Re: Doesn't George have a point?

["T. Mike Keesey" <tmk@dinosauricon.com>]

On Thu, 29 Jun 2000, Jerry D. Harris wrote:

> (1) Who said dromaeosaurids were avian _ancestors_?  Last I understood, they 
> were considered the _sister_group_, but not actual ancestors.

This is the prevailing hypothesis, but I have seen another one where
Dromaeosauridae as usually understood is paraphyletic:

--+--Oviraptorosauria
  `--+--_Dromaeosaurus_
     `--+--Avialae
        `--+--_Deinonychus_
           `--_Velociraptor_

> Thus, the common ancestor of both birds and dromaeosaurids must have
> been present prior to _Archaeopteryx_; _not_ necessarily that
> dromaeosaurids go back that far (although this brings up when one
> would call something stemming off from that ancestor a
> "dromaeosaurid"...)

Dromaeosauridae has been defined as a node-based clade: 
{_Dromaeosaurus_ + _Velociraptor_} (although this definition would be
problematic if the above phylogeny were true ... all birds would be
dromaeosaurids!)

Deinonychosauria is a stem-based clade: {_Deinonychus_ <-- Neornithes}
 
> (2) Read more literature.  Chris Brochu and Mark Norell penned a great 
> article on this very issue, which _was_ discussed on this list, and showed 
> that there really _isn't_ a gap:

Well, there are gaps, but they're much less under the maniraptoran theory
of bird origins than under alternate hypotheses.
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T. Michael Keesey <tmk@dinosauricon.com> | AIM <Ric Blayze> | ICQ <77314901>
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