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Re: lizard jaws

On Tue, 13 Feb 1996, King, Norm wrote:

> We all know about the remarkable spreadable jaws of snakes that allow 
> them to swallow items larger around than themselves.  To what extent can 
> lizards do the same thing?  Of course, insectivorous lizards wouldn't 
> have to at all, nor would the herbivores.  But are there any carnivores, 
> among the varanids perhaps, that can also spread their jaws (and to what 
> extent)?
> Thanks in advance for any replies.

[ Note to Nick:  Thanks -- MR ]

Lizards, like snakes, have kinetic skulls.  In fact, the snake's skull is 
simply an elaboration of the kinetic system Already found in lizards.  
Primitive diapsids, as I'm sure you know, have two openings in the skull 
behind the eye, separated by bridges of bone.  Lizards have made their 
skulls more mobile by losing the lower bridge (the one between the 
infratemporal fenestra and the lower margin of the skull), and snakes, 
when they evolved from lizards, also lost the bar between the two fenestrae.

The quadrate (bone in the skull that articulates with the lower jaw) of a 
snake is therefore only connected to the roof of the mouth at a single 
point, allowing great mobility in the jaw joint.

Varanids do have highly mobile skulls.  Last I heard, varanids were 
considered the lizard group closest to the ancestry of the snakes 
(through animals like _Pachyrhachis_).

Incidentally, this is one way we would know that the tuatara is not just 
another lizard, even if we had never found fossil rhynchocephalians:  
tuataras retain both spars of bone and two complete temporal fenestrae.

Hope this helps!

> *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
> Norman R. King                                       tel:  (812) 464-1794
> Department of Geosciences                            fax:  (812) 464-1960

Nick Pharris
Pacific Lutheran University
Tacoma, WA 98447

"If you can't convince them, confuse them." -- Harry S Truman