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Re: Dinosaur diversity (was Re: paleontologist, dinosaurs...)



In a message dated 96-11-21 03:15:28 EST, longrich@phoenix.Princeton.EDU
(Nick Longrich) writes:

>         There's no reason to assume that they took so long to evolve.
> Archaeopteryx-like birds might have evolved from tree-climbing (or, if you
> prefer, running) theropods in something like fifteen million years, give
> or take a few million.
>         That sounds rapid, but remember that bats and whales appeared very
> well formed in the Eocene. It is possible that a pre-KT radiation of the
> cetacea and chiroptera was underway already, but it seems to me somewhat
> more plausible that that after the great vaccum left by the extinction of
> sea reptiles, most birds and pterosaurs, that swimming and flying forms
> should evolve. I'm not saying it did happen this way, but it seems like a
> possibility. 

What you're talking about is the evolution of flight, not the evolution of
birds. This may indeed have occurred fairly rapidly--perhaps, as you suggest,
in about 15 million years of pre-_Archaeopteryx_ evolution. But there is
simply nothing particularly birdlike in the fossil record between _Protoavis_
(whatever that turns out to be) and _Archaeopteryx_, a period spanning about
50 million years. So we don't know just where in this 50-million-year span to
place those critical 15 million or so years when flight evolved.

I prefer "tree-climbing"...