non-linnean systematic & taxonomic authoritarianism, the meanings of parsimony, and the origin of birds

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

Greetings,

A few thoughts on various recent topics:

Linnean taxonomy:
* Although lower-level Linnean taxonomy ("genus", "species", and the
post-Linne rank "family") were largely accepted throughout the scientific
world in the late 1700s onward, higher level Linnean systematics and
taxonomy was not.  Please do not confuse the widespread acceptance in the
20th century as evidence of earlier "universality".  For example, the
"Quinarian" system (which postulated a five-fold division at all levels of
taxonomy) was accepted from people ranging from the anti-evolutionary
anonymous author of "The Vestiges of Creation" to good old Seeley, coiner of
'Saurischia' and 'Ornithischia'.

* Additionally, even for those who used Linnean taxonomy there was certainly
no more concensus among the details of the taxonomic arrangements of a
particular group between workers than there is between two alternative
cladograms today.  This is a time to set down your Romers and Simpsons and
other textbooks, and look at the technical taxonomic literature of the late
19th and 20th centuries to see how really, really different the taxonomies
of two different workers could be! (This raises the further problem, already
noted, as to how a third party would choose between the two alternative
taxonomies: what criterion or criteria should they use?).

Meanings of "parsimony":
* Some recent posters have been conflating (understandably so) two different
uses of the word "parsiomony".  Broadly defined parsimony = Ockham's razor
(preference for chosing the simpler of two alternatives so as not to
multiply assumptions or entities unnecessarily).  Narrowly defined, in the
computational aspects of systematics, parsimony (or more technically
"maximum parsimony") is one of several different possible means of choosing
between alternative character state changes and trees in an analysis.  Other
methods, such as maximum likelihood, rely on various additional data
(probablistic or biochemical arguments of the differential ease of
transcription rather than translation, etc.).  Note that these other methods
**ARE** parsimony arguments broadly defined: that is, they choose the
simplest explanation; however, the means of measuring simplicity is
different.

Origin of birds:
* The statement that the origin of birds is still in question is getting
rather tired, and quite frankly unsupportable.  The ideas that birds lie
outside Theropoda is of equal merit based on the anatomical evidence that
titanotheres lie outside of Perissodactyla.  Yes, one can argue that there
are some molecular or developmental clues which are totally inaccessible
(given the absence of such data for non-avian theropods or for titanotheres)
which would overturn these positions.  However, based on the known anatomy
of the taxa in question these placements are highly, highly supported.
        Some may still be uncomfortable with this discovery, but I think this 
has a
lot more to do with emotions and preconceptions than it does with data.  By
this I mean that had the evidence pointed to origin of birds within
drepanosaurids or choristoderes or procolophonians or some other group of
extinct reptiles with no popular fan base, and indeed no popular knowledge,
that we wouldn't see the sort of resistance as we do to the discovery of
birds as living descendants of the most popular group of fossil reptiles.

Take care,

                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