Re: Sclerotics and nose bending (fwd)

["Jaime A. Headden" <qilongia@yahoo.com>]

  On avian kinetism:

  Since Matt's not answering (away, silent, hmmm...),
a simple address of avian cranial kinesis with
perspective of dinosaur cranial kinesis might be in
order.

  There are a variety of cranial joints in a birds
skull, being

prokinetic = joint between nasal and frontal, loss of
connection between lower jugal bar and inter-fenestral
struts, allows snout to move up or down.

mesokinetic = joint between frontal and parietal,
basal reptilian condition.

  prokinesis works in two ways: rhynchokinetic skulls
do not bend at a joint, but rather before it, on a
thin strut of the nasal above the external
naris/antorbital; ratite rhynchokinesis operates by
reducing the lachrymal bar, so that it does not
contact the jugal bar; and charadriiform
rhynchokinesis operates with a fixe lanchrymal bar by
bending at the lachrymofrontal juncture, similarly
reduced as the narial bar to form an area of bending,
and producing the characteristic schizorhinal nostril,
as opposed to the holorhinal (as in all other birds
except ratites). The second way is the streptostylic
quadrate, where the bone hinges on the braincase, and
allows the jugal bar to swing forward.

  I'm using Bock (1964) for my major source on birds,
and Versluys (1962) for lizards (specifically,
*Varanus*)

  Dinosaurs (non-avialaean, of course) had only the
mesokinetic skull, but additionally loose connections
(as discussed for *Coelophysis* but also remarked on
for *Ceratosaurus* and *Allosaurus* [see works by Paul
and Bakker for this effect]). Similarly, Barsbold
(1977) found that *Oviraptor* possessed a few other
hinges, but very moderate ones, also found in snakes,
such as a premaxillary-nasal hinge; the dentary could
orient against the rear-half of the jaw, etc. Horner
or Weishampel (dates??!!) described movement in
hadrosaur jaws that gave them extremely effective
dental batteries and eating capabilities. Thus, while
dinosaurian kinesis is not remarkably evident as in
birds, it is remarkable nonetheless.

  Ontogenetically, it is observable that younger
oviraptorosaurs have as loose cranial connections as
adults, as seen from Osmolska (1976) through Webster
(1996), with various papers by Barsbold (1976, 1977,
1979a,b, 1981, 1983, 1985, 1986, 1990, 1997a,b) in
between. Cranial kinesis in ankylosaurs is probably
moot, though, given all the armor, and in ceratopians,
it might actually be a hinderance in the efficiency of
the slicing apparatus there, but in ornithopods, it
must only be advantageous given the often fragile
connections between bones (see Weishampel et al., 1990
for various ornithopod groups, and check the high
number of dissarticulate skulls, as well as other
papers by Horner for *Maiasaura* and Weishampel for
european iguanodontians.

  Evolution of avian kinetism has been remarkably
quiet, as Bock (1964) describes, and a simple
"thecondontian" origin from mesokinetism is favored at
that point.

  Because this ain't my particular field, I should
shut up [now]. :)

===
Jaime A. Headden

"May I lure us, ere the mote ends us?"

Qilong, the we---is temporarily out of service.
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