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Re: Kinetic skulls



Waylon Rowley wrote-

> I believe I once read that Coelophysoids have such a
> weak maxillary-premaxillary articulation that it
> allowed for some degree of movement, whereas in the
> Spinosauridae an extended plate-shaped anteromedial
> process unites them firmly. Technically then, couldn't
> this be a different form of prokinesis, or is there
> another term for it?

As far as I can tell, prokinesis refers to having a dorsoventral flexion
joint anterior to the orbit, so I suppose the subnarial joint of
coelophysoids would count, although it is certainly a different type of
prokinesis than that seen in alvarezsaurids or ornithurines.  Actually,
closer examination of the literature reveals that the prokinesis of Shuvuuia
was also different in detail from ornithurines.  This is based on the
ventral flexion zone being caudal (not cranial) to the lacrimal and the
dorsal flexion zone being between the frontals and prefrontals (not
nasal-premaxillae).  Tyrannosaurus has been shown to be akinetic (Molnar,
1991).  Ornithurine-type prokinesis depends on the lack of postorbital-jugal
and quadratojugal-squamosal contact, which is a combination not found in
most theropods.  Avimimus may be an exception, but its skull is fused,
preventing any kinesis.  Some amount of kinesis has been suggested for some
theropods (eg. Carnotaurus, Allosaurus), but this was certainly not
homologous to the condition in ornithurines.

> Which reminds me; the Spinosauria
> also have secondary palates, though due to lateral
> compression of the skull. BTW, I don't think all
> coelurosaurs have well developed secondary palates
> because my reconstruction of the Deinonychus skull
> shows 2 very large anterior palatal vacuities (which I
> think Ruben misinterpreted as choanae and used them as
> evidence for a varanid-like respiratory tract in
> Dromaeosaurids?). Get back to me on this....I'd like
> to know if secondary palates could be phylogenetically
> useful characteristics.

I forgot about spinosaurids in my brief response.  My coelurosaur
information comes from Holtz (2000) in his GAIA paper (pg. 27).  His matrix
shows the following distribution-
0- Coelophysidae, Dilophosaurus, Ceratosaurus, Abelisaurus, Carnotaurus,
Megalosaurus, Torvosaurus, Megalosaurus? hesperis, Afrovenator,
Eustreptospondylus, Piatnitzkysaurus, Monolophosaurus, Sinraptor,
Carcharodontosaurus, Giganotosaurus, Neovenator, Allosaurus, Dryptosaurus,
Compsognathidae, Ornitholestes, Proceratosaurus, Archaeopteryx
1- Spinosauridae, Tyrannosauridae, Ornithomimidae, Segnosauria,
Caenagnathidae, Oviraptoridae, Alvarezsauridae, Troodontidae,
Dromaeosauridae, Ornithothoraces
So, I probably should have said most maniraptoriformes have secondary
palates.
I know what you mean regarding Deinonychus, the reconstruction of Ostrom
(1976) doesn't seem to have an extensive palatal shelf.  However, the
description states-
"The most priminent feature visible is a medially directed shelf or ledge,
some 15 to 20 mm above the internal alveolar margin, that appears to extend
the entire length of the maxilla.  Anteriorly it is a thin plate of bone
with a rather sharp medial edge, but posteriorly it forms a rounded ridge.
This appears to have been nearly horizontal and probably represents the
lateral portions of a secondary palate the remainder of which was
cartilaginous or membranous."
Regarding Velociraptor, Barsbold and Osmolska (1999) state-
"The left palatal shalf of the maxilla is partially preserved in ZPAL
MgD-I/97, its rostral portion lacking.  It is moderately wide rostrally (at
least 7 mm), and has a smooth, upturned medial border.  As preserved, a part
of this border contacts the vomer along the region rostral to pila
interfenestralis.  The shelf is inclined dorsomedially-ventrolaterally.
This inclination gradually decreases rostrally, and the shelf was probably
almost horizontal at the contact with the premaxilla.  Caudally, the palatal
shelf underlies the medial surface of the jugal, close to the contact of the
latter with the lacrimal shaft.  Rostral to the lacrimal, the medial border
of the palatal shelf is in contact with the palatine."
Regarding Achillobator, Perle et al. (1999) write-
"The palatal shelf is well defined reaching anteriorly almost to the
premaxilla-maxillary contact"
Dromaeosaurus can also be seen to have a maxillary palatal shelf (Currie,
1995, fig. 1).  Here, the problem with Ostrom's reconstruction can be
clearly seen, as it has much too wide a snout.  This makes the maxillary
palatal processes seem less extensive than they should be, although they
still look a bit smaller than in Dromaeosaurus.  Despite this partial
explanation though, I still have to agree with you.  Even Dromaeosaurus
doesn't have much of a palatal shelf compared to ornithomimids, segnosaurs
and oviraptorids.  In fact, it looks smaller than that of Allosaurus
(Madsen, 1976).  Are one or more reconstructions erroneous?  Is the
character difficult to see in two dimensional figures?  I'm not sure, so I
can't answer your question.  Perhaps Tom will enlighten us, as he seems to
have experience in identifying it.

Mickey Mortimer