Re: Hell Creek (long)

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

----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Monday, June 03, 2002 3:59 AM

> > One thing is certain -- zalambdalestids are pretty distinct from every
known
> > Cenozoic mammal. They'd be pretty easily recognizable. For example, they
> > retained epipubes, something no known Cenozoic eutherian has.
>
> ...and epipubes or something similar predisposed them to be susceptible
> to the bolide?

No, why? Did I say that? "We almost never know why things become extinct".
:-) Sorry for that non-argument, but it's expected that in an impact-induced
mass extinction most of most groups die out, so why shouldn't that hold for
Eutheria. It may well have been a coincidence, just like the fact that no
toothed bird survived may be one. All I said is that we'd pretty certainly
know about Paleocene zalambdalestids if there were any.

> > Really, what could do it? Competition? Certainly not. Nest
> > predation? Mosasaurs and plesiosaurs were viviparous.
>
> One might fairly ask the corollary: why were these body plans targeted by
> a bolide when the shark's body plan was not?

May more have to do with a shark's food requirements than with its body
plan. And as someone wrote yesterday, the biggest sharks did die out.

> Do we know how big the neonate was in relation to the adult?

There's someone onlist who knows...

> Did they go on land to deliver (like seals)?

Probably not.

> Perhaps a species of shark preyed them to extinction

Serious, please. That species would itself die out _first_.

> > ammonites _everywhere in the seas_ if not every last one had died at the
> > K-T. Wouldn't we?
>
> What is the status of synchroniety of land vs. sea extinctions?  Last I
> heard this work had not been done.

Must have been several years ago. Pollen & spores allow correlation
sometimes, ignoring the boundary layer itself! We can say for sure now that
the K-T and the P-Tr mass extinctions were simultaneous everywhere,
respectively.

> I'm sure you recognize that without a big
> event there could be all sorts of reasons they went out.

Such as? Remember, we need something that's capable of killing _every last_
ammonite. The P-Tr and the Tr-J just failed (so coincidence is certainly a
factor once populations are hardly viable).