[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

re: ctenochasmatid pmx tooth count



A short while back there was some discussion regarding ctenochasmatid
premaxillary tooth counts -- especially as to how the count might relate
to the familial identity of the South American pterosaur, Cearadactylus
atrox. Unwin (2002) wrote that 7 pairs of pmx teeth were present in this
taxon.

Howse and Milner 1995 described a gnathosaurine (spoonbill)
ctenochasmatid rostrum purportedly exposed in ventral view. They
dilineated sutures and cracks thereon in a pair of illustrations -- the
left an interpretive drawing of the rostrum insitu and the right a
reconstruction. At least 8 pairs of teeth were identified on the rugose
palatal portion of the "premaxilla" but they noted that the pmx/mx
sutures could not be clearly identified.

I was drawn to this paper over the weekend because in all the other
ctenochasmatids, and all the other pterosaurs for that matter, four
premaxillary teeth is the standard number. Three, two or zero appear in
certain ornithocheirids, germanodactylids and sword-nosed forms
(pteranodontids, tapejarids and nyctosaurids) respectively. The detailed
drawings of Howse and Milner were compelling, but a scan of the
accompanying photo proved otherwise.

In my interpretation of the rostrum the exposure is in dorsal view, not
palatal view. Premaxillary and maxillary sutures can be seen clearly
enough to make a map of the rostrum (available by private request). The
premaxillary sutures encompass only the four anterior teeth per side, as
in others of its clade, making the premaxilla essentially transverse in
its jawline exposure, as in other ctenos. The rugose texture ascribed to
the premaxilla is suddenly no mystery -- it's the dorsal surface of the
bone. Perhaps the authors were not prepared for the wrapping of the
maxilla over the premaxilla at the "neck" of the spoonbill, but this is
a synapomorphy of the Ctenochasmatidae + AMNH 1942, a pterodactylid
until now ascribed to P. antiquus. Finally, at the proximal part of the
rostrum, a portion of the mandible with alveoli, slighly narrower than
the rostrum, appears below a break in the rostrum. It would have been
tough to explain how the mandibles became "dorsal" to the rostrum.
Perhaps that is why they were virtually ignored in the paper.

Scanning does help.

I don't know if this negates the validity of the taxon Plataleorhynchus
or not. If anyone has a picture of the dorsal rostrum of Gnathosaurus
they could send or copy, I'd appreciate it.

Still attempting to demystify the Pterosauria ~
David Peters
St. Louis