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:
While I suppose some of the blocks could
have come from different specimens, a large portion of the elements are in the
main block. These include a manus, dorsal vertebrae, ilium, pubis and
hindlimb. These have theropod characters (dorsal pleurocoels, semilunate
carpal, three metacarpals, proximal ends of metacarpals I and II closely
appresed, metacarpal III bowed, combined lengths of manual phalanges III-1 and
III-2 equal to III-3, narrow pubic apron, wing-like lesser trochantor,
metatarsal I reduced, metatarsals III and IV compressed proximally, etc.), but
also segnosaurian synapomorphies (deep preacetabular process (contra Xu et
al.), astragalus only partially covers distal end of tibia, metatarsus reduced
in length). It is most parsimonious to conclude that Beipiaosaurus is a
basal segnosaur and accept the other blocks that contain segnosaur or
theropod-like elements as belonging to the specimen.
While there may not be many elements
preserved in the pes of Beipiaosaurus, the bones that are there are
well-preserved, if sometimes partially covered by the tarsus. Metatarsal
I is obviously flattened and tapered proximally, as
in theropods.
-
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)
Yes, the Lufeng dentary along with the
dentaries of Beipiaosaurus, Alxasaurus, Erlikosaurus and Segnosaurus all have
lateral shelves. This would be a convergence between segnosaurs,
ornithischians and probably prosauropods. The Lufeng specimen may
actually come from a prosauropod, although this is currently
debated.
Timothy Williams already sited the
studies that find Massospondylus did not have a beak, as proven by a few new
skulls that are better preserved.
-
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?
This has never been done, so you may have
a valid point. I tell you what, you provide me with a list of
synapomorphies you think both prosauropods and segnosaurs share,
and theropod synapomorphies segnosaurs lack (I'll check Paul 1984 as
well) and I'll add prosauropods to my phylogenetic analysis of
coelurosaurs. My analysis contains over 300 characters (including those
used by previous analyses) and forty-odd taxa, so it should be fairly reliable
as far as phylogenetic analyses go. Of course, I'll also add some basic
theropod synapomorphies that aren't there currently because all of my taxa
exhibit them.
Hey, this reminds me of an analysis I
agreed to do at the beginning of the year regarding secondary
flightlessness. I agreed to delete all flight-related characters from my
analysis to see if avians only clustered together because they are
volant. I think it was in response to John Jackson. In any case,
I've now performed that analysis and I can post the results if enough people
are interested.
Their skulls look different at first
glance, but most postcranial elements are fairly similar and the palates share
some odd synapomorphies. In any case, as Tim said "evolution
happens".
Besides, what's behind the mysterious
Desertiana? I only know the term was coined by L. A.
Nesov.
According to Olshevsky's post on the list
back in 1996, the genus is a plant. It is a new generic name for
Celliforma favosites. I'm not sure how his later statement that
Deseriana is a form-taxon of segnosaur fits into this, perhaps it is a
typo. George will probably have something to say regarding this
matter.
Mickey
Mortimer