Re: Sinosauropteryx ischium

["Mickey_Mortimer11" <Mickey_Mortimer11@email.msn.com>]

Ken Kinman wrote-

>       Thanks to all who responded to the coelurosaur ischium question.  I
> was especially surprised to learn Sinosauropteryx has such a primitive
> ischium.  Maybe Nick Longrich is right that this genus might not even be a
> coelurosaur.  I haven't seen the just published Currie and Chen paper, but
> wonder if it might not at least support a more basal position for
> Sinosauropteryx (more basal than Ornitholestes, for instance).  And will
it
> remain in Family Compsognathidae?

Good questions.  I've divided "Compsognathidae" into three OTU's
(Compsognathus, Sinosauropteryx, Santana compsognathid) for my latest
analysis to see if it remains monophyletic.  Perhaps its members and other
"basal coelurosaurs" will actually have stable positions relative to each
other for once.  I can only hope.
There are some coelurosaurian characters present in Sinosauropteryx-
pneumatic quadrate, only three metacarpals, no supracetabular crest, tall
ascending process, etc.

>       Would a better synapomorphy for Coelurosauria be the "Ascending
> process of astragulus more than 25% tibial length, and loss of transverse
> grooves across condyles"?   Or does that character too possess the
> nebulousness of the ischial characters.

25% is a pretty bad choice for the defining point, as Caudipteryx,
Deinonychus and Velocitaptor have ratios of 22-23%.  As Allosaurus has one
21% of tibial length, I think using astragalar height/width ratios to
diagnose coelurosaurs is a better idea.  The lack of a transverse groove
across the astragalar condyles works, but the groove was not developed until
the Neotheropoda, so Dilophosaurus and more basal taxa will not possess it
either.

Mickey Mortimer