Re: Caudipteryx not a bird and more from APP

[Tim Williams <twilliams_alpha@hotmail.com>]

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 
> all
> modern birds are really descended from teh same lineage of dinosaurs - I 
> see
> 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.


Tim