winter.

Sure.

> Therefore, since most mammals (in w. int. of NA, anyway)
> experienced equable climate, they are unlikely to have been able to resort
> to this strategy.

Yes, and they may not have needed to. It may not be a stretch to imagine
that enough seeds and insects were around to sustain a few viable mammal
populations.

> > [...] but the neornithean groups known from the Maastrichtian so far (to
me, I
> > must add, but apparently there's not much more published so far than the
> > abstracts I've read) don't seem to have depended on "green food chains".
> > When enough food (and thermoregulation) is available, hibernation is
> > unnecessary.
>
> Birds today depend on them...why not birds pre-K/T?...

OK -- in the long run almost all animals depend on them. But for a few
months that isn't the case for granivores, insectivores, detrivores and
suchlike, and those carnivores that eat these ("brown food chains").

> Unless we are back
> to the fanciful cracking of crabs of Feduccia.

Can't remember him writing that... the ability to crack crabs is a rather
formidable specialization, isn't it?

> This fantasy is just a
> method of making happen what obviously happened: birds could not have
> possibly survived in green niches, therefore only birds dependent on
> non-green food chains could have survived.  But, as you know, exactly who
> were the bird survivors of the K/T is still a hot topic.

Neornithean clades known to be present in the Maastrichtian:
-- Anseriformes. Rather omnivorous.
-- Gaviiformes. Eat fish that eat detritivorous invertebrates.
-- Forgot what else, but not much so far.

Neornithean clades inferred by tree topologies to be present in the
Maastrichtian:
-- Palaeognathae. If all basal paleognaths looked like tinamous, then see
Galliformes.
-- Galliformes. Granivorous-omnivorous.
-- Uncertain what else, but for most probably see Anseriformes and
Gaviiformes.

In contrast...
-- Avisauridae. Arboreal. No trees, no avisaurids.
-- Hesperornithiformes. Won't like a Strangelove ocean.

Might fit the picture, don't you think?

> > > Presumably in order to not advertize the presence of his nest,
> > > the male emu goes without food and water for 40 days (from memory) or
so.
> >
> > 40 days?!? Are you sure?
>
> Coombs has it as: "Once a male emu has settled on his clutch, he remains
> on it almost continuously, eating essentially nothing and only rarely
> drinking...during the eight weeks of incubation" (ref. if needed).  Pretty
> incredible, right?

Yes. But "almost", "essentially" and "only rarely" make it sound much more
plausible than before. :-)