WHOOPS!: WHEN IS A QUADRATE NOT A QUADRATE?

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

Some of you may be wondering: How can a threshold to a tympanic sinus be 
also a quadrate cotyle?  I said:

>Another interesting bit of evidence for the presence of a 
>double-headed quadrate in _Archaeopteryx_ is the weird flat >threshold 
to the caudal tympanic recess on the London paraoccipital >process; 
Whetstone interpreted it as a quadrate articulation area but >Walker 
suggested otherwise 

I should have said:
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Another interesting bit of evidence for the presense of a double-headed 
quadrate in _Archaeopteryx_ is the weird area interpreted as the 'flat 
threshold to the caudal tympanic recess' by Walker.  Whetstone 
interpreted it as a quadrate cotyle for the medial quadrate head but 
Walker suggested that it was a tympanic recess.  I suggest that the 
interpretation can go either way; what Walker suggested was a pneumatic 
cavity at the base of the paraoccipital process (Fig. 1) may be the 
quadrate cotyle even though it is farther caudal than the prootic 
articulation in Recent birds.  
----------------------------------------------------------

My point, which got maligned when I was editing my original message, is 
that the issue of whether the quadrate of _Archaeopteryx_ was double or 
single-headed is up in the air.  In addition, it can be argued that some 
of the strange features of the paraoccipital process can be quadrate 
cotyles.  As another aside, some of the depressions on the prootic in 
_Archaeopteryx_ may be quadrate cotyles.  

Matt Troutman 
m_troutman@hotmail.com


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