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Re: Theropod Systematics



>Tom Holtz called for a question on theropod systematics so here goes!
>Does the association of a  Caenagnathus jaw with a Chirostenotes skeleton 
>(reported by Hans-Dieter Sues in the 1994 JVP abstracts) 
>prove the synonomy of Caenagnathidae and Elmisauridae? Does the monophyly 
>of the Oviraptorosauria (Oviraptoridae + Caenagnathidae) still stand? If 
>so does this mean that the arctometarsalian condition arose twice in 
>non-avian theropods?
>These questions intrigue me and I hope Tom or someone else can provide 
>some answers.
>

Hmmm, now this is the sort of question I like to see!!

I don't know if Hans is on the net, so I'll start off with what I know.

First off, I haven't seen the specimen in person yet (but I REALLY want to),
but as I recall, it does not actually have a foot or (less certain about
this) a hand.  Elmisaurus and Chirostenotes are based on a foot and a hand,
respectively, and Caenagnathus on jaws.  A previous discovery (of a headless
skeleton) showed that Chirostenotes is an elmisaurid.  The new specimen
shows that Caenagnathus had a skeleton like Chirostenotes.

Here are some of the possibilities:
Dr. Sues' opinion (which I think is probably right on the money):
Caenagnathus jaws belong on the body of Chriostenotes, Caenagnathidae is the
proper name for Elmisauridae, caenagnathids are oviraptorosaurs, and the
arctometatarsalian pes either evolved more than once (caenagnathids and at
least one other time) OR the oviraptorids have secondarily lost the
condition from an ancestor with an arctometatarsalian pes.

An alternative (just playing Devil's Advocate here): the skeleton is
Caenagnathus, and an oviraptorosaur, but is NOT elmisaurid.  The
similarities in the postcrania between oviraptorosaurs and elmisaurids are
primitive for this line of coelurosaurs.  When complete skeletons are found,
those with Caenagnathus jaws have the primitive foot condition, and those
with elmisaurid feet are found to have toothed jaws (Richardoestesia,
perhaps).  Note: there is no evidence of it, but I'll suggest it as a
falsifiable alternative.

Also, I'm now very willing to accept multiple evolution of the
arctometatarsalian condition.  I think, however, it will be exceedingly
difficult to support any cladogram with Tyrannosauridae closer to Allosaurus
than it is to birds.

Later,

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
Colege Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084