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Re: Re: Alxasaurus and segnosaurs



>Exactly the questions I had. The measurements given in Russell & Dong seem
>accurate and conform to what I've seen of the type specimen, but the figures
>don't seem to match the measurements. And the mounted skeleton of _The
>Greatest Show Unearthed_ definitely is at variance with the postcranial bones
>exhibited alongside(!).

On this last bit we both concur!!
>
>Segnosaurs started out as theropods, but when skull material started being
>described, they were quickly moved over somewhere into the
>sauropod-prosauropod clade, "sedis mutabilis." The recent description by
>Clark et al. of the skull of _Erlikosaurus_ would have moved them back to
>Theropoda even without _Alxasaurus_, but I think they stacked lots of very
>minor, easily reversed and unreversed skull features against a few really
>robust postcranial characters, thereby numerically winning the synapomorphy
>battle but losing the phyletic war.

In your dreams... (but, of course, you may yet be proven correct).
>
>>Boy, what a mess!
>>Please, can someone clear this up once and for all?
>
>Not likely. I certainly wouldn't budge until someone showed me how to derive
>a prosauropod-like foot from a tetanuran theropod foot and a prosauropod-like
>dentary with prosauropod-like teeth from a tetanuran theropod dentary.

A)  You shorten the lower half of the tetanurine foot, and you get a
prosauropod-like one.  A short foot is not inconsistant with a fat,
slowmoving herbivore (with Freddy Krueger claws for protection, at least in
Therizinosaurus).

B) "Prosauropod-like teeth" show up in basal ornithomimosaurs, troodontids,
(and I expect in ancestral oviraptorosaurs).  The dentary of Harpymimus is
not greatly removed from that of therizinosaurs.  It would be consistant
with a lineage of theropod evolving exclusive herbivory.

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