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Re: (extinction)




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.

> What about: Almost all mammals were killed. A few metatherians north
> (Peradectidae) and south (Neometatheria), a few eutherians(Cimolesta,
> Leptictida, Placentalia if it doesn't include the former two), a few multis
> (I know too little about their systematics), one known dryolestoid
> (*Peligrotherium tropicalis*), an unknown but certainly small number of
> monotremes and gondwanatheres survived. That's not much. 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).  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.  I think Lillegraven and Eberle said what is a good "at
least" statement: "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)."  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.  In ecological terms--since
competitiveness is completely dependent upon specific
habitats/niches--this is a _non sequitur_. (But I'm not sure that _is_
what you're arguing and I apologize for my lack of expertise in evaluating
your species' lists if it is not!--and thanks for taking the trouble, b y
the way).
Also, see http://www.concentric.net/~Ewdewar/research/SVP97/ for
interesting discussion of dietary diversity at Puercan 1.

> 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.  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.  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.

> > 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.

> Since when do species evolve into an occupied niche?

I would think all the time--if they are better competitors.  Just as a
mundane example: a bird develops the ability to take off vertically.  It
therefore avoids capture and can hang out near a pterosaur's nest with
impunity waiting for the right moment to snatch a hatchling.  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.

> 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?  I'm not suggesting anything fantastic here--just an
effective predator on pterosaur chicks at all locations.

> > [...] I'm not so sure--and, in any case,
> > extinctions in "equable" climates--equatorial, at least--are unlikely to
> > involve hibernation
> 
> What equatorial climates? What we're talking about is an impact winter. A
> big impact is expected to impact the climate very hard, and there's evidence
> that this one did.

Pre-bolide climates determined hibernation ability.  Creatures that don't
normally hibernate cannot be induced to just because of sudden nuclear
winter.  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.

> > Also, birds are not great
> > hibernators--
> 
> -- 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?...Unless we are back
to the fanciful cracking of crabs of Feduccia.  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.

> > 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?