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Re: dino quadrates



GS Paul wrote:

>The identification of an articulation for the quadrate on the London
>braincase is in error. I know this personally and am pretty sure others have
>published that the quad articulated with the squamosal in a theropodian
>manner, but do not have refs on hand

Currie (1985) mentioned Whetstone's positioning of the quadrate cotyle in
_Archaeopteryx_ but did not criticise it.

Currie and Zhao (1993) say:

"The quadrate articulates mostly with the squamosal in troodontids,
although it appears to have also contacted the braincase." (p. 2244)
In this case the exoccipital and opisthonic bones.
This suggests that an articulation of the quadrate incorporating more than
one bone was approached - if not reached - in troodontid theropods.

According to Witmer (1990):

"In other birds considered so far, the squamosal roofs the dorsal typmanic
recess and hence roofs the prootic depression.  Numerous fragments have
been suggested for the squamosal of _Archaeopteryx_.  Without entering into
the debate, the important fact is that, as both Whetstone (1993) and Walker
(1985) noted, it is unlikely that the squamosal of _Archaeopteryx_ could
have completely roofed the dorsal tympanic recess.

Another persistant problem is where the quadrate of _Archaeopteryx_
articulated on the skull (Whetstone 1983; Walker 1985). This debate again
is peripheral to the present focus.  In all cases the dorsal tympanic
recess would be rostral to the articulation of the quadrate with the skull,
as in _Enaliornis_, _Parahesperornis_, _Hesperornis_ and many moderd
birds." (p. 360-361)

I am taking Witmer's use of the term "rostral" in its zoological sense,
i.e. "of or pertaining to, situated in or upon".

Thus Witmer appears to be saying that the dorsal tympanic recess is
situated in the articulation of the quadrate. Having said in the previous
paragraph that the dorsal tympanic recess is *not* composed *only* of the
squamosal, it seems to me suggestive that more than one bone is involved in
the articulation.

I could be mistaken about Witmer's usage of the word "rostral" - he may
have meant "near", but I could find no published criticism of Whetstone's
placement of the cotyle. [note: a major reference pertinent to this issue
is Walker 1985 in the book "The Beginnings of Birds". I do not have access
to this reference.]

If anyone knows of any, I would be grateful if they would let me know.

Chris

Currie, P.J. (1985) Cranial anatomy of _Stenonychosaurus inequalis_
(Saurischia, Theropods) and its bearing on the origin of birds. Canadian
Journal of Earth Sciences, 22: 1643-1658.

Currie, P.J. & Zhao, Xi-Jin (1993) A new troodontid (Dinosauria, Theropods)
braincase from the Dinosaur Park formation (Campanian) of Alberta. Caadian
Journal of Earht Sciences, 30: 2231-2247.

Witmer, J.M. (1990) Craniofacial pneumaticy in Mesozoic birds. Zoological
Journal of the Linnean Society, 100: 327-378

cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
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