Re: Avian Monophyly (Was Re: Sheesh)... :-)

[Tim Williams <twilliams_alpha@hotmail.com>]

Jamie Stearns wrote:

> As for Rahonavis, the idea that it was more closesly related to 
> Buitreraptor and Unenlagia than to birds appears to make sense in light of 
> its "primitive" structure in a time when things like >Ichthyornis and 
> Vegavis already existed. Convergent evolution might have led to a body plan 
> resembling Archie, while being a member of a different dromaeosaur lineage.

Convergent evolution is one explanation.  Another explanation is that 
critters like _Buitreraptor_, _Unenlagia_, _Rahonavis_ and _Archaeopteryx_ 
share a similar body plan because this body plan is ancestral for the 
Aves+Deinonychosauria clade (Paraves).

The idea that _Rahonavis_ is a flying dromaeosaur is certainly alluring, but 
I have a feeling that future analyses will put _Rahonavis_ back in the Aves, 
closer to _Archaeopteryx_ and other traditional birds.

BTW, something else that came up on this thread... If theropods like 
_Caudipteryx_ and dromaeosaurs are demonstrated to be secondarily flightless 
(i.e., descended from flying theropods) this does not necessarily mean that 
they belong in Aves.  Aves is not defined by flight ability (not usually, 
anyway).  It may be that flight is primitive for a much more inclusive group 
(say Paraves, or even Maniraptora).  Thus, we could have secondarily 
flightless non-avian theropods.

> Of course, the fact that it's geographically close to the unenlagiines is 
> another good argument for it being of that group.

Hmmm... not sure about that.

Cheers

Tim

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