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Re: Diatryma and mammals!
On Sun, 2 Aug 1998, Ronald Orenstein wrote:
> >An important afterthought: eurytropy is common in animals dependent upon
> >wetlands. But they need the deep cover of the marsh, pothole, swamp,
> >whatever, to reproduce. When this cover disappears, so do they. Indeed,
> >predation is a major source of nest destruction in waterbirds of the
> >prairies (ref. if needed) which are dependent upon potholes for nesting.
> True, though we have no idea if this applied to Diatryma.
Maybe "no idea" is a little strong. We do have at least a _hint_ that it
applied to diatryma inasmuch as they disappeared when the wetlands
disappeared. I do realize there are plenty of alternate hypotheses,
> >Also, if something did not prevent radiation of diatryma into more diverse
> >niches, a thoroughly reasonable expectation is that we would observe
> >adaptive radiation in that body plan!
> This could be an artifact of the fossil record, of course. And some mammal
> lines (eg Tubilidantata) aren't wildly diverse either.
But what Martin is saying is that the diatrymid fossil record _is_
evidence of an adaptive radiation; that the reason they radiated is
because there were no non-avian dinosaurs; and that mammals posed no
threat to them. If nothing else, this hypothesis is threatened by Andors'
reasonable interpretation of the facts--i.e., that diatryma may have been
Also, I am arguing that we should, if Martin were correct, see more
adaptive radiation. Tubilidantata are (were?) a fairly specialized clan
within a community of diverse mammals with a similar-sized body plan:
competition was likely intense for niche requirements. Diatryma, says
Martin, had _no_ competition, neither from birds nor mammals! If they
walked into such a garden of Eden we would expect more morphological
diversity arising from this no-cost radiation.