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Re: AVIMIMUS PREMAX.



Peter Buchholz wrote:

<<Other parts of the anatomy, such as the premaxilary with
crenulations . . . ,>>

Darren Naish wrote, in reply to Pete:

<Once again I will mention the possibility that the _Avimimus_ premax
does not go with the cranium of the genus, but may instead be from a
hadrosaur.>

  The preservation of the fragment of *Avimimus'* beak (if that's who
it belongs to) is such that the premaxilla is appressed (is this the
right word?) into a vertical bar lacking any indication of an external
naris. This meant the naris (if present, you never know) would have
been more dorsally and caudally placed, as in oviraptorosaurs, and
unlike birds, hadrosaurs, or baby hadrosaurs. Both *Hypacrosaurus* and
*Maiasaura* hatchlings have anteriorly-placed external nares, that
clearly abut the premaxilla's dorsal process, and though they possess
a nasal fossa, the fossa on the beak fragment possesses a separat
foramen, like the antorbital foramen.

  To throw a monkey-wrentch into my works, ceratopsians like
*Triceratops* have nasal fossae with holes. Darren Tanke, or any other
ceratopsian worker, do you know if any juvenile or sub-adult
ceratopsians have these? It is _not_ a protoceratopsid's or similar
form's premaxilla--maxilla fragment.

<This may or may not be correct. But Pete's contention that a
crennulated premax would be suggestive of oviraptorosaurian affinities
are a little suspect aren't they? A vaguelly crennulated premax has
been figured for _Oviraptor mongoliensis_, but I'm not 
convinced these represent proper crennulations (which should be
denticulate). And are they present in other oviraptorosaurs? Not as
far as I'm aware.>

  Crennulations are known in every oviraptorosaur premaxilla I've seen
(except for the type of *Oviraptor* where this bone is missing).
Whether these form denticulations or not comes a little stronger in
the defense of *Avimimus* because *Conchoraptor* has them, true
denticulations, one on each side of the pointy beak.

  The rest have real crennulations, and even GI 100/42, biggest of all
described oviraptor skulls, has what may be denticulations, for they
are evenly spaced and sized along the premaxilla's ventral edges. Both
*Ingenia* and "Rinchenia" have strongly pointed premaxillae, longer
and lower in the front and rising above the maxilla's ventral margin,
unlike other oviraptorosaurs. These premaxillae are jagged-edged, like
a toucan's serrated beak.

  A noteworthy genus is *Caudipteryx* (yeah, everyone's capitalizing
on this fellow) who also has denticulate [?] serations behind the
teeth, on the caudal half of the premaxilla.

==
Jaime A. Headden

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

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