Re: Re-emergence of lost features

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

On Fri, 13 Mar 1998, Phillip Bigelow wrote:

> > And why did the phorusrhacoids lose out to the early
> > carnivorous mammals when a similar design survived for so long before?

> Phorusrhacoids may not have lost out to early carnivorans.
> A more likely scenario is that these birds were specialized to
> prey only on one or two prey species which happened to be
> going extinct.

Many hypotheses can be mounted for this extinction.  But birds are
incredibly evolutionarily maleable.  In light of the low diversity of
large bodied birds (roughly one type per southern hemisphere continent),
something more general must be going on.  Whatever this something is, it
is apparently relaxed on mammal-free islands, eg., elephant birds and moa.