Message 2002-04-0018: genus definitions

Tue, 30 Apr 2002 11:33:53 -0700 (PDT)

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Date: Tue, 30 Apr 2002 11:33:53 -0700 (PDT)
From: "T. Michael Keesey" <>
To: Mailing List - PhyloCode <>
Subject: genus definitions

(I hope I haven't mentioned this here before.)

I was thinking about the styles of clade definiton available other than the
typical node-, stem-, and apomorphy-based ones, and wondered if something in
this style might be possible, or even wise, for converting genera:

"Type species _x_ Author year and all species sharing more recent ancestry with
_x_ than with any other species designated as the type species of another

As an abbreviated notation, I might suggest Clade(type _x_ <- other types).
(Anyone care to translate that to Latin?)

Note that if two clades were defined in this style based on what turned out to
be synonymous species, they would be heterodefinitional synonyms, the clade
named first would have precedence, and the type species of the clade named
second would cease to be considered a type species. (I think.)

In the next version of my website (The Dinosauricon -,
I don't want to distinguish between genera and clades. The problem is that very
few dinosaurian genera have been cladistically defined (the only example I can
think of is _Archaeopteryx_, IIRC, and that was problematic - more below). So I
was planning to temporarily use this method of definition. (Emphasizing that it
was only temporary and not published or official in any way.)

I think it works pretty well, except for one or two pitfalls. One is that I
need to arbitrarily suppress some generic names which are not commonly used.

Another odd thing about it is that content can change if a species formerly
within such a clade is designated the type of a new clade. This could be
beneficial, such as in the case of _Archaeopteryx_. _Archaeopteryx_ was, IIRC,
defined as Clade(_A. lithographica_ <- _Neornithes_), but this may include such
diverse forms as the large, flightless _Unenlagia comahuensis_ and the
sickle-clawed _Rahonavis ostromi_, which would go against the decades-old usage
of _Archaeopteryx_ for a group of flying, non-sickle-clawed primitive birds.
But with this style of definition, _ostromi_ and _comahuensis_ could be
designated as types of their own clades, and thus excluded from

On the other hand, this could be abused if, for example, someone decided to
make _Homo neanderthalensis_ the type of a new clade, thus excluding it from
_Homo_ AND excluding _erectus_, _habilis_ etc. from any clade more specific
than _Hominina_. Just as it could be used to preserve stability (as in the
_Archaeopteryx_ example), it could be used in a destabilizing manner.

Thoughts? Like it? Hate it? Know how it could be improved? Think it doesn't
merit improvement? I'd like to hear.

=====> T. Michael Keesey <>
=====> The Dinosauricon <>
=====> BloodySteak <>
=====> Instant Messenger <Ric Blayze>

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