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Re: Re: Removing segnosaurs from ...



>Adding to the list of characteristics shared by prosauropods and
>segnosaurs, trait number 19, interdental plates.
>
>1) A relatively large premaxillary (compaired to theropods).
>2) Elongate vomers.

Also typical of theropods.

>3) Elongate nares.
>4) Deep narial shelf.
>5) Deeply recessed anteorbital fossa and fenestra.

Actually, this is a VERY theropod (or at least avetheropodan) character.

>6) Downwardly deflected dentary.

Also in ornithomimids.

>7) General tooth structure.

Same tooth structure in troodontids, and similar to those of toothed
ornithomimosaurs.

>8) Broad tetradactyl pes (which George Olshevsky quite convincingly 
>    shows is not a "reversion").

If you wish to be a strict Dollist (Dolloist?  sp.), sure.  If not, you can
recognize that homeobox genes show that there really aren't any significant
morphological characters that can't be reversed.

>9) "T" -shaped postorbital.
>10) "S" -shaped quadrate.
>11) Low occiput.
>12) Prearticular running the whole lower and forward margin of the     
>    external mandibular fenestra.
>14) The Prearticular-Angular-Splenial complex.
>15) General hand structure and articulation.

Actually, if you see the original Russian literature (esp. papers by
Barsbold and Perle), you will see that the therizinosauroid hand is VERY
avetheropodan.

>16) Depressed jaw joint and a small "coronoid" process.

See also in ornithomimids and oviraptorids

>17) Lack of the maniraptoran "pulley-action" elbow-wrist complex 
>   (i.e. the arms don't fold like birds').

Actually, as per the Russian lit listed above, the hands of
therizinosauroids DO have a very nice semilunate carpal pulley structure,
and probably could fold their hands inward.

>18) Lack of the Avetheropodan "double-jointed" lower jaw.
>19) Interdental Plates.

Now, you really cannot use interdental plates as uniting therizinosauroids &
prosauropods, as they are also very typical of theropods.  At worst, they
are primitive for Saurischia.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084