Re: seeking clarification on the cladism debate (RE: hidden "cladistic" ranks)

["T. Mike Keesey" <tmk@dinosauricon.com>]

On Thu, 18 Oct 2001, Ken Kinman wrote:

>      If I understand David's question correctly (about "setting points"
> along a phylogeny), this is precisely what I do in my classifications.
[...]
>       At such a "re-setting" point, a divergent and rapidly evolving taxon
> is bumped up a rank (sometimes even more than one rank).

The problem with this is that as new discoveries are made, what once
seemed a divergent taxon no longer looks as unique. A great example is
_Aves_. When the taxon was first named, they seemed like a very different
group from other amniotes. Then _Archaeopteryx_ was discovered, which
filled in the gap a bit more. Then more and more discoveries were made,
until now we have a far more fine-grained morphological series leading
from primitive avians back to primitive dinosaurs and beyond.

"Classogenesis", "Ordogenesis", etc. are not things that really occur in
nature. Evolution does not occur by occasional gigantic leaps but by the
accumulation of smaller changes (the rate of these changes may vary, but
they are still small). The hallmarks of "bird-ness" did not occur in one
speciation event, but over millions of years in gradual steps. The
decision to split off a new Classis with _Archaeopteryx_ and "higher"
birds is an artefact from the history of paleontology, and has nothing to
do with reality.

Put another way, I find it quite ridiculous to include _Microraptor_ in a
taxon that includes _Diplodocus_ but not _Archaeopteryx_. How is that
useful at all?

>        I therefore completely disagree with Mike's statement that nesting a
> higher ranked taxon in one of lower rank renders such ranks meaningless

But your system does not really place taxa of higher ranks into taxa of
lower ranks. The connections are made in the diagrams, but when using the
taxa in prose, these connections vanish.

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T. MICHAEL KEESEY
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