CRANIAL KINESIS

["Matthew Troutman" <m_troutman@hotmail.com>]

<<This is not so confined, but infracranial kinesis in squamates is
very VERY derived, and much different from avian and dinosaurian
cranial kinesis.>>

Right and wrong.  Squamate cranial kinesis, which is streptostyly as in 
birds, is somewhat similiar motion-wise to avian kinesis (rostral 
portion of skull moves upward by quadrate action), but is acheived 
somewhat differently. In squamates, the lower temporal arcade is lost 
completely, allowing streptostyly.  This is similiar to the way that 
avians achieve streptostyly in that the ascending and descending 
processes of the jugal and postorbital are lost as well as the acending 
and descending processes of the quadratojugal and squamosal.  

<<Birds, I'll admit, have quite a lot in uncommon, such as a
streptostylic quadrate to allow that bone to move FORWARD (Matt, if
I'm wrong, whack me), as well as nasal/frontal, premaxilla/nasal, and
frontal/parietal hinges, allowing the jaws to move up and down. Check 
out a parrot eating a nut sometime, it's amazing to watch their jaws 
work.>>

The dorsal, articulatory head of the quadrate moves caudad while the 
ventral, mandibular articulation moves rostrad.  The biggest hinge in 
the skull is the nasofrontal hinge.  Oh, and yes, I watched my parrot 
eat a nut today same as it does every day (it could be emphasized that 
parrots are fairly derived birds in terms of prokinesis but I won't 
belabor it).  I suggest you read Bock, 1964 for a discussion of the 
mechanics of avian kinesis and its putative evolution. 

Matt Troutman 
m_troutman@hotmail.com


______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com