Re: Evolution:Small Scale/Grand Scale

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>I don't mean to sound flippant, but how far can you carry such cladistic
>logic?  In theory, there is only one clade: Protozoa; we're demonstrably all
>descendants of some Urprotozoan, right?  Obviously, you wouldn't carry the
>process to such an extent, but where *do* you draw the line?

Incidentally, even most "gradist" microbiologists have dropped the term
Protozoan, and prefer Protoctista.

Microbiologists have recognized that some single-celled organisms share
more derived characters with Plantae, others with Fungi, and still others
with Animalia.

Under a strictly phylogenetic taxonomy, NO paraphyletic names are not used
(such as Protozoa or Invertebrata). {Actually, Invertebrata is a great
example - no reasonable modern systemicist, cladist or otherwise, argues a
group which includes all metazoans except vertebrates.}.

To answer you question, the line would never be drawn under a strictly
cladistic taxonomy.  So, instead of both "Protozoa" (= all single-celled
nucleated organisms) and "Eukaryota" (=all nucleated organisms), only the
second (a monophyletic group) would be used.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist                           Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.