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