Re: Dodson article

["Tim Williams" <twilliams_alpha@hotmail.com>]

Mike Nathal wrote:

> > In the latest issue of American Paleontologist,  Peter Dodson has an 
> > article about the symposium on "The Evolutionary Origin of feathers" held 
> > in Jan 1999 in Denver, the proceedings recently puplished in American 
> > Zoologist.    He comes out pretty strongly against cladistics and 
> > questions the theropod ancestry of birds.

OK, I'll bite.

Dodson must have changed his mind over the last twelve months.  In his 
_American Zoologist_ article (Amer. Zool. 40: 504-512; 2000), he says "My 
own position is that there is every reason to believe that the ancestors of 
birds was a small coelurosaurian dinosaur. (p.505)"  And, on the same page: 
"It is probably fair to say that the bird-theropod link is as firmly 
established as any phylogenetic link could be..."

The American Zoologist article is very interesting, and I thoroughly enjoyed 
it.  (I haven't seen the American Paleontologist article which Nathan refers 
to.)

Dodson certainly blasts cladistic methodology, claiming that it 
overemphasizes morphological characters at the expense of ecological, 
biomechanical and molecular considerations.  In particular, Dodson launches 
a rocket at the principle of parsimony, based on his own profound 
philosophical objections (poor old Popper gets hauled over the coals).  In 
its implicit denial of the "prodigality" of nature, Dodson even likens 
cladistics to Calvinism!

Dodson also objects to cladistic methodology on the basis that it is 
unnecessarily complicated and technocratic.  (I'm sure that will strike a 
chord with at least one member of this list.  ;-)  )  In Dodson's words, 
cladistics merely "confirms the obvious."  He puts forward the Ceratopsia as 
an example: his own morphometric analysis of phenetic data generated a tree 
that is remarkable congruent with a phylogeny obtained by cladistic 
analysis.  Dodson phrases this as an objection to cladistic analysis.  Other 
paleontologists might interpret this comparison a little differently.  A 
cladistic analysis might be seen as a more rigorous way of achieving the 
same goal - sifting out the primitive and convergent characters from the 
useful (shared derived) ones, which are used for constructing a phylogeny.

On the whole, I think Dodson's misgivings about cladistics are not too 
different from those expressed by John Ostrom.  I haven't heard Ostrom 
object to a theropod origin of birds lately...  :-)

By the way, opponents of a theropod origin of birds will draw cold comfort 
from Dodson's references to the origin of birds.  For example: "Today the 
fossil record strongly indicates that there is no credible evidence of birds 
prior to the Late Jurassic, when _Archaeopteryx_ appeared." (p.509; _Amer. 
Zool._ 40_504-512.)

(Dodson mentioned this to counter the claims of cladistic workers that bird 
ancestors might be found in the Cretaceous.  In an entirely literal sense, 
Dodson is entirely correct.  However, this is a slight misinterpretation of 
the inferred phylogenetic position of theropods such as dromaeosaurids and 
_Sinosauropteryx_, and perhaps overlooks the distinction between "sister 
taxon" and "ancestor".  Also, I'm reminded of Van Valen's comments about the 
first bats: bits and pieces of small Paleocene placentals - jawbones and the 
like - might actually belong to bats, but they cannot be classified as such 
until they turn up associated with identifiably chiropteran postcranial 
material.  For an early bird, unless a skeleton is found complete and with 
feathers attached, it may go unnoticed as a bird.  This is one problem that 
cladistics aims to overcome.  It is also the type of example which reveals 
the weakness of a methodology that depends too much on biomechanical and 
ecological assumptions about how flight evolved in birds.  In his thoughtful 
discussion of the topic, Dodson does not subscribe to this approach either.)

Tim



------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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