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Re: Thero palms, Prehistoric Times, and grants



At 11:47 AM 3/19/99 -0800, Ralph W. Miller III wrote:

>I didn't attend the Ostrom Symposium, and I am wondering where the
>compsognathids nest in the latest cladograms.

In my cladogram, compsongathids bopped around (under different runs) as
outside of Maniraptoriformes, as basal maniraptorans, or as basal
arctometatarsalians.

Definition-wise: Maniraptoriformes = all descendants of most recent common
ancestor of _Ornithomimus_ and modern birds; Maniraptora = all taxa sharing
a more recent common ancestor with modern birds than with _Ornithomimus_;
and Arctometatarsalia = all taxa sharing a more recent common ancestor with
_Ornithomimus_ than with modern birds.

>I would also like to know if
>there is at present a consensus regarding the anatomy of the compsognathid
>wrist.

The carpus of compsognathids is finally better understood, via Currie's work
on all known _Sinosauropteryx_ specimens.

>The Holtz cladograms place _Compsognathus_ outside of the Maniraptora
>(as then defined) in the 1994 analysis, and outside of the Maniraptoriformes in
>the 1996 analysis, meaning that this genus did not exhibit the
"maniraptoriform"
>forelimb and manus anatomy.  By contrast, Gauthier's analysis considers
>_Compsognathus_ to possess these characters, placing it within the taxon,
>Maniraptora, as it was defined at the time (1986).

Please note: at those times (and even at present) the wrist of
_Compsognathus_ proper is not well preserved!!  Only through _Sino._ do we
have a good idea of its structure.  The variable position of compsognathids
in earlier studies reflects the nature of compsognathids in general: they
are not particularly specialized, and share only few derived features with
any particular advanced clade.

(Gauthier placed _Compsognathus_ and _Sinosauropteryx_ and Allosauria as
three parts of a four-way split with Coelurosauria on the cladogram
presented at the Chinese feathered dino exhibit at Yale Peabody).

>(The article explains that
>the most recent of these cladograms, Holtz, 1996, redefined Maniraptora as a
>more exclusive group, comprised of only Dromaeosauridae and Avialae in the
>cladogram at the bottom of page 412).

It should explain that I corrected my invalid redefinition in 1994.  The
proper definition for Maniraptora is the one listed above.

>On the other hand, Thomas Holtz' quote above (March 1999) uses the taxon
>"Maniraptora" to define a much larger group.  Has the definition changed again,
>or is the last word in parentheses in Holtz' post above supposed to be
>"Maniraptoriforme"?

[head banging against the wall...]

No.

See definitions listed at top of posting.

These are the definitions: whether they include a particular taxon or not is
a result obtained by analysis; future analyses may or may not support a
particular suite of taxa within each of these definitions.

>Regarding the diagnosis of _Compsognathus_, I am sure that some of this
>disagreement derives from the disarticulated nature of the carpal and manual
>elements of the _Compsognathus_ specimens, and the fact that some of these
bones
>are missing altogether.

Yes.

>Following the discovery of the well-preserved
>_Sinosauropteryx_ specimens (four specimens in all, the last I heard), the
>wrists and hands of compsognathids should be easier to assess.

Yes.

>The "Theropoda"
>article, written by Philip J. Currie, which is also in _The Encyclopedia of
>Dinosaurs_, includes the following passage on page 733:
>
>"(MANIRAPTORA) has been redefined by Holtz (1996) to include only all theropods
>closer to birds than to ornithomimids.

Actually, it was defined as such by Gauthier, and my 1996 paper was to fix
my previous incorrect 'redefinition'.

>He went on to establish the taxon
>Maniraptoriformes, defined as the most recent common ancestor of _Ornithomimus_
>and birds and all descendants of that common ancestor (Fig. 2).
>Maniraptoriformes are characterized by a pulley-like wrist joint that allowed
>the hand to be pulled back against the body.  This characteristic was
>secondarily reduced or lost in ornithomimids and tyrannosaurids.  Recently
>discovered compsognathids (see FEATHERED DINOSAURS) have well-preserved hands
>that suggest that this character was more widespread among coelurosaurs."

However, the above feature is diagnosis for Maniraptoriformes if and only if
some arctometatarsalians possess this feature.  As more recent analyses
support a maniraptoran (rather than arctometatarsalian) position for
Troodontidae, the expanded semilunate carpal block seems to be a
maniraptoran rather than maniraptoriform feature.

(Tyrannosaurids do, however, have a semilunate carpal block: however, it is
only a small one, as in carnosaurs, _Afrovenator_, etc.).

>Does the compsognathid condition then qualify as Maniraptoran,
Maniraptoriforme,
>or is the carpal condition not advanced enough to warrant inclusion into either
>of these taxa?

>From what I've seen (1/2 of the _Sino._ specimens), it is similar to the
condition in tyrannosaurids and carnosaurs and _Scipionyx_, not like the
enlarged version in oviraptorosaurs, troodontids, dromaeosaurids, birds, etc.

Hope this helps.
>

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661