RE: Sereno's (2005) new definitions

[Michael Mortimer <mickey_mortimer111@msn.com>]

Tim Williams wrote-

> > Yep -- but it will still be a troodontid (and probably a quite derived
> > one). That should be unambiguous enough for not harming its function as a
> > specifier.
>
> Here's the problem...  If a taxon is deemed to be a nomen dubium it becomes 
> an invalid OTU, and so must be excluded from phylogenetic analyses.  
> Therefore, its exact position in a phylogeny cannot be determined.  I would 
> think this would mean that the taxon in question would be invalidated as a 
> specifier.

Not so.  You can run the Troodon formosus holotype premaxillary tooth in a 
matrix as an OTU.  In fact, it's easy to do such because there are so few 
characters to code.  For instance, in the TWG matrix, it can be coded for-
80. Premaxilla toothed (0) or edentulous (1).
86. Serration denticles large (0) or small (1).
87. Serrations simple, denticles convex (0) or distal and often mesial edges 
of teeth with large, hooked denticles that point toward the tip of the crown 
(1).
88. Teeth constricted between root and crown (0) or root and crown confluent 
(1).
91. In cross section, premaxillary tooth crowns sub-oval to sub-circular (0) 
or asymmetrical (D-shaped in cross section) with flat lingual surface (1).
After running this in PAUP (and deleting their Troodon OTU), the Troodon 
holotype comes out in a clade with Byronosaurus, Sinornithoides and the two 
Saurornithoides species.  Thus, an exact enough phylogenetic position has 
been determined to define Troodontidae with.  It's true that a nomen dubium 
won't ever have an _exact_ position in an analysis containing at least two 
taxa it's indistinguishable from, but very few taxa have exact positions 
from analysis to analysis anyway.

Mickey Mortimer