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Diatryma and mammals!



Larry Martin says Diatryma were part of a radiation made possible by the
extinction of non-avian dinosaurs and the still-small size of mammals in
the early Tertiary.  

A.V. Andors, on the other hand, notes their affinities with
anseriformes including a penchant for swamp life.  When the vast swamps of
this time drained off, the Diatryma and their kin became extinct.

I claim these observations are in conflict with each other.  Indeed,
Andors' evidence suggests the Diatryma were perhaps restricted by
something outside swamps--mammals.  One would think that in the something
like 20 million years these birds existed that they could undergo a more
widespread radiation than swamps.  If they had no predators (as Martin
suggests) why could they not extend their range, why could they not
develop traits for use in a wider range of biomes?  Certainly in such a
garden-of Eden such adaptive radiations would be likely--at least
precedent tells us so!

No.  The explanation which makes most sense is that swamps were Diatryma's
realized niche and that other parts of its fundamental were
out-of-bounds--probably, given the size and potential ferocity of Diatryma
adults, due to nest and juvenile predation.

For this to be true one would expect mammals to have a limited ability in
swamps today as well.  And I claim this is indeed the case.  Wetlands are
a traditional haven for waterfowl of today.  With habitat loss comes an
increase in edges.  Mammals in swamps are essentially edge predators,
sleeping dry and moving into the swamp to forage--at least this is what I
have read.  And the only time enough edge-free swamp existed
coincided with the existence of these huge birds.
I would be interested in comments on this idea.
John Bois.