Re: Placement of Segnosauria (was Re: Details on Nanshiungosaurus bohlini)

["Mickey_Mortimer" <Mickey_Mortimer@email.msn.com>]

George Olshevsky wrote-

> I think Tracy meant to say that the dentary is too >big< for the theropod
> suggested by the size of the postcrania. This effect is additionally
> exaggerated because in segnosaurians and in oviraptorosaurians (also in
> ornithomimosaurians) skull length is fairly small relative to femur
length,
> when both measurements are reliably known for a taxon.

Well, in Erlikosaurus the dentary is 68% of lower jaw length, so the lower
jaw of Beipiaosaurus would be 95% of the femur in length.  Using the ratio
of alveolar length to lower jaw length on Alxasaurus gives a mandibular
length of 397 mm, or 79% of femoral length.  No skull material has been
found with hindlimb material in therizinosaurids.  Of course, Caudipteryx
and oviraptorids have very short skulls, so their ratios are much smaller
(52-53 in Caudipteryx and 50-70 percent or so in oviraptorids).
Microvenator likewise appears to have a short skull.  However, caenagnathids
and the Australian basal oviraptorosaur both appear to have normal, elongate
skulls that would probably be close to the femur in length.  Unfortunately,
mandibular remains have not been associated with hindlimb elements in known
caenagnathid specimens and the hindlimb of the Australian species is
unknown.  Examination of the ratio in other outgroups is hindered by a lack
of consensus, but segnosaur-oviraptorosaurs are often seen to be the sister
group of eumaniraptorans (as they are in my analysis).  Some
eumaniraptorans, such as Velociraptor, have skulls that exceed the femur in
length.  Also, some basal coelurosaurs, like compsognathids, have skull
equaling or exceeding the femur in length.  Because of this, I don't feel
the dentary preserved with Beipiaosaurus is too large too be part of the
holotype.

Mickey Mortimer