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Theropod taxonomy, Oddus endi, et al. [ponderous]
All ">" are Nick Pharris, I combined some posts, :
>Hi, guys! I was just reading through recent dinosaur digests to get
>back into the swing of the list when I noticed a post from John
>R. Wagner wondering where I've been. Made me all misty-eyed to
>realize you care ;-).
Maybe, or maybe we just needed to fill some disk space with
dinosaur digests! :)
> Metatarsal V is depicted as platelike. This is less advanced than in
>dromaeosaurs and _Archaeopteryx_.
Think synapomorphies! What other taxa have this?
>The apparent triangular obturator process in _Alxasaurus_ (provided
>the ischia have been correctly identified) would make therizinosaurs
>coelurosaurs, rather than carnosaurs.
Yeah. I have a weird, nagging feeling that there is an
important bit of the Theropoda that we are missing that would
straighten this out. I realize that this is usually the case, and
that we are very unlikely to ever find an intermediate, but I think
this is gonna be one of those problems that will be solved by new taxa
and not new cladograms.
>My guess is that therizinosaurs are descendents of early,
>ornitholestian-like coelurosaurs. In fact, a few characters (small
>head, femur longer than tibia, decurved dentary) may support a
>direct link between _Ornitholestes_ and therizinosaurs. But I'm not
Although I've been known to use some of these characters
myself, none of them are diffinitive. On behalf of your theory, I
will say that Ornitholestian skulls look a *LOT* like Erlikosaurus'
>While that may be true, I feel I should point out that mtt I
>apparently does not participate in the ankle joint. According to
>the description of _Alxasaurus_ by Russell and Dong, the proximal
>end of mtt I in _Erlikosaurus_ (sorry, Tom, it just looks better to
>me that way) and _Therizinosaurus_ is deeply cupped to recieve the
>side of the shaft of mtt II. Digit I points away from the other
>digits, as in all other theropods, rather than lying parallel to
>them, as in prosauropods.
I noted recently on the list that mtI of Erlikosaurus is
short, small, and just *looks* like it could be secondarily elongated
(see my post on evolutionary reversals in important funcitonal groups,
of, I believe, last Thursday (5/30) or so...).
>P.S. It's good to hear that there's a new reconstruction of the skull
>of _Erlikosaurus_. The old reconstruction of the cheek region was
Postorbital-parietal contact, perhaps? Or shall we check
under the hood for the rather odd looking palate? then there's the
wacky nasal/lacrimal/max structure (as reconstructed, it is vaguely
reminiscent of the the new (undescribed) troodontid from Mongolia
figured in the Scientific American article of 1994 and Mark Norell
et. al. book on the American Museum).
>Interesting! Is it possible, then, that _Monolophosaurus_ and
>_Piatnitzkysaurus_, say, are true megalosaurids, considering the
>_Megalosaurus_-like premaxillary ramus of the maxilla of
Piatnitzkysaurus? The Fossils Say YES! (but they say it softly)
Monolophosaurus? Anyone's guess. I think Sereno's dataset may be
a little off.
>A couple days ago, Tom Holtz referred to a "'mononykine'
>alvarezsaurid." I'm pretty suspicious that Mononykus probably isn't
>an alvarezsaurid at all, having pored over Bonaparte's description of
>_Alvarezsaurus_ (thanks again, Tracy!).
>The foot of this animal is highly distinctive.
>Some of these features are also found in troodonts, but metatarsal III
>is only slightly pinched, the glenoid socket faces backward and down,
>and the pubic peduncle extends ventrally farther than the ischiadic
>peduncle, all indicating that _Alvarezsaurus_ is closer to
>dromaeosaurs than to troodonts.
> I would put it in a clade Dromaeosauria along with _Itemirus_ and the
There seems to be a lot of this going aroung. To be perfectly
honest, it looks to me like some specialization of pedal digit II may
be primitive for the Coelurosauria. This would hold well with the
Paul theory of secondary flightlessness (Dinogeorge, you get credit
too...). In any case, since we have yet to identify the metatarsus
and pes of a truly basal troodont, I do not think that the sort of
determination you are trying to make can be done.
! Jonathan R. Wagner ! "Camin-Sokal Pars- !
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