Re: The K-T boundary in Nanxiong

["David Marjanovic" <david.marjanovic@gmx.at>]

----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Wednesday, June 12, 2002 5:11 AM

> Nick Longrich said:
> > Re: Elephant bird eggs, it is very common to find elephant bird
> > eggshell on the beaches in Southwest Madagascar, [...]
>
> [...] Any idea why these shells are in the Southwest?  Did the
> birds live only in the SW?

The shells aren't _only_ in the southwest, are they?

> Does any hypothesis predict total, instant, annihilation?

When "instant" means "between a few days and a few 1000 years", then an
impact does predict that this is fully possible.

> Why wouldn't a
> bolide spare a species or two in some remote valley?

Maybe it would, like the P-Tr and Tr-J events spared a species or two of
ammonites. But in the empty world that follows, such species are expected to
radiate -- as the ammonites did -- instead of dying out. Oh, er, and many
species -- especially ones of big body size -- won't survive for long in
something as small as a remote valley.

> Given the gross survival of other clades,

I disagree.
        Some time ago I lamented about how little I knew about how many fish
clades survived it... Hybodontiformes snuffed it. Pycnodontiformes, a group
that fed on hard stuff like maybe corals, molluscs and/or echinoderms, got
caught, too, according to Vertebrate Palaeontology, but Guimarota -- A
Jurassic Ecosystem says they lasted much longer; their round, hard teeth are
certainly very good to rework, but that's all I know. Semionotidae seems to
have died out at the boundary, and many other groups -- Macrosemiidae,
Pachycormidae, Aspidorhynchidae, Leptolepidae, Ichthyodectidae -- could have
done likewise, but Benton isn't explicit.

> it has to be more likely than not that a couple of species
> _did_ survive.

Then we'd have to explain why these species died out then...

> But the chance of finding something like this could be very
> small.

... and why they never diversified.

> It would be much easier to convince an alien biologist of the
> possibility of relict populations than of a total surgical instant
excision
> of a diverse taxon.

Certainly not if they've had a big impact recently! :-)