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Re: Lumping Spinosauridae Redux



--- "Jaime A. Headden" <qilongia@yahoo.com> wrote:

> Mike Keesey (mightyodinn@yahoo.com) wrote:
> 
> <At what time? Sorry, I still don't follow.>
> 
>   I was hoping my allusion to crowns would have simplified this. I meant,
> "all valid type species considered at the time the clade name is defined
> and described..."

Oh, okay, gotcha. No, that would be a bad idea. For example, _Iguanodon_ would
equal _Ornithischia_ (and _Lemur_ would equal _Strepsirhini_, _Vespertilio_
would equal _Chiroptera_, etc.)

> <No, _Suchomimus_ would be a clade and _walkeri_ a species. Different
> types of taxa.>
> 
>   As described below and elsewhere, these mean essentially the same thing
> in some circumstances and ... 

On occasion they can have the same membership, but they are not the same thing.

>a species can be considered a clade,
> comprised of internal specifiers (as a stem including the type specimen),
> or a crown, or a node (of all individuals), or even a stem-defined node
> (all individuals of the given type that share a relationship that does not
> include, say, the type of another species).

Only terminal species (those with no descendants) can possibly be equivalent to
clades (albeit differently defined). All others (which is most of them) are
paraphyletic, and hence not clades.
 
> <If _Suchomimus_ = genus(_tenerensis_), _Baryonyx_ = genus(_walkeri_), and
> _tenerensis_ = _walkeri_, then it follows that _Suchomimus_ = _Baryonyx_.>
> 
>   This would only be true, in my opinion, if one could determine that
> *tenerensis* = *walkeri,* which I contend is not likely to be absolutely
> provable. Whatever their synapomorphies, their differences may be
> considered "specifically" separatable, given one worker or another.

Yes, that part of it is subjective, as it stands. (Hence it is a *provisional*
system.)

> <But the provisional definitions rests on species, not on specimens. I
> think that's what you're missing.>
> 
>   I think I get that. The species are defined on specimens, and the genera
> are defined on their type species. If one treats this as a continuum, and
> every named genus as a clade, then all further internal bifurcations or
> lineages are also clades. One may also assume that if a genus is defined
> by a species that is defined by a specimen, then the genus can be thought
> to be essentially tied to the specimen, and the species is an intermediate
> "clade" or organism, or category.

A species is not a clade or an organism.

> If a "genus" clade can be anchored on a
> species, and it is found that the specimens of two relatively close
> species would be sister-taxa (or synonyms), they are each still the type
> specimens of species that are defined by mutually excluding one another,
> and thus as species defined by mutually excluding one another. Their
> definitions as offered do NOT permit synonymy at the "genus" level, so
> *Suchomimus* will never be a synonym of *Baryonyx.*

You are viewing this at the level of individual organisms, which I do think is
a more rigorous way to do it, but my provisional system rests on species, not
individual organisms, and species may be synonymous. If two different genera
are typified by species that are considered synonymous, then the genera are
considered synonymous.

If you want to propose a system that rests on individual organisms as opposed
to species, then more power to you (and, while you're at it, give me a hand,
because I'd like to do the same thing), but don't claim that my provisional
system does so.

This is probably getting off-topic.

=====
=====> T. Michael Keesey <http://dino.lm.com/contact>
=====> The Dinosauricon <http://dinosauricon.com>
=====> Instant Messenger <Ric Blayze>
=====


                
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