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Re: Avian Ancestors, new book on theropods



Thomas R. Holtz, Jr. <tholtz@umd.edu> wrote:

>> I'm not sure the new name Averaptora is essential.  Zhang et al.
>> (2008) previously defined Avialae as the most inclusive clade
>> including crown birds but not dromaeosaurids (specified by
>> _Deinonychus_).  So their Avialae is equivalent in content to Agnolin
>> and Novas' new clade Averaptora.
>
> Ummm... GAUTHIER (1986, p. 36) defined it in this manner (Aves and all
> taxa closer to Aves than to Deinonychosauria).


My reading of Gauthier (1986, p.36) is a bit less clear-cut than that.
 In fact, I would say that his original Avialae was a bit of a mess.


According to Gauthier “the name Avialae is applied to Ornithurae plus
all extinct maniraptorans that are closer to Ornithurae than they are
to Deinonychosauria” - clearly a stem-based definition.  However,
Gauthier intended the new clade Avialae to be a replacement for the
traditional Aves, which included _Archaeopteryx_.  So although
Gauthier didn't use _Archaeopteryx_ as an internal specifier as part
of a node-based definition, the implication is that he intended his
Avialae to include _Archaeopteryx_.  At least, that's my take on it.


Thus, subsequent studies have disagreed over whether Avialae is
stem-based (including crown birds, excluding dromaeosaurids) or
node-based (including _Archaeopteryx_ + crown birds).


Either way, Agnolin and Novas seem to have used Avialae for the
_Archaeopteryx_ + crown bird clade.  This is against the explicit
stem-based definition of Gauthier for Avialae, but agrees with
Gauthier in the inclusion of _Archaeopteryx_ - but nothing more basal
than _Archaeopteryx_.  So if Agnolin and Novas had applied Gauthier's
1986 definition of Avialae, it would make their Averaptora redundant.



P.S.  I only mentioned the definition of Avialae given by Zhang et al.
(2008) because their stem-based definition has species-level
specifiers, in accordance with PhyloCode: the most inclusive clade
including _Vultur gryphus_ but not_Deinonychus antirrhopus_.  Although
I could equally have used Maryanska (2000): _Passer domesticus_ but
not _Dromaeosaurus albertensis_ or _Troodon formosus_.



Cheers

Tim