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Re: cladistics (not a rant:)



Responding to a previous message by Nick Longrich:

>       As I understand it, Maniraptora is the sister group of
>Arcotmetatarsalia in a stem-based cladistics (or maybe it's not stem based
>but it isn't character-based) although Holtz 1994 uses Maniraptora to
>include both- am I right in assuming both these were character-based and
>are now stem-based?

Since I know something about this subject... :-)

I)  Maniraptora was coined by Gauthier, published in 1986, and defined as
"birds and all theropods closer to birds than to Ornithomimidae".

II) During the late 1980s and early 1990s, people tended to pay more
attention to the diagnostic characters of Gauthier's Maniraptora rather than
its defintion.

Thus...

III) I, in the 1994 paper, used "Maniraptora" for that part of the theropod
clade which was diagnosed by most of the manual characters which Gauthier
used to diagnose Maniraptora.

This.  Was.  Wrong.  I made a mistake.  So sue me... :-)

Anyway,

IV) Kevin Padian (not, incidentally, Gauthier's graduate advisor) called me
on my error: I had paid more attention to Gauthier's diagnoses than his
definition.  So, in order to fix my error:

V) Holtz, T.R., Jr.  1996.  Phylogenetic taxonomy of the Coelurosauria
(Dinosauria: Theropoda).  Journal of Paleontology.  536-538.

In this paper, I recognize the proper definition of Maniraptora, correct the
rather vague definition of Arctometatarsalia (now the sister group to
Maniraptora, i.e., Ornithomimus and all taxa closer to Ornithomimus than to
birds), and coined...

>So what do we call Arctometatarsalia + Maniraptora
>exclusive of all other theropods? 

Maniraptoriformes Holtz 1996.

>       Also, it seems to me that these things represent one of or the
>most important radiations of dinosaurs in their history, and what with the
>acquisition of many top-predator roles, small carnivore roles, small and
>large herbivore roles, the maniraptora+arctometatarsalia were set up such
>that it was possible that eventually they could even have become major
>contenders in, if not dominant in, the herbivore role as well as the
>carnivore role.

Damn straight!!

>Who knows what they would have done if not for that big
>rock (maybe. possibly. It's concievable. Who knows? I don't want
>to start *this* argument again!).

Hey, even with the big rock, maniraptoriform theropods still outnumber
mammal species 2:1...
  
>       Also, how is "Aves" defined, anyways? Stem based, character based,
>node based?

Ah, now this was (and remains) a sticky subject:

Gauthier defined "Aves" as a node-based taxon, the most exclusive clade
comprised of tinamous, ratites, and neognaths, and all descendants of their
common ancestor.  Archaeopteryx, Ichthyornis, Hesperornis, etc., are thus
outside of Aves, and were given a new taxon (Avialae, the Bird Wings) to
contain them.  [Note that most ornithologists have used the name
"Neornithes" for the same clade Gauthier labels "Aves"].

However, as Luis Chiappe and others have pointed out, "Aves" has a much
broader usage than any other dinosaur taxon names, since "aves" is still the
common word for "birds" in most romance languages!  Therefore, he has
proposed to leave Aves as a more inclusive taxon (a node-based taxon,
Archaeopteryx + modern birds and all descendants of their common ancestor),
and use Neornithes for the node-based taxon joining all the extant lineages.

Several of us are at work clarifying other phylogenetic taxonomic
definitions within the Archosauria.

Hope this helps,

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