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Re: Therizinosaurs



At 10:17 AM 12/2/97 +0000, Neil Clark wrote:
>I may have missed this.  If it has been on the list previously, 
>please excuse the question.  I have been asked to forward the 
>following question to the list by a colleague.  I have been unable to 
>find an answer myself either......
>
>What is the basis for classifying therozinosaurs as a sister group to 
>the oviraptosaurs?  Is it because of semi lunate carpals or pinched 
>metatarsals or is there more????

You haven't missed anything, because (except for Dong & Russell's paper in
the Sino-Canadian expedition results volume of Canadian Journal of Earth
Sciences (30: 2107-2127)) none of the relevant studies have been published
(Sues' will be out very soon, hopefully; mine will be out next year; don't
know if Novas has his worked out into a paper form yet).

As neither adult therizinosaurs nor oviraptorids have pinched metatarsals
(caenagnathid oviraptorosaurs DO have pinched metatarsi, and Neil would know
more about embryo therizinosaur metatarsals than anyone...), that doesn't
unite them.

The characters in Dong & Russell which were unique to oviraptorosaurs and
therizinosauroids among coelurosaurs:

Basipterygoid processes abbreviated, fused to pterygoids;
Vomers extend posteriorly to basicranium;
Palatine fenestra closed;
Coronoid ossifications absent;
Ulnar facet of humerus expanded, merges with entepicondyle;
Preacetabular ala of ilium greatly expanded vertically;
Postacetabular ala of ilium acuminate.

These are on top of the features placing therizinosauroids among Coelurosauria.

Note that Sereno (1997) considers therizinosauroids the sister taxon to
Ornithomimosauria, and the last time the AMNH crowd presented a cladogram,
they had therizinosauroids as the sister taxon to Bullatosauria within
Arctometatarsalia.

Hope this helps.

P.S.  When is the osteology of the embryo going to come out? (Hint, hint,
beg, beg...)

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