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re: the short-toothed ctenochasmatid



Chris Bennett wrote:

>>
I realize that I have not "use[d] the camera, computer, mouse and pen to

make my own drawings from which to make conclusions" but have instead
used
the highly unreliable method of actually examining the specimen under a
binocular microscope.  Moreover, I have only repeated those unreliable
observations twice (in 1993 and 2002).  However, both times I found
evidence
that convinced me that de Buisonje was right and the teeth were broken
off.
The broken ends of the untapering cylindrical teeth embedded in the jaw
were
pretty hard to miss.  Now maybe if I took a low resolution photo,
scanned it
into a computer, used lots of descreen followed by lots of sharpen,
traced
every feature of the specimen and surrounding matrix, and then tried to
interpret it in some way contrary to my actual observations, well then
maybe
I could see the light and agree with David Peters.
<<

Thank you, Chris, there is no doubt that the long premaxillary teeth (4
per side) have broken off. It appears however, that most of the
maxillary teeth are quite short, as in Angustinaripterus. Gnathosaurus
also shares this feature for almost two thirds of its rostrum.

The other interesting aspect is that the "bump" that Buisonjé found
appears to be the middle of the broken premaxilla which is then
continued unbroken back to the radically shifted skull roof (nasal,
lacrimal, frontals, parietals, postorbitals and sclerotic ring.) The
intact skull roof now lies anterior to the ectopalatines and the end of
the tooth rows. It is easy to see that both parts of the premaxilla run
parallel with each other in the middle of the skull. So rather than just
preserving the rostrum and ectopalatines, as Buisonjé illustrates,
practically the entire skull is preserved?as usual.

A slender crescentic maxillary ascending process is present. What that
means regarding separation of the naris and antorbital fenestra is yet
to be reconstructed, but it seems possible at present that the
antorbital fenestra was much larger than in a typical ctenochasmatid and
more like that of a more basal pterodactyloid or the higher
pre-pterodactyloids, like Pterorhynchus and Angustinaripterus. If so,
that would explain how the skull roof could shear off and occupy the
space that it does.

I imagine Dr. Bennett saw the same. I'd be glad to send tracings when
they're finished if not.

The "bump," if present, would be a cladistic anomaly because
Gnathosaurus has the standard narrow striated crest common to other
basal pterodactyloids.

Finally, the ectopalatine is much more robust than in either Ctenochasma
or Gnathosaurus. More like that of Pterorhynchus. My guess is that this
may be the most basal ctenochasmatid and one more clue that the
pterodactyloidea may be diphyletic (still a long shot, but worth
considering).

David Peters
St. Louis