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RE: New Dinosauricon Taxon Pages: _Therizinosauria_



(Copying to PhyloCode list.)

--- aegyptiacus@aol.com wrote:
> Mike, it seems your new Therizinosaur's page has aroused many comments. But
> it remains excellent nonetheless,

Thanks!

> as long as it promotes dialogue.

I'm glad it has! (Even a heated exchange is better than none at all.)

> If I'm not mistaken, some problems come  from clades being named after genera
> names. Nobody would say a word about Arthropods, as there's no animal called
> Arthrtopod_what_you_want_here, or insect_ending_, or mammal_ending_, or
> reptilia_ending_ and I could go on. That is, associating a clade with a genus
> just by name (like poor _Megalosaurus_) seems to be a problem to keep the
> stability in *definition*. If tyrannosaurs were members of a clade called
> *anything_but_tyrannosaur_rooted_name*, there would be no problem to move
> them around cladograms.
> Or am I missing a point?

I probably need to mention this on a more apparent section of the site, but see
here: http://dino.lm.com/terms/display.php?name=Genus

"Provisional Usage: This version of The Dinosauricon adheres to Draft
PhyloCode's philosophy that all taxa must be either clades or species. Genera
are provisionally converted to stem-based clades, including one internal
specifier (the type species) and having all type species of other genera as
external specifiers."

So, in essence, when I write a definition's formula as "Genus(_species_)", it
really means "Clade(_species_ <- all other specifiers of
genera/generically-defined clades)". The programming behind the Dinosauricon
automatically assigns these to stems on the cladogram and can even find
heterodefintional synonyms among "non-generic" clades (e.g., _Alxasauridae_ ==
_Alxasaurus_, at least until a new alxasaurid genus is named).

When I originally implemented this, I thought I would have to provisionally
suppress some genera to prevent oversplitting, but now I don't think that's
necessary. For Mesozoic dinosaurs, at least, it seems to work fairly well.

Thus _Megalosaurus_ becomes Clade(_bucklandii_ Ritgen 1826 <- all other type
species), which is fairly stable, I think.

There are, of course, some problems, which is why I emphasize that it is
provisional:

1) Instability. Whenever a new genus/generic clade is named, another
genus/generic clade's content may be affected (it may shrink). Of course, this
is a problem in Linnaean taxonomy as well.

2) Some species will be left without genera/generic clades. I don't really
think this is a problem, but it is inconsistent with common usage, which may
cause some to balk. (Depends on your personal taste for name lists like, e.g.,
_Therizinosauria_ _bohlini_.)
One interesting example:
  --+--_belli_ (type of _Chasmosaurus_)
    |--_russelli_
    `--+--_mariscalensis_
       `--_sternbergi_ (type of _Pentaceratops_)
Traditionally, the first three are referred to _Chasmosaurus_, but the above
phylogeny (proposed, but not uncontested, AFAIAA) yields:
* _Chasmosaurus_ _belli_
* _Chasmosaurinae_ _russelli_ (no genus!)
* _Pentaceratops_ _mariscalensis_
* _Pentaceratops_ _sternbergi_
Personally, I'm comfortable with this sort of thing, as the assignments are
being made based on phylogeny, not opinion, and since, under this system,
genera aren't really genera any more, but clades, and should be treated no
differently. Others may not be comfortable, but hopefully they can see the
logic.

3) As with any stem-defined clades, they may collapse. An example I gave in an
earlier post is suitable here: if _Ursus_ = Clade(_arctos_ Linnaeus 1758 <- all
other type species) and _Thalarctos_ = Clade(_maritimus_ Phipps 1774 <- all
other type species), then _Ursus_ ceases to be recognizable as a clade, since
_maritimus_ (a type species) is descended from _arctos_.

=====
=====> T. Michael Keesey <keesey@bigfoot.com>
=====> The Dinosauricon <http://dinosauricon.com>
=====> BloodySteak <http://bloodysteak.com>
=====> Instant Messenger <Ric Blayze>
=====

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