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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
>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
>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.
Dept. of Geology
University of Maryland
College Park, MD 20742