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RE: Ave Maria



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> zone65@bigpond.com
>
> It doesn't, but what is Aves now if it isn't a class?

It is a clade: an ancestor and all of its descendants.  So is any given
subset of Aves (Coraciformes, Galloanseres, etc.), and so are any of the
clades that contain Aves (Theropoda, Dinosauria, Reptilia, Vertebrata,
Eukarya, etc.).

Check the dinosaur mailing list archives for a great many discussions of
"rank" and "rank concept" in the past.  For the short form:
        Ranks add no definite information beyond what is already recognized for 
the
taxon itself, as "ranks" are not truly equivalent between clades. For
example, in what meaningful way is the "Class" Aves the equivalent of the
"Class" Bryozoa or the "Class" Insecta? Diversity (number of species)? No,
they are different by orders of magnitude. Duration (time of origin)? No,
these are all radically different. Amount of morphological disparity? Nope,
that doesn't work either.

Ranks were no more than a bookkeeping device in the early days of Linnean
taxonomy, back when the task of taxonomy was simply to lump critters into a
specific set of groups. With the recognition that evolution is the basis for
these groups, and the recognition that there are important groups to be
found between the traditional "ranks", the utility of the rank concept is at
an end.

Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796