RE: Sereno's (2005) new definitions

[Michael Mortimer <mickey_mortimer111@msn.com>]

Jaime Headden wrote-

> To compare the tooth to another taxon, you MUST
> have a tooth in the same position to correctly evaluate it. Spatial
> relationships among tooth rows are NOT quantified for many taxa, especially 
> of
> value those using tooth-based types, and recent studies where taxa ARe
> quantifies show that while variation is uniform to a taxon, there is still
> substantial variation and a confidence of around 5-10 positions is about as
> close to a single placement in mostly isodont taxa as you can get. In
> heterodont taxa like troodontids, tyrannosaurs, this confidence narrows to 
> 3-4,
> or maybe even 2-3, but these taxa, as in ceratosaurs and dromaeosaurids, 
> can
> have identical uppers and lowers. The diagnostic nature of the *Troodon
> formosus* type depends on its distinctiveness in a phenetic sense, which 
> has a
> high value, but its relevance requires comparability, which is low, despite
> being distinct, because of its isolated nature.

I agree with your general sentiment, and ideally character lists would be 
phrased in such a way to reflect the heterodonty we are increasingly aware 
of.  But in the case of Troodon, its generic or specific diagnosability 
isn't my concern here.  Rather, it's the fact that only derived troodontids 
have teeth like that ANYWHERE in their jaws, so it doesn't matter how 
heterodont troodontids are, or where exactly the Troodon holotype goes in 
the jaws.

>   Furthermore, finding the tooth as a troodontid is largely irrelevant, 
> since
> no one has doubted this placement, and in fact Troodontidae will always 
> contain
> *Troodon* as a matter of correspondence and definition.

It's not irrelevent, it's the entire point of the exercise.  Tim suggested 
Troodon, as a potential nomen dubium, couldn't be used in a phylogenetic 
analysis, and thus couldn't be placed in a cladogram to be used as a 
specifier for a clade.  But if Troodon CAN indeed be analyzed and placed 
inside or outside a certain clade, we can still use it as a specifier 
without problems.

> <But a nomen dubium is just a specimen, an organism.  So if we can run more
> diagnosable specimens through phylogenetic analyses, why not less 
> diagnosable
> specimens?  AMNH 460 has no taxonomic standing, yet Upchurch et al. (2004) 
> ran
> it as an OTU.>
>
>   As Tim said, a specimen can be run as a operational "phylogenetic" unit, 
> but
> its use in taxonomy is very questionable. Thus a taxon based on one such
> specimen as a specifier is also questionable.

I think we're delving too much into semantics here.  OTU's need not be 
taxonomic, regardless of the derivation of the term.  Nomina dubia are 
taxonomic in any case, since they are valid under our taxonomy code, the 
ICZN.  Nomina nuda or specimen numbers aren't taxonomic, but both can still 
be OTU's because they're organisms.  Hell, even hypothetical or all-zero 
outgroups are OTU's, and they're not even really organisms.  If anything, a 
nomen dubium is more taxonomic than phylogenetic, since at least it has a 
distinct taxonomic identity, though lacking a distinct phylogenetic one.

> <Why view -idae and -ia clades differently if we're ignoring the ICZN?>
>
>   Who says we should ignore the ICZN?

Tim posed the possibility, in the text I included with my message-

"If we are serious about erecting definitions that are stable, then some 
time-honored traditions have to be compromised, ICZN or no ICZN.  
Ceratopsidae could become Centrosauridae, and Hadrosauridae could become 
Saurolophidae - but Ceratopsia and Hadrosauria would remain."

Why would Hadrosauria remain, but Hadrosauridae be discarded, if not for the 
fact ICZN rules don't cover suprafamilial level taxa?

Mickey Mortimer