Re: Sereno's (2005) new definitions

["Jaime A. Headden" <qilongia@yahoo.com>]

David Marjanovic (david.marjanovic@gmx.at) wrote:

<Yes, and these comparisons are able to tell that it belongs into the same
clade as the other taxa usually regarded as troodontids. They even tell us that
it belongs into a certain subclade (but not where within that subclade).>

  Actually, I've been kind of arguing that this kind of certainty is NOT in
evidence. We can argue that it IS related, but this data is based on a single
tooth. We have no idea what an entire dental series or the implantation of them
is like for *T. formosus* due to it's isolated nature, and this lack of
certainty, as I stated before, reduces its comparability so much that being
able to argue what other taxa are troodontids is making a hefty assumption:
that the tooth is the same as the kinds of teeth we find in *Saurornithoides*
and the like. The lack of any frame of reference makes it impossible to
determine that the *T. formosus* type derives from the same kind of animal as
*Saurornithoides*, that they in fact share a more recent common ancestor
exclusive of Aves within the Maniraptora, or in fact anywhere. The teeth of
other "troodontids" (in this sense) renders this issue problematic, to say the
least.

  As Tim noted, this can all be solved by appointing a neotype, which I would
advocate on the basis of consistency and context. There is even a decent
specimen available that directly allows comparison to other North American
troodontid specimens that is available for this purpose.

<Therefore we know enough about its phylogenetic position that we can, IMHO,
safely use it as an internal specifier for a (not _too_ small) clade.>

  The fact that it's nature is co indistinct, makes it problematic, as
repeating before, to use the tooth as an internal specifier, especially when
the uses of that taxon would hold that it would include all these other
specimens that may or may not be related, whatever the cladistic analysis says.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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