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The Jurassic Jaw



In application of the Lower Lufeng, Lower Jurassic (Lias) jaw ascribed
to the therizinosaurs by Elzanowski (1998) in _Nature_:

  The teeth do not rule out its theropod nature. Possession of a
lateral vertical ridge is also known in troodontids, and I refer
specifically to *Saurornithoides*.

  The distal end the of therizinosaur jaw has a peculiar isoceles
triangle shape, with the dorsal and ventral margins converging
caudally at around a 45 degree angle, and the ventral edge angles
dorsally from the ventral margin of the dentary, while in prosauropods
(and I refer specifically to *Planteosaurus*, the most
"therizinosauroid" like of them all that I can see) it has a narrower
angle, and the ventral margin is largely uninterrupted and the dorsal
marging curves well ventrally to compensate, especially with the
quadrate and mandibular condyles well below the ventral margin of the
maxilla.

  What this jaw may represent is a very basal therizinosaur, possibly
occluding coelurosaurian membership, or a very therizinosaur-like
prosauropod. If so (if either) it would probably be a new dinosaur.
Does the paper go into detail on this?

  It will be a while until I can get access to the paper myself, but
rest assured I will get it.

  Another possibility (to throw more sand in the faces of all you) is
if the therizinosauroids/segnosaurs are an ancient theropod lineage
which by default have prosauropod affinities, but much of the skull
characters seem to refute this.

==
Jaime A. Headden

Qilong, the website, at:
http://members.tripod.com/~Qilong/qilong.html
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All comments and criticisms are welcome!

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