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RE: Caudipteryx not a bird and more from APP

> From: Dora Smith [mailto:villandra@austin.rr.com]
> Sent: Thursday, February 03, 2005 8:02 PM
> To: tholtz@geol.umd.edu; Mickey_Mortimer111@msn.com; dinosaur@usc.edu
> Subject: Re: Caudipteryx not a bird and more from APP
> You've convinced me that caudipteryx was not ancestral to birds; but I'm
> having trouble with the idea that this proves that archeopteryx was
> ancestral to birds.
By no means mix up the two hypotheses: they are not connected!

One can easily accept that a) Caudipteryx is an oviraptorosaur while still 
accepting that b) Archaeopteryx is not directly on the
line to modern birds.  These are perfectly compatible hypotheses. The important 
thing would be what the best evidence shows.

And in most studies Archaeopteryx is closer to birds than either is to 
Caudipteryx, but that doesn't mean that Archaeopteryx is
ANCESTRAL to modern birds. After all, Utahraptor is also closer to birds than 
is Caudipteryx in most recent studies, but nobody
suggests (for a wide variety of reasons) that Utahraptor is directly ancestral 
to modern birds.

One of the most important aspects of the cladistics revolution is the 
recognition that the chance that we have actual sampled the
real, true, honest-to-goodness ancestral population from which another group we 
are interested is vanishingly small. The geologic
record is very spotty, and all other things being equal we wouldn't be able to 
tell directly if a particular fossil represents a)
the population directly ancestral to the other group in question or b) a close 
relative to the population directly ancestral to the
other group.

So instead of doing the old-fashioned ancestor hunt, we instead search for 
*patterns of recency of common ancestry*. These patterns
are inferred by the basic evolutionary premise of descent with modification.

I hope this helps,

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796