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Re: dino quadrates



GSPaul wrote:

>There is no socket for the quadrate known in the skull of the London Arch.
>yet

"The fenestra ovalis lay immediately ventral to the facies articularis pro
quadrato as in most Recent birds.  The dorsal margin of the fenestra is
formed by the prootic, which appears to contribute to the anterior portion
of the cotyle for the quadrate [note: cotyle means "cup" or "cup-shaped"].
The fenestra pseudorotunda is located more ventrally.  Its margins are
poorly defined.  The posterior boundary is formed by a process of the
otoccipital which extends ventrally from the posterior part of the quadrate
cotyle." (Whetstone 1983, p. 447)

"The posterior part of the tympanic cavity is formed by the otocicipital (a
term which presumes that the bone is formed, as in Recent birds, by the
fusion of the exoccipital and opisthotic).  This bone forms a prominent,
oval cotyle for articulation with the quadrate.  There is no sharpe
posterior boundary to the cotyle.  The articulatory surface is structurally
continuous with the dorsal part of metotic crest, a narrow ridge of bone
extending ventrally from the paroccipital process.  Anteroventrally, the
cotyle terminates with a thickened, rounded edge at the posterodorsal
margin of the otic cavity.  Dorsally the cotyle has been crushed into the
overlying prootic.  Because of the fragmentation of the bone, it was not
possible to prepare all of the matrix from this area.  The anterodorsal
part of the cotyle is preserved under the prootic buttress.  This part of
the cotyle is formed by the prootic." (Whetstone 1983, p. 447).

I may have misinterpreted Whetstone (bones are not my strong suit), or
Whetstone's interpretation may have been challenged and shown to be in
error, in which case I would welcome corrections - but these quotations
appear to support the presence of a quadrate cotyle (or articulation) in
the skull of the London Specimen.

>To see how useless the CT images are of the Eichstatt spec just look up the
>paper in Paleobiology

I have seen the paper and agree that the interpretation is highly
speculative.  Nevertheless, the opinion is in the scientific literature and
thus must be addressed on a scientific basis (wheter we agree with it or
not).

Chris

cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
-------------------------------------------------------------------
Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong,
it was all downhill from there.