[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: (extinction)



----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Friday, July 05, 2002 11:39 PM

> Wouldn't you agree that if we found a trove of neornithine
> ancestors of modern orders in pre K/T that this would affect
> conclusions.

It would certainly affect conclusions about the severity of the event in
that place.

> What if we also found a decrease in enantiornithine
> diversity pre K/T?

People would simply shout "Signor-Lipps effect". =8-)

> Simply: I don't buy global segregation of opposite and new
> birds;

There were Neornithes pretty much everywhere, it seems, and there were
Enantiornithes in southern SA, Madagascar and, at least in the EK, in
Australia, so a few Antarctic ones are expected (but haven't turned up so
far). The scenario I suggested ("imagine 100 %...) makes this compatible
with the impact theory.

> and, if both clades enjoyed pre K/T diversity,

Uncertain at least for Neornithes.

> I don't see a
> weakness in enantiornithines such that it would predispose them to higher
> extinction levels;

Numbers alone are very little protection against an impact-induced mass
extinction.

> I am just skeptical of estimates of the power global devastation on one
> hand,

why?

> and the inability of some clades relative to others to withstand
> them.

I'd formulate that differently: the _slightly_ better ability of some clades
relative to others to survive them.

> Clearly, when Lillegraven, Eberle, Currie, examine these horizons
> and can hardly tell when one starts and the other stops...well...

Fluvial deposits. Channels cutting through the boundary layer, not to
mention reworking of fossils... right? Never been there. :-)

> and, in
> other locations, Horner looks and finds changes afoot earlier than dogma
> suggests,

and then, Sheehan comes along, picks up everything that doesn't move, and
finds a catastrophic extinction?

> and when Ir turns up in inappropriate levels...

News to me.

> these may all be
> justified in the end and brought in line with the bolide idea (like
> Darwin's hypothesis for the formation of coral reefs!)...we'll see.

Can't imagine how.

> Is Archibald's claim that placental extinction in NA
> were almost all pseudoextinctions still supportable?

I don't know, but it doesn't look like it is support_ed_ currently. :-)
Can't find John Alroy's gigantic database right now. It includes lots of
statements about direct ancestry.

> Paleontological conclusions should be drawn from the totality of the
> evidence.  I'm just saying that I don't find the terrestrial vertebrate
> evidence convincing.

Well... if the terrestrial vertebrate evidence doesn't fit all other
evidence, then I think it's likely our interpretation of the former, rather
than of all the latter, is incorrect.

> Specifically, however, we have seen marsupial ass kicked
> before...

No known K metatherian is a (crown-group) marsupial. :-)

> and we are witnessing marsupial ass being currently whupped in
> Australia as we speak;

Well... this is not all placentals vs. all marsupials. To take the example
that's least relevant for the K-T, kangaroos are said to be more efficient
herbivores than sheep. I have read of dingos eliminating Tasmanian tigers
and devils from Australia's mainland, but I haven't heard of them
threatening marsupial mice (more similar to pediomyids AFAIK). But most
importantly, what we have there is immigration. There's currently no
evidence for this happening at the K-T.

> and, we currently have no hypotheses for the
> elimination of enantiornithines should it turn out that they were
> selected.

Arboreality, for example.

> Indeed, other hypotheses enjoy better evidenciary
> support: pterosaurs were practically gone by then

Pterosaurs as a whole, but not azhdarchids.

> and we need a non-bolide
> targeting killer for them.

What??? Why do you think they would have survived the impact??? You don't,
do you?

> It should have wings (because flying things
> can take refuge from non-flying things),

... but flying things won't fly everywhere.

> and it should be a new species
> (otherwise it would have happened before).

Really new. Not evolved in place, so that its prey could have coevolved with
it. It must have immigrated from somewhere. And probably it must suddenly
have been able to reach even the most remote islands where albatross-like
azhdarchids might have nested.

> And, so I ask: would it change
> your mind if it were KNOWN
> that neornithines played the leading role in
> these extinctions?

How could that be known? :-)