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Re: Caudipteryx not a bird and more from APP



I do often see information that is a few years old.

I don't specifically remember that anyone thought caudipteryx was in the
lineage to modern birds+ADs- only that some of them appeared to be more likely
to be int he lineage to modern birds than archeopteryx.

You appear to present two good logical reasons for thinking birds aren't
descended from archeopteryx - do I correctly understand that you yourself
don't accept them, and that you think that birds are descended from
archeopteryx?

I know that birds are thought to be monophylatic.  Now, in the time when
they evolved that would have included a pretty big group of animals.   They
were already so diverse in the Cretaceous, that I don't think that it's
proven they all evolved from a single common ancestor among the dinosaurs
that we know of.

I can see how the skeletons of birds differ from thsoe of their cousins -
but multiple lines of therapods were evolving in similar ways because those
ways constituted strong adaptive advantages.   I am not saying that birds
did NOT evolve from a single line, but I'm not convinced it's proven.

Yours,
Dora Smith
Austin, Texas
villandra+AEA-austin.rr.com
----- Original Message -----
From: +ACI-Tim Williams+ACI- +ADw-twilliams+AF8-alpha+AEA-hotmail.com+AD4-
To: +ADw-dinosaur+AEA-usc.edu+AD4-
Sent: Thursday, February 03, 2005 3:44 PM
Subject: Re: Caudipteryx not a bird and more from APP


+AD4-
+AD4- Dora Smith wrote:
+AD4-
+AD4- +AD4-My understanding is that caudpteryx and some other close relatives of
birds
+AD4- +AD4-are controversial as to whether they are birds.
+AD4-
+AD4- I think that particularly controversy has dissipated over the past few
+AD4- years.  There is strong (probably compelling) evidence that 
+AF8-Caudipteryx+AF8-
is
+AD4- not a bird, but an oviraptorosaur.  Oviraptorosaurs are not currently
+AD4- considered birds (i.e., a member of the clade Avialae) - but this may
+AD4- change.  Thus, currently, +AF8-Caudipteryx+AF8- is not usually considered 
a bird,
+AD4- and its placement at the base of the Oviraptorosauria has strong support.
+AD4-
+AD4- +AD4-It is also sometimes
+AD4- +AD4-argued that they are evidence that archeopteryx are not birds' direct
+AD4- +AD4-ancestor but a dead end.
+AD4-
+AD4- I'm not certain how +AF8-Caudipteryx+AF8- could be brought into this 
argument, pro
+AD4- or con.  The belief that +AF8-Archaeopteryx+AF8- is not the DIRECT 
ancestor of
+AD4- modern birds comes from anatomical evidence (+AF8-Archaeopteryx+AF8- has 
one or
more
+AD4- derived characters that preclude it from being the avian ancestor) and
+AD4- chronological evidence (+AF8-Archaeopteryx+AF8- lived too late in time to 
have
given
+AD4- rise to the diversity of bird taxa we see in the Early Cretaceous).
+AD4- Personally, I don't regard either argument as especially compelling.
+AD4-
+AD4- +AD4-It would be really good to be able to do genetic studies to 
determine if
+AD4- +AD4-all
+AD4- +AD4-modern birds are really descended from teh same lineage of dinosaurs 
- I
+AD4- +AD4-see
+AD4- +AD4-real cause to wonder.
+AD4-
+AD4- Most ornithologists and paleontologists would disagree.  The morphological
+AD4- and molecular both overwhelmingly support the hypothesis that modern birds
+AD4- (Neornithes) are monophyletic.
+AD4-
+AD4- +AD4-More than one line of dinosaurs were evolving in birdlike directions.
+AD4-
+AD4- I think it's more accurate to say that certain theropod lineages evolved
+AD4- bird-like traits independently (compare mononykines to ornithothoracine
+AD4- birds, for example), and one of these lineages became birds.
+AD4-
+AD4- The notion of a polyphyletic Avialae has some supporters, as does the
+AD4- associated hypothesis that powered flight evolved TWICE in dinosaur
+AD4- evolution (I've heard Kurzanov's name associated with this).  However,
99.9+ACU-
+AD4- of researchers regard the birds (Avialae) as monophyletic, and hold that
+AD4- flight evolved just once in dinosaurs.
+AD4-
+AD4-
+AD4- Tim
+AD4-
+AD4-