Re: Diatryma and mammals!

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

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,
though. 

> >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 
paludal.
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.