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Re: Cretaceous taeniodont
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?