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Re: Cladistics and names



At 05:25 PM 5/14/97 -0500, you wrote:
>Ok, this isn't really a dino question.  Sue me. But with all the
>cladistics discussed here, I figure someone can help me out.
>
>It has been mentioned that the "rank" concept in Linnean taxonomy gets
>pretty much tossed by the wayside in cladistics.  Ok, I can deal with
>this looking at the blizzard of names that "pure" cladistics creates (as
>a fault with the system, this is a REALLY minor quibble so if this
>comment has annoyed you, chill).  However, the rank system did have the
>advantage in that you could tell in most cases what level in the
>hierarchy a name referred to by its ending; for example, -idae was for
>families as everyone here I am assuming is well aware.

Please note: ONLY the family group (family, subfamily, tribe, subtribe, and
superfamily) had a specific suffix (-idae, -inae, -ini, -ina, and -oidea,
just to be explicit) within Linnean systematics.  Of these, ONLY the family
was an obligate name (that is, a family was required for a taxon, but the
other ranks were only supplied if there were a sufficient number of closely
related forms to justify creating the extra names).

For particular taxa, there were traditional suffices for other ranks (e.g.,
-iformes for bird orders, -ida for some invertebrate orders, etc.), but
these were not standardized (any more than the ending -mimus is required for
new ornithomimid genera: it is traditional, but not required).  Non-tetrapod
osteichtyians (classic "bony fish") have suborders ending in "-oidei", while
chondrichtyians (sharks, rays, and their relatives) have traditional
suborders ending in "-oidea".

So, except for the family group, you couldn't tell from the ending where
different taxa fit in the hierarchy relative to each other.  Quick, without
checking, where do the taxa "Cytheracea", "Ostracoda", "Podocopida",
"Maxillapoda", "Panarthropoda", "Crustacea", and "Protostomia" fit relative
to each other?  What rank is the "Taxodonta"?  

Taxonomy always required more than a modicum of reference to tables (and,
with time, memorization).  Cladistics doesn't change any of that.

>But with the
>loss of the ranks, how do you handle the endings you place on names and
>is there any way at all of having some idea where in the structure a
>group name is without having access to the particular cladogram being
>used by the person who mentioned the name?  All the references I have
>read on this were either as clear as mud or mimiced english in that the
>exceptions were far more common than examples that followed the rule.
>
>Anyone who can help to clear up this little bit of confusion will be
>held in high esteem.

As I noted above, the idea that classic Linnean taxonomy had some special
information retrieval abilities lacking in cladistics is a strawman
arguement.  With the exception of the family rank (coined by taking a type
genus and a specific ending), Linnean names did not have specific special
clues in them revealing where they fit in the hierarchy.  WITH USE, people
became familiar with the traditions within their particular clade of study,
but the traditions were different for each taxon.

So, in that sense, cladisitics doesn't change anything: it still requires
reference to a table, cladogram, or what have you.  However, a side branch
of cladisitics called "phylogenetic taxonomy" allows explicit definitions of
clades.  For example, "Iguanodontia" can be defined as "Iguanodon and all
taxa sharing a more recent common ancestor with it than with Hypsilophodon".
The emphasis is on an ancestor-based definition rather than a metaphysical
concept of "rank".  Even as our cladograms change, and taxa move in and out
of position relative to Iguanodon and Hypsilophodon, there will always be a
clade composed of Iguanodon and all taxa more closely related to it than to
Hypsilophodon, so the taxon "Iguanodontia" will remain.

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