The nature of cladistics (for the "younger" biologists)

Ken Kinman kinman2 at YAHOO.COM
Sat Nov 20 11:22:06 CST 2004


Dear All,
     The reason flight feathers are so important to me is because they've been so particularly important to the birds themselves, triggering their enormously successful evolutionary radiation into new niches.  Thus they are also particularly important to all the organisms that interact with birds (chasing them as prey, being preyed upon by them, being pollinated by them, scattering seeds to new places, and so on).  3- vs. 4-chambered hearts are important, but not THAT important (even if they did fossilize well).   What we now need to do is to zero in on certain skeletal synapomorphies (more easily preserved in fossils than are feathers) which arose in concert with flight feathers.  With all the new Chinese fossils coming out, such skeletal synapomorphies should become increasingly apparent in the near future.  Naturally they center on the arms (wings), shoulders, and chest area (while in mammals they were found in the fast-evolving jaw articulation and ear ossicles).

     Anyway, for all those "impressionable" young biologists out there, you don't have to choose between just the two extremes (the old inexplicit paraphyly and a strict cladism that eliminates paraphyly altogether).  We can forge a new classificatory synthesis, taking a middle course that incorporates the good aspects of both extremes (and rejects the harmful aspects of both).  The reptile classification which I presented here in April is just one example which balances the old and the new, reflecting new knowledge without bulldozing down the old, and without unnecessary confusion and putting a lot of people off with a new, burgeoning classificatory "legalese".   Formally naming every clade should be discouraged, not encouraged (and many don't turn out to be holophyletic anyway).

      Reptile evolution and classification is extremely difficult and controversial, but it doesn't have to be completely cladified into something that is becoming increasingly incomprehensible (and is getting worse).  I will be inserting major new plesion taxa when necessary and tinkering with the cladistic coding to reflect up-to-date topologies, but I plan to be using this basic classification for a very long time (see below).  FINAL NOTE:  I think it is pretty clear that I love cladistics and milking out all the phylogenetic goodies I can, but strict cladism blindly denies that limited paraphyly can further enhance classification with a lot more stability (where information is lacking) and additional anagenetic information (formally marking major synapomorphies like flight feathers).  They've thrown a baby out with the bath water, hurting not only the rest of us, but also damaging their own goals in the long term.

CLASS REPTILIA%%
    1  COTYLOSAURIA% (primitive reptiles)
          1  Diadectiformes
          2  Pelycosauriformes%
         _a_ Therapsiformes%
         _a_ {{Mammalia}}
          3  Mesosauriformes
          4  Millerettiformes
          5  Procolophoniformes
          ?  Testudiniformes
          6  Plesion Captorhinidae
          7  Plesion Protorothyrididae
          8  {{Diapsida}} (= Lepidosauria
                     plus Archosauria)

    _1_ LEPIDOSAURIA% (basal diapsids)
          1  Araeosceliformes
          2  Plesion Coelurosauravus
          3  Plesion Apsisaurus
          4  Younginiformes
          5  Eolacertiliformes
          B  Sphenodontiformes
          C  Squamatiformes
          6  Ichthyosauriformes
          B  Sauropterygiformes
          ?  Thalattosauriformes
          7  Choristoderiformes
          8  Trilophosauriformes
          B  Rhynchosauriformes
          9  Protorosauriformes
         10  Proterosuchiformes%
         _a_  {{Archosauria}}

    _1_ ARCHOSAURIA% (ruling reptiles)
          1  Suchiformes% (basal crurotarsans)
         _a_  Crocodyliformes
          2  Plesion Scleromochlus
          B  Pterosauriformes
          3  Dinosauriformes%
         _a_  {{Aves}}

_a_ CLASS AVES

_b_ CLASS MAMMALIA

-------------------------------------
Paraphyly is explicitly shown:
   %% (doubly paraphyletic taxon)
   % (singly paraphyletic taxon)
   _1_ and _a_ are exgroup codings




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