Aves and stability (and general observations)

[Ken Kinman]

Dear All,
      I would like to thank Pierre for his excellent post (especially
raising the "stability" issue, which I will get to).  We have very similar
moderate views and get along quite well, but we are both aware that in spite
of the close proximity of our views, that we are still separated by this
wall of eclecticism vs. cladism.  I think we agree that the wall should be
torn down, but disagree on how to best do it.
      Pierre's suggestion is that we take a more cladistic approach,
formally classifying birds as dinosaurs, and calling the old paraphyletic
concept of dinosaurs by the informal phrase "non-bird dinosaurs".  This
seems like a good compromise solution in the short-term (I myself have used
the phrase "non-avian dinosaurs" in some contexts to assure that I am
understood).  However, I am convinced that it cannot work in the long-term.
I think Benton, 2000 (which we've discussed before) addresses some of the
long-term problems, and for those who haven't yet done so, I very strongly
recommend reading Eric Knox's 1998 paper (Biological Journal of the Linnean
Society, 63:1-49; entitled "The use of hierarchies as organizational models
in systematics").
      Now for the issue of STABILITY and how Aves demonstrates the problem.
I have been watching the bird-dinosaur debate for many, many years, and have
immersed myself more deeply into it for the past couple of years.  Let's
ignore the Feduccia minority viewpoint for now (which really makes things
complicated).   Even among the vast majority, who now agree that birds are
dinosaur descendants, there have already been endless debates over whether
mononykines are birds, or if Rahonavis is a bird, or Caudipteryx,
Protarchaeopteryx, Bambiraptor, Unenlagia ("half-bird"), Microraptor,
oviraptors, and so on (and then there's the Protoavis mess which is a story
unto itself).
     My contention is that much of this confusion and needless wrangling is
no longer due to the lack of information, but rather due to the use of
Archaeopteryx as the basalmost bird (the cladistic definition I have
accepted, up to now, for the sake of stability in the short-term).  But we
now have sufficient data to define Aves in a more scientifically rigorous
fashion (osteologically), just as was done with Mammalia decades ago.  The
presence of hair and lactation roughly correspond to the scientific
definition, so there have been no big problems reconciling the two
(communication went smoothly, at least until cladistic splintering muddled
it up with Mammaliamorpha and the like).
     The new definition of Aves, if done correctly, will do for birds what
has so long been successfully done with mammals.  The scientific definition
will be precise (osteological), but it will roughly coincide with the
presence of "vaned" feathers.  All those more primitive "protofeathers" on
Sinosauropteryx, the newly-discovered pterosaur, and even that
bristly-tailed psittacosaur, are apparently just that (PROTOfeather
homologs).
     In this context, the evolution of powered flight and brooding, the
ornithoid eggshell evidence, and so on, will begin to make more sense, and
it will clarify many of the debates that have paleontologists and
ornithologists insulting each other in the press and in other public forums
(fora?).  The whole Longisquama debate is one of the more embarrassing
episodes.
     I am proposing a long-thought-out, moderate paradigm shift that I
believe will enhance stability.  Both scientists and the public alike will
have to learn that the old "bird = feather possession" idea is inaccurate
and out-of-date.  But shifting to the possession of "vaned" feathers seems
the best way to accomplish a smooth transition.  What we now have is
confusion and taxonomic instability.  The question in my mind is not
*whether* we should draw a new line, but *where* it should be drawn.  To
continue drawing the line at Archaeopteryx (eclectically or cladistically)
is a tradition that I think we must abandon for everyone's sake.
     More generally, we are faced with a decision between:  (1) an eclectic
emphasis on apomorphy (character)-based taxa or (2) a purely cladistic
emphasis on node- and stem-based taxa.  The latter seems to sacrifice
stability of content in favor of stability of definition (definitions which
cladists are already fighting over, requiring a new bureaucratic code to
settle them, and no sign that its decisions will be followed anyway).
      If you look at it from a broad perspective, all classifications are
arbitrary and "typological" to some degree, and pure cladism is just
promoting a new form of arbitrary "typology".  Benton has already pointed
out that in the end, we will be no better off, and in many ways we will be
much worse off if we follow this path.  The pendulum has swung too far
already (swinging so far, that even I have been ousted from the "Cladists
Club", which is very odd because some eclecticists think I'm too much of a
"cladist").
            ------ Ken Kinman



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