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Re: Greg Paul is right (again); or "Archie's not a birdy"



On Wed, Jul 27, 2011 at 2:28 PM, El PaleoFreak <saichania@gmail.com> wrote:
> El 27/07/2011 19:34, Mike Keesey escribió:
>>
>> Very cool!
>>
>> Yet another reason why the definition of "Aves" should not rest on
>> _Archaeopteryx_.
>
> I'd really like to read about those reasons. Could you or anyone explain or
> provide a link about this issue? Thanks!

There are several issues at play here. Scott did a good job summing up
the arguments for using a crown clade definition. For a more thorough
discussion, I highly recommend Gauthier & de Queiroz (2001), available
here: 
http://vertebrates.si.edu/herps/herps_pdfs/deQueiroz_pdfs/2001gaudeqost.pdf

But I was referring more to the fact that using basal taxa as
specifiers in definitions is inherently unstable, because basal taxa
lack derived traits that can clarify their positions. Morphologically,
Archaeopteryx is so close to the eumaniraptoran ancestor that is is
almost impossible to tell whether it is closer to dromaeosaurids,
[modern] avians, or neither. Even this study only found very low
support for placing it in Deinonychosauria.

Sereno presented an argument for using deeply nested specifiers, as
opposed to basal specifiers, here:
http://sysbio.oxfordjournals.org/content/54/4/595.full#sec-15
(Although he didn't always practice what he preached:
http://taxonsearch.org/dev/taxon_edit.php?Action=View&tax_id=43 )

-- 
T. Michael Keesey
http://tmkeesey.net/