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Re: Coelurus a maniraptoran (for how long?)



...so, a little late...

Ken Kinman (kinman@hotmail.com) wrote:

<And with tyrannosaurs jumping around (and who knows what 
troodonts might do next), I'm not sure the maniraptoriform or
maniraptoran boundaries are very useful anyway (except to keep
ornithomimids stationary).>

  They are very useful. However, let me start off with this
statement: in only one analysis published using cladistic
methods, Sereno's in 1999, plus his preliminary support at this
in 1998 (same analysis), tyrannosaurs move outside of a node
defined as the most recent common ancestor of *Ornithomimus* and
Neornithes, which Tom Holtz, 1995b, named Maniraptoriformes.
This node is one of the most stable, defined groups in
Theropoda, among the rest being Avetheropoda, Coelurosauria, and
Maniraptora. In spite of the mobility of some singular taxa
(those whose names begin with "T" as Holtz has repeatedly
pointed out) plus a few who begin with "C", the consistency and
arrangement of Coelurosauria has remained the same for two
decades. None of these analyses changes where Maniraptora
(Neornithes <-- *Ornithommimus*, also very stable) is, just
because *Compsognathus* might or might not be one -- or
*Coelurus*, for that matter. Perhaps it would mean something if
Maniraptora or Maniraptoriformes were ever interpreted in a
Linnaean or "eclectist" sense, but to my perusal of the
systematic literature, this has never been the case.

  Almost clearly from the beginning, in 1969, Dromaeosauridae
and birds have been allied. Gauthier described several groups
that are characterized by an almost avian yet theropod
appearance, what Paul called "Protoaves" or protobirds, and
others as "dinobirds." Gauthier then chose that Ornithomimidae
is the next stable outgroup, even forgetting the transformations
that tyrannosaurids have gone through that cloud their
relationships, or therizinosauroids, who now have very basal
relatives for which to ascribe to one group, instead of another.
Gauthier, Holtz, Sereno, and Padian et al., have qualified the
nomenclature to assist in refering to these groups.

<The ornithomimids are going to get dizzy with all these groups 
leap-frogging back and forth overhead in both directions.>

  The ornithomimids have been stable in Coelurosauria for over
30 years. As farther from birds than dromaeosaurids are, so only
oviraptorids qualified between them in 1986 and later. My
personal conclusion is that compsognathids and tyrannosaurids
are closely related, even if compies represent the plesiomorphic
state that tyrants dinos and are not their closest allies within
the coelurosaur paradigm.

<I was rather taken aback when you said this morning that it
"doesn't matter what other taxa belong in there." It does matter
to a lot of us.>

  You want to reflect what is contained within Coelurosauria, do
this absolutely. You make arrangements based on ancestry, which
is the clearest present method to finding this. Whether or not
we find it. I should argue Tom's case for it, but...

<Is sacrificing stability of content in the name of "stability
of definition" really the best path to a more stable
nomenclature?>

By saying, "I know what a coelurosaur is, but becuase the other
groups keep changing in content, they must not be stable, so its
a good reason to reject their usage," is to say that taxa can
only be inferred as content-bearing, instead of by any other
method. Or perhaps I'm barking up the wrong sauropod leg here.
This does not reflect the plasticity of relationship, or the
ability to define groups aside from plastic arrangement, which
as you note can change wildly. As Tom said, there will always be
a Maniraptoriformes, and a Maniraptora, and a Eumaniraptora.
These are very stable groups. Their contact is actually strongly
constrained -- it is the position of a few groups, 5 taxa each
or so, that may shift in and out of the defined group. However,
the multitude constituency stays the same. This provides
stability.

<Lots of people obviously don't think so,>

  Generality.

<and anchoring down one genus (even Ornithomimus) in the midst
of all these cladistic jumping beans appears to have been rather
premature.>

  Really? Defining groups on well-known, well-described, and
complete material whose position to birds and one another rarely
changes (1. *Compsognathus* (2. *Ornithomimus* (3. *Oviraptor*
(4. *Dromaeosaurus* + Neornithes)))) It was a good idea, in my
opinion, to choose the eponymous taxon in a well-defined group
whose members share so many features in common Sereno put them
all into Ornithomimidae sensu stricto, so they could not
possibly jump around; so that *Ornithomimus* is a very good
candidate for its position. As Holtz wrote (see in 1999): (2.
*Ornithomimus* (3. *Oviraptor* (4. *Dromaeosaurus* +
Neornithes))) is stable without tyrannosaurs, therizinosaurs,
troodontids, and other taxa which are less well known to
clarify. This is usually the problem, not that the taxa
themselves are perfectly clarified. Remember, systematics gets
clarfied, and to say that shifting taxa demonstrates the
instability of the method is erroneous.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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