Birds and pornography

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Ken Kinman wrote:

>(regardless 
>of whether you want to call Aves a major "Class" or a major "Clade"---to
>a cladisto-eclecticist, Aves is both a Clade *and* a Class).
    
I know many of my responses to Ken sound horrible and mean - and I hope
nobody (least of all Ken, who I have enormous respect for) interprets them
as *personal* attacks.  However, the idea of "Classes" is a pet hate of
mine, so it tends to arouse a lot of passion on my part.

First off, the "cladisto-eclecticist" Kinman-ian scheme is not eclectic at
all, since rather than combining the best of cladistic and Linnaean
taxonomies, it combines the worst of both systems.  "Cladisto-eclecticist"
retains the baggage of the Linnaean system (with its attendant assumptions
of "progress") and lacks the explicitness of phylogenetic systematics.  

In days of yore, taxonomic nomenclature (especially the erection of Classes)
reflected a hierarchial view of Nature that was heavily influenced by
religious doctrine.  That mindset is reflected in certain names: Reptilia
("crawling things") and Primates ("foremost") are good examples.  With the
acceptance that evolutionary change was responsible for the observed
diversity of species, the Linnaean system was absorbed into an evolutionary
framework.  However, the concept of "Class" was retained as part of an
undertow of "progress" that permeated the concept of evolutionary change.
Birds got their own "Class" because (like mammals) it was believed that they
had transcended the "lowly" grade of Reptilia.

This concept is flawed.  Further, features that were were once used to
separate birds (Aves) from reptiles - furcula, feathers, wings, endothermy,
etc - are either not directly discernable in the evolutionary history of
birds (endothermy) or arose far deeper in theropod phylogeny (feathers,
wings, furcula), or both.  Therefore, Ken (and others) are searching
cladograms high and low in a quest to find an alternative evolutionary
novelty that can be used to define "Aves".    

The amount of time and effort that Ken has invested in this quest should
immediately tell you that birds are not so different from their ancestors,
and that the distinction between Aves and non-Aves is (despite what Ken
says) entirely arbitrary.  The long list of features that make modern birds
so different from modern reptiles arose not through a single transformation,
but through a gradual cumulation of many characters extending over a hundred
million years (give or take).  As one list member is fond of pointing out, a
pigeon looks very different to a snake.  However, _Archaeopteryx_ "looks"
strikingly similar to _Deinonychus_, therefore underming the "pornographic"
definition of a bird: difficult to define, but I know it when I see it.

Ken has chosen the appearance of the semilunate carpal (SLC) as the dividing
line between Aves and non-Aves, under the twin assumptions that (1)
ecomorphologically the SLC represents a salient "turning point" in theropod
evolution; (2) the appearance of the SLC is "clear cut" and precise.  (1) is
a subjective interpretation of the fossil record, and (2) is dead wrong, as
the available fossil evidence makes obvious.  Neither assumption can be
upheld.

The take-home message: Dump the concept of "Class" like a dirty diaper.  



Tim