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Re: Re: Removing segnosaurs from ...



><<>1) A relatively large premaxillary (compaired to theropods).
>>2) Elongate vomers.
>
>Also typical of theropods.>>
>
>The theropods that you are claiming that segnosaurs evolved from however, all
>have tiny vomers.  You can't tell me that the oviraptors that you claim have
>a sister relationship with the segnosaurs don't have some of the smallest
>vomers ever encountered.  And, quite obviously, segnosaur premaxillaries are
>gigantic, while theropods' are small.

Uhmm, have you looked at the vomers of a dromaeosaurid lately?  Or an
ornithomimid?  Or a troodontid?  Or a tyrannosaurid?  Now, say again that
the theropods cloest to the therizinosauroids have tiny vomers... The
autapomorphies of a sister taxon (such as Oviraptorosauria) have no bearing
on the character state of the more inclusive taxon.

><<>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.>>
>
>Funny, this is from the list of characters that Barsbold and Osmolska put in
>"The Dinosauria" linking prosauropods with segnosaurs.

Yeah, funny that.  Check out the skulls of Allosauridae, Tyrannosauridae,
Ornithomimimidae, Troodontidae (correctly prepared, that is),
Dromaeosauridae, and (especially) Oviraptoridae some times.  You will find
that they all have deeply recessed antorbital fossae.  (How a fenestra gets
any more recessed than it is by definition, I don't know ;-) )

> I would very much
>like you to find me a theropod that has as large nares as _Erlikosaurus_.

How about Monolophosaurus?  Now, I don't think that there is any close
relation between the two, but it does have a whopping huge naris.  Also, a
point needed to be made is that we, at present, do not know which cranial
characters of Erlicosaurus are unique to that genus, and which apply to the
Therizinosauroidea as a whole.  The skull of Alxasaurus is very fragmentary,
and none of the other taxa have good cranial material.
>
><<>7) General tooth structure.
>
>Same tooth structure in troodontids, and similar to those of toothed
>ornithomimosaurs.>>
>
>Are you saying that Troodonts have no teeth in the fronts of their jaws?

Absence of teeth in the premax is NOT "general tooth structure"!  However,
since you brought it up, ornithomimids and (of course) oviraptorids lack
teeth in the premaxilla.

> You
>yourself agree that segnosaurs are herbivorous, how can you claim that their
>teeth are identical to Troodonts?

Yes, how COULD I say that?!  If you have access to last year's abstracts
from the SVP meeting, take a look at an abstract by Holtz, Brinkman, and
Chandler.

>
><<>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.>>
>
>I have a photograph in my hands of the type specimen of _Alxasaurus'_ wrist.
> For two and a half weeks I have not been able to find the "semi-lunate"
>carpal from the photograph just as I could not see it when I saw it in person
>in Vancouver.  Would you please be so kind as to tell me where it is?  As far
>as I am concerned, it is not there.

Did you take the photo from the mounted skeleton?  Much of that is (how to
put this politely) conjecture.  In the actual material, it is quite
present.  Further, those other therizinosaurs for which the carpus is known
(Therizinosaurus and at least one of the small ones [I think Segnosaurus
itself]), clearly show the pulley structure, and in fact were used by
Barsbold in his 1976 monograph to describe that very structure.
>
>I cannot see any characters linking theropods to segnosaurs.  The semi-lunate
>carpal block is not there, the tetradactyl pes is identicle to prosauropods,
>and the head and jaws show no great affinities to theropods.

Wrong: the semilunate carpal block is present, and the head and jaws show
abundant synapomorphies with several maniraptoriform theropod groups (in
particular, Bullatosauria and Oviraptorosauria).

You did not discuss above the inflated parasphenoid capsule or the enlarged
endocranial cavity.  How do you reconcile these with a prosauropod origin of
Therizinosauroidea?

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