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Re: PROTOAVIS, CERATOPID STERNALS



Darren Naish wrote:

<On to something completely different... All mounted
skeletons of _Triceratops_ I've seen have sternal
plates that diverge markedly from one another at their
caudal ends: they are only in contact at the cranial
ends. Have just written a brief critique of Johnson
and Ostrom's (1995) paper in Thomason (the sprawling
_Torosaurus_ paper). Articulated _Triceratops_
sternals were described by Brown (1906) and figured by
him as being in contact for virtually all of their
length (and I see that Tracy refers to this also in
his _How to Draw Dinosaurs_). I therefore took this as
the correct morphology for _Triceratops_: however, I
know from examination of articulated specimens that in
_Protoceratops_ the sternal plates do diverge from one
another caudally, and while checking Chinnery and
Weishampel (1998) I see the same figured for
_Montanoceratops_. Articulated ceratopid material is a
bit hard to come by on this side of the Atlantic..
what is the true sternal morphology for ceratopids?>

  Hmm. If *Triceratops* sternals articulate for most
of their length, and *Protoceratops* --
*Montanaceratops* sternals do not, then ceratop[s]id
sternals make be secondarily articulated along their
length, whereas nonceratop[s]id coronosaurian (don't
know about leptoceratop[s]ids) sternals may have
diverged caudally. The most-length--contact condition
is found in thyreophorans, whereas ornithopodans lack
the conditions (Coombs and Maryanska, 1990; Weishampel
and Norman, 1990; Dodson, 1990, 1995), suggesting that
ceratop[s]ids may have reversed a primitive condition
-- this may be related to size, as even *Avaceratops*
and *Zuniceratops* appear to be rather much larger
than *Protoceratops*, and *Udanoceratops* (and I have
to agree with Sereno, 1999 on this, it appears to be a
leptoceratop[s]id) is secondarily gigantic -- and I'm
not sure, but I don't think sternals are known for
*Udanoceratops*, if I remember Kurzanov (1994?)
correctly.


=====
Jaime "James" A. Headden

"Come the path that leads us to our fortune."

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