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"'Hmmm... if it exists.
Sereno puts it closer to Ornithomimosauria all the time, and there are still
people (like my 0.02 â worth) going around who think segnosaurs are more
probably prosauropods...'"
"Well, the studies of Holtz (1996, 1999,
2000), Frankfurt and Chiappe (1999), Makovicky and Sues (1998), Sues (1997),
Xu et al. (1999) and my own all support an oviraptorosaur-segnosaur
group. Only Sereno (1997, 2000) and Dong and Currie (1994) have
performed analyses that dispute this. Sereno places them as the sister
group to ornithomimosaurs and alvarezsaurids (which I also disagree with),
while Dong and Currie place them as sister group to troodontids, then to
oviraptorosaurs. Other studies, such as those of Britt (using only
vertebral characters) and Elzanowski (using only skull characters), place them
in a group with troodontids, ornithomimids and oviraptorosaurs, but aren't
specific regarding relationships within that group. It has become
increasingly clear that segnosaurs are theropods, with the discovery of
Alxasaurus and especially Beipiaosaurus. I'm fairly certain even George
and Greg agree now."
Sad to say, I don't know most of these
studies, not even their refs. My arguments for putting Segnosauria into
Plateosauria (sensu Sereno: Massospondylus + Plateosaurus)
are:
-
Beipiaosaurus is preserved as jumbled
blocks, each of which contains a few bones. The block containing the coracoids
and furcula could have come from some other animal.
-
The feet of Beipiaosaurus aren't very
well preserved, and it is debatable whether the first metatarsals really don't
contact the ankle (this would be a very unusual reversal as has been discussed
onlist with the problem of sauropod fifth metatarsals).
-
There is this 11 cm long segnosaur dentary from
the Early Jurassic of Lufeng. AFAIK, it shows evidence for cheeks (suggested
for prosauropods, unknown in any theropods): Zhao Xijin & Xu Xing: The oldest
coelurosaurian [sic], Nature 394, 234f. (16 July
1998)
-
A beak at the front of the jaw has been suggested
for e. g. Massospondylus.
-
I think that if one makes up a cladogram and puts
in theropods and segnosaurs, but nothing else, the segnosaurs will more
probably come out next to the theropod clade they have most convergences with
than outside Theropoda. Have there been attempts to include more saurischians
in a cladistic analysis?
-
Oviraptorosaurs and segnosaurs *look* very
different; this might of course change with the discovery of more fossils, but
judging from the present material...
Besides, what's behind the mysterious
Desertiana? I only know the term was coined by L. A.
Nesov.
Am I right that the "Morrison
oviraptorosaur-segnosaur" is the caudal vertebra mentioned in The Dinosauricon
as oviraptorosaurian?
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