RE: Birds and pornography and Caenagnathiformes (toothlessness)

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

Ken Kinman wrote:

>     And I was rather puzzled by Tim's post about Archaeopteryx and 
>Deinonychus being so much alike.  I agree that they are alot alike, so
>why object to putting them into the same Class Aves?  I even put
>Deinonychus in Order Archaeopterygiformes.

Two points:

(A) The concept of "Class" is seriously misguided.  (see below)

(B) _Archaeopteryx_ and _Deinonychus_ are indeed very much alike.  However,
it's only because you slide the definition of Aves down the  cladogram to
the "key apomorphy" of semilunate carpal (SLC) that _Deinonychus_ is in the
Aves.  Now, you have a different set of taxa on the threshold of Aves,
excluded from the Aves only because their carpal configuration doesn't
constitute a "true" SLC.  You see how arbitrary it is?  No matter what you
nominate as your "key apomorphy" you're faced with taxa that are on the
"fringes" of the Class - which defeats the purpose of having a Class in the
first place.  

Unlike Linnaeus, we now know that the morphological/physiological gulfs we
see between modern Classes are the result of divergence over very long
periods of time.  They aren't the result of a spontaneous act of Creation
(oh, perhaps combined with differential survival via a very large boat).

The fossil record tells us that the divisions between one Class and the next
disappear as you go back in time.  This undermines the very concept of a
"Class".


"Philidor" wrote:

>True:  go far enough back into the ancestry to creatures never seen >alive,
and you can find animals so like two groups that classification >is
arbitrary.  

No, this isn't what I said at all.  When two clades are sister taxa
separated by only a few (and perhaps only one) character, promoting one
clade to the rank of "Class" is completely arbitrary. 

>In Jefferson's wonderful phrasing, groups should be distinguishable at a 
>glance by a traveler on horseback.  

As David has said... One word: Vermes!

You can distinguish all the different groups of "worms" from horseback?
That would be extremely difficult - especially if the horse stepped on them.

I think you might be referring to vertebrates.  Even in this case,
your/Jefferson's comment ignores the basic evolutionary concept of
convergence.  You can distinguish a New World and Old World vulture by a
sidelong glance?  A thylacine and a wolf?  A caecilian and an amphisbaenid?

Are you certain that this story isn't apocryphal.

>He had real doubts about whether 
>skeletal information should be used in distinguishing groups, and I feel 
>sympathetic to his problem. 

Doesn't leave much to work with when examining fossil vertebrates.

>I can acknowledge your point, right up until you make the assertion that
>any view different from your own must be antiscientific because >inherently
based on obsolete notions of progress, superiority and >inferiority. 

Not "my own" view.  You can attribute the concept to evolution itself. The
"antiscientific" view is different from the way evolution works; it isn't
guided by "progress, superiority and inferiority." 


>Just please don't assert that the alternative is only wrong-headed 
>philosophical mush.  Doesn't seem very persuasive to me. 

Linnaeus' ideas were moulded by the times he lived in.  Why shouldn't our
ideas be shaped (and altered) by the knowledge we've gained over the past
200 years?




Tim