Re: TETRAPODS, PHYLOGENETIC TAXONOMY, AND CLEAR DEFINITIONS

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

I'll try and keep this one brief.

At 10:30 PM 7/23/98 -0400, Jonathon Woolf wrote:

>> This really was no different in the Linnean system.  We can consider a
>> taxon to have several properties:  name definition, diagnosis, group
>> membership, timing of origin.  The Linnean system effectively tried to
>> maximize the stability of the diagnosis, but diagnoses were still labile:
>> were we to diagnose Dinosauria on the basis of a perforate acetabulum and
>> inturned femoral head, and then discover some new fossil with one but not
>> the other, the diagnosis would still require modification.
>
>Would it?  If the diagnosis of Dinosauria is as you state, then an animal
must have
>both those features to be a dinosaur.

Ankylosaurs don't have a perforate acetabulum: they must not be dinosaurs
under your rules.

>Remember, I'm a programmer.  Boolean logic:
>(A AND B) is true if and only if A is true and B is also true.  (I'm sure you
>already know that, but an awful lot of stuff I've said lately has been badly
>misconstrued, and I want to avoid any more of that.)  If taxon M is
diagnosed by 22
>characteristics, and organism X has 21 of those characteristics, then X isn't a
>member of M.

Ankylosaurs aren't dinosaurs, whales aren't tetrapods, kiwis aren't birds.

You're a programmer: great.  However, we are talking about organisms which
have a history of descent with modification, not software written from scratch.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661