Re: Extinction once again (was Re: ARE ORNITHOPODS BORING?)

[John Bois <jbois@umd5.umd.edu>]

On Sat, 17 Feb 2001, David Marjanovic wrote:

> Wrongo!
> 1. This regression took _4 million years_, spanning quite some time before
> and after the K/T.

...adding stress to species which nested on the shores of the "Oceans of
Kansas."  Habitat loss is the main cause of  today's extinctions--why
would we doubt that it was important in other times--especially when we
know that vast tracts of potential nesting territory were reduced to zero?

> 2. Due to some odd effects of earth axis precession or so (I can
dig up the
> ref later), sea level dropped in the western half of the northern and the
> eastern half of the southern hemisphere whereas it rose in the rest of the
> world. Yet the extinction was global.

Lest we take news reports too literally, we should remind ourselves that
extinction is only recorded in one location!

> 3. You are not trying to suggest that ALL Maastrichtian non-_neornithean_
> dinosaurs nested in "wetlands"!?!

Certainly not.

> 4. Lots of terrestrial egg-laying vertebrates survived (turtles, crocs,
> lizards/snakes, tuataras, monotremes...)...

They are mostly very small and can hide their nests in a greater variety
of places.  Crocs are totally dependent on wetlands, though.

> 5. Marsupials, for example, were severely hit. How come?

Their extinctions are timed to placental radiation at the K/T.  So
replacement is a thoroughly respectable hypothesis for this.  Why wouldn't
diverse creatures have diverse reasons for their disappearance--unless
we're trying to shoe-horn observable phenomena into non-observable
scenarios.

> 6. Plankton (and all animals with planktonic larvae) was severely hit, which
> is not easy to explain with a regression.

Not yet timed to terrestrial extinctions.