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Re: Nitpicky cladistics



At 11:52 AM 11/17/96 +1030, you wrote:
>This comment by Tom Holtz (11/15/96; 10:06a) intrigues me:
>
>>The word "Maniraptora" BY DEFINITION includes the birds!
>
>It is my sense that birds have not been conclusively shown to be
>descended from deinonychids or any other dinosaur.  So, since we can't
>demonstrate it by the evidence, can we really get around that by DEFINING
>it to be the case? (Yes, I know the prevailing opinion in this group, but
>my question is conceptual.)

Reexamine Gauthier 1986.  Maniraptora is *NOT* a dinosaur group that may
include birds, it is a bird group which may (or may not) include certain
dinosaurs.

It is a taxon defined as birds and all taxa closer to birds than to
Ornithomimus.  It probably includes dromaeosaurids, maybe oviraptorids,
maybe others; but if birds are crocodile descendants, the it includes crocs
but does not include any dinosaurs.

>Wouldn't a non-cladistic taxonomic category still exist if part of it
>were removed?

But the name Maniraptora was coined SOLEY for use within cladistics.

>>If you choose not to use a cladistic taxonomy, then please do NOT use
>>the word "maniraptor".
>
>What happens to maniraptor if you use cladistics to make a case that
>birds are descended from an ornithosuchian?  (Granted, that would require
>some new fossils to be found, but, again, the question is conceptual.)

Then ornithosuchids are members of Maniraptora and no dinosaur would be.

>I
>assume one could define a new cladistics-based category, perhaps the
>"Thecoavia" or even "Ornithornithia," which, BY DEFINITION would include
>birds.

One could.  If one were following the system of phylogenetic taxonomy,
however, then Maniraptora would have priority.

>Cladistics-based taxonomic categories seem poised to dictate our concepts
>of reality, whereas it should be our concepts of reality that dictate the
>taxonomic categories.

Not at all.  Your above example shows how this term would be used if new
evidence pointed to a different origin of birds.

Taxa in the phylogenetic taxonomic system (not phylogenetic systematics per
se, but the system of taxonomy developed by de Queiroz and Gauthier) are
defined by ancestry (all taxa sharing a more recent common ancestor with X
than with Y, or all descendants of the most recent common ancestor of X and
Y), NOT by traditional content (i.e., "maniraptors" for dromaeosaurids,
oviraptorids, troodontids, etc.) NOR by diagnosis (i.e., "maniraptors" for
all taxa with a fully-developed semilunate carpal block).  It is a really
different method of taxonomy, but one which is gaining support throughout
the systematic community.

>Cladists have become prisoners of their own rules.

Not at all.  See avoe.

> Non-cladistics-based taxa are superior from the standpoint of not
>requiring any particular view of the course of evolution to be valid.
>Perhaps "bird" should be kept separate, being descendants of maniraptors
>(defined differently).

"Birds" remain their own unit, regardless of what else is within Maniraptora.

>
>Maniraptora seems to be a legitimate grouping of dinosaurs, whether one
>uses cladistics or not, or whether birds are included or not.

Indeed.  However, no one until Gauthier seems to have recognized that,
although some (Ostrom, Bakker, Padian, etc.) got close!

>So, any
>non-cladist ought to be able to use it.  It's not a forbidden term for
>them.  They might have to redefine it, but that happens all of the time
>in taxonomy.  No reason why it can't happen to terms established by
>cladists.
>
>Have I missed something here?    :-S ?

Perhaps you could read the work of de Queiroz and Gauthier (most recently in
Trends in Ecology and Evolution, 1994) demonstrating the principles of
phylogenetic taxonomy?

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

"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
        --O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877