RE: Oviraptor wrist

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Jaime A. Headden

> All major genera of Maniraptora
> (Oviraptor, Deinonychus, Velociraptor, Chirostenotes,
> Caudipteryx, Archaeopteryx, etc.) have semilunates
> with a distinct halfmoon profile. A similar form of
> the semilunate in maniraptoriform theropods includes
> the compressed discoidal (but separate) bones of the
> ornithomimosaurs, and the cuboid and fused form in
> troodontids and tyrannosaurids (the MOR (Wankle) and
> FMNH (Sue) specimens of *Tyrannosaurus rex*, to be
> exact).

Also, a subadult tyrannosaurid (previously assigned to _Daspletosaurus_ sp.,
but quite possibly _Albertosaurus sarcophagus_) also has a well developed,
albeit small, semilunage carpal block: comparable in relative size and shape
to the condition in (among others) _Coelurus_ and _Scipionyx_.

A bone (or rather, bone complex) of the type described above (the small
version of the SLC (semilunate carpal block), rather than the expanded
version found in maniraptorans) has been identified in _Allosaurus_ and
other carnosaurs.

Several papers at this year's SVP will address the evolution of the SLC.  To
give the version I presented at the Ostrom symposium, the history of the
carpus of theropods runs something like this:
Basal condition (separate distal carpals I & II, pre-theropodan)
 ->Fusion of distal carpals I & II (found in some coelophysoid specimens,
for example)
   ->Development of transverse trochlea and semilunate shape (found in
carnosaurs, basal coelurosaurs such as _Coelurus_ & _Scipionyx_, subadult
tyrannosaurids, etc.)
     ->Modification I: SLC is greatly expanded in size to cap the proximal
ends of metacarpals I & II (Maniraptora, and Troodontidae independantly if
troodontids are arctometatarsalians)
     ->Modification II: loss of semilunate shape and transverse trochlea,
but retention of fusion of distal carpals I & II (ornithomimosaurs)
     ->Modification III: retention of semilunate shape and transverse
trochlea, but loss of fusion of distal carpals I & II (therizinosauroids).

Note that Modification I is further modified (by fusion of the SLC with the
metacarpus to form a carpometacarpus) in birds.

Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796