[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Feeding Adaptations of Incisivosaurus gauthieri



Well, thanks to Mickey I have this tonight.

  A cursory glance through the paper permits a consideration of the
evolution of this animal, which I must compare somewhat favorably to some
anomodonts. That is, especially, *Suminia getmanovi*. This taxon (the
oviraptorosaur) has a skull that is superficially like the BMP 0001
specimen of *Caudipteryx*, only deeper in the snout, and more
plesiomorphic. There is a maxillary fenestra, a subcircular orbit, and
narrow adductor chamber, and a very long vomer, about 55% skull length.
The teeth are very unique, and at first I was shocked to see references to
the "bunny" like comparisons, but that is an accurate assessment. The
first to premaxillary crowns are side by side and the space between them
marginal, relatively less than that seen in the other teeth versus
mesiodistal length of the crown. They are transversely compressed and
incisiform in nature, and slightly procumbent.

  The other premaxillary teeth, unlike the dentary and maxillary crowns,
are more subconical and carinate, but unserrated, and recurved. Strangely,
one premaxilla has four crowns (the right) and the other has five.
Maxillary crowns are labiolingually compressed and chisel-shaped, a form
not seen in other dinosaurs except some superficial features of some
sauropod crowns. I suspect the roots of these teeth are very long, as the
tooth bearing bones possess distinct subdental platforms relative to crown
heights. Dentary crowns are few in number, and as in the dental groove of
the caenagnathids, distinct in their position. There are no interdental
plates, and the symphysis is edentulous. A tiny coronoid is present above
the rostral end of the splenial. Like oviraptorids, the pterygoid/palatine
contact is below the jugal and exposed laterally, and the ectopterygoid is
biramal with a small palatine fenestra (in oviraptorids this is a
foramen), and there is a small, laterally-oriented trochlear pterygoid
flange. The articular surface is a cotylar glenoid and socket-shaped in
form, but elongate, so that a fore-aft mandibular action was present.

  Needless to say, this taxon satisfies a few predictions of my own (which
some on this list have been privvy too and should be better elaborated on
soon. Press descriptions regarded the teeth as grinding in nature ...
rather, they are shearing, with low angle wear facets, though the rostral
crowns were not used in such a manner; likely, the incisiform first two
teeth interacted with a dentary rhamphotheca, and the premaxillary "beak"
was reduced and not elaborately developed. This suggests that the animal
was a cropping browser, probably on soft plants based on the absence of
enlarged crowns, though do not hold me on that. The premaxillary teeth may
have functioned as sagittal shears, cutting backward, while the
maxillo-dentary sets were vertical shears, and the premaxillary
incisiforms were initial croppers.

  Some evolutionary observations (general):

  the lachrymal resembles *Ornitholestes*, interesting ... the dentary a
more derived sort compared to *Microvenator*, the foramen magnus is very
large, where the occipital condyle is deeply U-shaped. The skull appears
to have been diagenically transversely compressed, resulting in the narrow
rear skull, poartially separated supraoccipitals at the midline, and shape
of the occipital condyle. The vomer is very long, a feature shared with
*Erlikosaurus*, and the ectopterygoid's shape is similar. The internal
choanae are very long and narrow, and the vomer has a distinct rhombois
corpus, set within the caudal half of the secondary palate. The
ectopterygoid, curiously, has a very long lateral process contacting the
medial surface of the jugal, for most of the former bone's length. Both
pterygoids are in contact with each other medially at their rostral ends,
a feature with increases resistance to bending, but I wonder how much of
this may have been affected by compression?

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

__________________________________________________
Do you Yahoo!?
New DSL Internet Access from SBC & Yahoo!
http://sbc.yahoo.com