Re: Tucson Tales III.

[Stan Friesen <swf@tdat.ElSegundoCA.NCR.COM>]

Paul Janke writes:
 >
 > --- Arboreal(trees-down) vs Cursorial(ground-up) Origin of Flight
 ---
 >
 > Martin believes that the proto-bird ancestor was a small
 tree-dwelling
 >reptile. ... eventually lead to fully powered flight.
 >
 > The "trees-down" scenario for flight origin has been hotly
 > contested by the cladists, who favor a cursorial or "ground-up"
 > theory of flight origins.
 > Padian's scenario involves a small warm-blooded therapod already
 > covered in feathers for insulation.

So do I.  I would hope so does Dr. Martin.  Body feathers obviously
evolved as insulation, it is only flight feathers that require
some other explanation.   Feathers originating as insulation is
compatible with both the arboreal and the ground-up model.

 > Longer feathers evolve to assist
 > in the capture
 > of insects that this hypothetical creature pursued while running.

And most paleontologists, even most cladists, find this unlikely.

Actually, the main reason that the cursorial theory was even
considered is that Archeopteryx appeared to be a terrestrial
runner, not a tree dweller.

A recent analysis of the foot structure of A. has cast doubt on this
interpretation, sugggesting that A. was a percher - an arboreal
biped.  This changes the balance, and suggests that the arboreal
model is pefectly consistant with A. as an early bird, *and* with
the dinosaurian origin of birds.

One cladist, the author of Mesozoic Meanderings, has proposed that
there may have been a number of feathered arboreal theropod dinosaurs
from amoung which birds evolved.  This is at least plausible, since
the fossil record of small theropods is terribly fragmentary, and
that of birds even more so.
 >
 > Larry Martin doesn't like the cursorial theory.

I agree, it is a terrible idea that was made necessary by the
apearance that Archaeopteryx was not arboreal.
 > Alan Feduccia has recently
 > published a study in which he concludes that the foot claws of
 > Archie most resemble those of a perching bird.
 >
 > - So why would do many cladists refuse to accept the notion of
 > an arboreal origin of flight? -

I don't know, since those results you mentioned are all very recent
are you sure the non-arobreal theory still has many adherents?
 >
 > Here's a quote from Padian: "Climbing trees does not seem to be
 something
 > they (i.e. therapods) did very well...When you look at the anatomy
 of Archie
 > and the creatures to which it is closely related, you find that
 there isn't
 > a single arboreal character in the skeletons...

When was this published relative to Feduccia's article?
 >
 > [comment - Padian may have been so seduced by his cladistic models
 > that he ignores important evidence and misses this one by about
 > 100 million years.

Or perhaps he is so commited to his personal theory that he
cannot see the contrary evidence?  Given Feduccia's evidence
proper application of the cladistic method no longer necessarily
implies a non-arboreal origin.  To claim that Padian's position
is due to cladism is probably inaccurate.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.