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Re: (extinction)



----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Thursday, July 04, 2002 3:34 PM

> On Wed, 3 Jul 2002, Michael Habib wrote:
>
> > I still do not see how competition from placentals, predation from
> > neornithines, and the like are viable explanations (in a direct sense,
> > at least).
>
> What I meant was: to make the case for mass extinction caused by a diffuse
> agent, i.e., dust, sulfates, whatever, one must rule out alternative
> hypotheses.

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.

> At issue are two extinctions, local marsupials and
> enantiornithines.  Both of these clades are a big problem for the bolide
> inasmuch as neither presents a reason why they were targeted and not their
> ecological equivalents, placentals and neornithines respectively.

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.
        How much of the crown group Placentalia survived is unknown because
no member of this group is currently recognized from the K. If you mean
Eutheria, these were "targeted", as I repeated yesterday.
        How much of Neornithes survived is almost as unknown. Anyway,
Neornithes is just a part of Euornithes... Hesperornithiformes: gone.
Ichthyornithiformes: gone.

> We understand a possible mechanism
> for dinos--lack of bulk food for bulk animals--

That alone would not have been enough, and it doesn't need to. Big animals
might die from falling. Imagine a sauropod in "a magnitude 11 earthquake"
(Rampino). Then the wildfires. The acid rain, with nowhere to hide -- "size
does matter" here. And so on.

> but we don't have one for our diminuitive niche holders.

Burn down all forests (and grasslands) worldwide. Then count the percentage
of extinct rodent species. Won't approach 100 %, but you'll still see a mass
extinction.

> And so,
> the bolide is forced to propose mechanisms which I find
> very far-fetched: e.g., a hermetical seal seperating enantiornithines in
> the North and neornithines in the south.

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? :-)

> > Reason: these seem very unlikely to act as global events, nor are they
> > patterns to which the dinosaurian (and other) taxa had not been
> > exposed.  LOCAL extinctions from competition are common.  A GLOBAL
> > mass extinction requires a NOVEL effect across the entire range of
> > several groups severe enough to reduce ALL viable populations.
>
> 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*???
Since when do species evolve into an occupied niche?
Predation -- where is the predator? *Ichthyornis* looks like a suitable
candidate, but it is far too old. :->

> This is a novel effect, right?  And it is also global.
>
> > [...] perhaps hibernation would be important, etc.
>
> [...] 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.

> 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.

> 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?

> As Leigh Van Valen has said: causes of extinction
> are often a matter of taste.

When did he say that? In the 60s maybe, when it was true? :-)

> Ultimately, it is our dichotomous brain that
> forces us to choose alternaives that don't exist in reality
> (I said that, not Leigh).

Ultimately, it's our desire for harmony that prevents us so often from
knowing a contradiction when we see it. I wrote that right now. :-)