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Re: Everyone's discussing bird origins...



At 10:22 AM 9/30/96 -0500, you wrote:

>I'm not wedded to BCF, either. But I have yet to see something better, and
>until I do, I'll carry the belief that the BCF phylogeny of dinosaurs and
>birds is the correct one.

Here is an option:

When one considers the range of a species, one discovers that within
the range, there exist a series of populations, each one more-or-less
isolated from one another.  During good conditions, these populations
expand their boundaries, allowing animals from different populations
to interbreed, maintaining genetic homogenaity.  When conditions are
poor, the populations restrict their boundaries, preventing
interbreeding.  If a particular population stays isolated long enough
to become genetically/behaviorally different from the rest of the
populations, then that isolated population is actually a new species
(the definition of speciation).

Going with this definition, what if there was a basal aboreal theropod
(I'll play cladist for the moment) with a number of populations that
were restricted over time.  In one of the populations, the trend for
powered flight starts, leading to Archy.  At the same time, another
population starts a trend which leads to Dienonychus.  Call this
definition: Birds Are Dienonychus Cousins (BADC).

This senario overcomes one of my principal objections to BCF: what
evolutionary trend would force a fully developed bird to adapt to a
cursorial existance when the ground is full of small predators (read:
competition).

Rob Meyerson
Orphan Vertebrate Paleontologist

***
"No, your monkey is correct."
        -Slartibartfast; _The Hitchhikers Guide to the Galaxy_