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Re: Classification: A Definition



On 5/25/07, Botterweg, Rrp <ronald.botterweg@capgemini.com> wrote:



All this brings me to the following observation (maybe an open door, in that case apologies):

there *IS* a need for ranking, also within phylogenetics/cladistics, but this 'ranking', or rather hierarchy ('vertical'), is strictly within the same tree, i.e. no comparative ranking.

But all organisms (all known ones, anyway) are in the same tree (well, same acyclic digraph, of which many subgraphs are trees).

Hence the temptation to use the familiar but misleading taxonomic naming 
conventions (-ia, -idae, etc.), which suggests non-existent comparative 
('horizontal') ranking, whereas they are just meant to indicate relative 
hierarchy (vertical levels) 'going down' one and the same tree.

There should be, and maybe there is within PN and I am just not aware of it, a clear and consistent methodology to indicate this hierarchy, without suggesting a 'traditional' comparative taxonomy, i.e. Clade Level1, Clade Level2, Clade Level3, etc. Obviously the number of levels and names may become huge, theoretically infinite. And at the genus and/or species level, I would suggest maintaining those as 'traditional' taxa, perhaps also giving the chosen genus/species concept.

But the way clades are defined does not allow for a name to be consistently associated with a particular rank. Consider:

- _Avifilopluma_ = Clade("panavian feathers*" in _Vultur gryphus_)
- _Maniraptoriformes_ = Clade(_Passer domesticus_ + _Ornithomimus velox_)

* hollow-based, filamentous, epidermal appendages produced by
follicles as found in members of Clade(_Vultur gryphus_ <--
_Crocodylus niloticus_)

We have no guarantee that one is inside the other, or even that they
are not the same thing. Based on our current knowledge we can't say
which one includes the other, or even if one is entirely included by
the other.

Furthermore, as hinted above, not all of life fits neatly into a tree
pattern. Clades may overlap without including each other.
Hybridization is a good example of this. Any pairs of reciprocal
branch-based clades among sexually-breeding populations are
potentially overlapping as well.

--
Mike Keesey