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Re: Struthio/Equus as examples of radiation.



In a message dated 12/26/98 7:43:34 PM Eastern Standard Time,
jbois@umd5.umd.edu writes:

<< Storrs Olson in 198-? said that when the fossil record of ostriches was
 revealed it would be as demonstrative of evolutionary processes as the
 well known Equus story. We are familar with those wonderful horse
 graphics.   >>

The equus story has proven not to be as simple as once thought.  There's a
lengthy discussion at:
<A HREF="http://www.talkorigins.org/faqs/horses.html";>Talk.origins discussion
</A>
It's by Kathleen Hunt.  To quote the summary:

As new fossils were discovered, though, it became clear that the old model of
horse evolution was a serious oversimplification...[I]t was misleading to
portray horse evolution in that smooth straight line, for two reasons: 

First, horse evolution didn't proceed in a straight line. We now know of many
other branches of horse evolution. Our familiar Equus is merely one twig on a
once-flourishing bush of equine species. We only have the illusion of
straight-line evolution because Equus is the only twig that survived. (See
Gould's essay "Life's Little Joke" in Bully for Brontosaurus for more on this
topic.) 
Second, horse evolution was not smooth and gradual. Different traits evolved
at different rates, didn't always evolve together, and occasionally reversed
"direction". Also, horse species did not always come into being by gradual
transformation ("anagenesis") of their ancestors; instead, sometimes new
species "split off" from ancestors ("cladogenesis") and then co-existed with
those ancestors for some time. Some species arose gradually, others suddenly. 

By the way, I wonder how a species arises gradually, if a group of animals is
or is not a species.  (Can an animal be a little bit new species?)  Also,
there's a good quote in the 'Bully for Brontosaurus' essay (which I can't
locate right now) in which Huxley is told that his intermediate forms are too
far separated in space and time to provide a good, continuous narrative of
horse origins.  I appreciate the application of those factors.

At any rate the ostrich may not have as much competition as thought.