Re: Cretaceous taeniodont

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

On Wed, 7 Apr 2004, David Marjanovic wrote:

> The question is wrong. First we need to have a _good_ fossil record that can
> tell us when big mammals _were absent_. Because _this_ is what we currently
> don't know, and what you assume _a priori_ in order to pose your question.

Is there a fossil bias against finding large mammals?  I'm assuming not.
Is there a reason why Cretaceous large mammals are not found but other
periods are?  I'm assuming not.  We haven't found any Martians in the
fossil record either.

> Triconodonts and deltatheridians had been carnivores all the time. Grain?
> Only the multituberculates.

OK.  Let's be more specific.  There was apparently significant size and
niche development in placentals in NA at this time.  The
predator-relaxation hypothesis is at least supported by parallel size
increases in multis and marsupials, though the latter two groups have
isolated large species earlier.

> > Look, all these speciation
> > events are conditional.  Just because we are too far away in time and
> > knowledge to know what the conditions are, doesn't mean species'
> > distribution is random!
>
> Nor is the distribution of fossils random. Nor is the distribution of
> fossils equal! But your questions require a more or less equal distribution
> of fossils through the strata.

'Tis true, I am stuck in the simple "mammals small, dinosaurs big"
paradigm.  Are dinosaurs big?