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

re: what's wrong with Jouve's Ctenochasma?



Rutger is correct, and incorrect. There's an unexpected twist to this
story.

The Saint-Dizier specimen is a match for the skull crushed
dorsoventrally [PTHE 1951.84 (Mayr 1964, No. 70 of Wellnhofer 1970,
1991)] that has come to be considered the icon for Gnathosaurus ? and
not a match for  B St 1935 I 24, No. 65 of Wellnhofer 1970, Specimen 3
of Buisonjé 1981 the completely articulated specimen that has come to be
known as the icon for Ctenochasma.

But the Saint-Dizier specimen _does match_ the Ctenochasma holotype, a
large toothy mandible.

Remember, the mandible of Gnathosaurus (the holotype specimen) is not
spoon-billed either, just the rostrum is.

A reconstruction of the Saint-Dizier specimen apppears at:
www.pterosaurinfo.com/saintd_gnathosaurus_recon.html

Overall the size of the Saint-Dizier specimen is a good match for No. 70
and a third smaller than the Ctenochasma holotype, according to Jouve.

Characters in the Saint-Dizier specimen matching No. 70 and not matching
No. 65:
The antorbital fenestra is larger than the orbit. The orientation of the
jugal, which cannot be compared to No. 70 is angled higher than in No.
65 and similar to more primitive taxa. The upper temporal arch is as
high as the orbit, as opposed to No. 65, where it is considerably lower.
The teeth may not be as robust as in the dorsoventrally crushed skull,
but another gnathosaurine, Plataleorhynchus, has even more gracile
teeth.

Note the broad nasals overlap the premaxilla dorsal to the antorbital
fenestra (mislabeled the premaxilla), as in all Ctenochasmatids. The
premaxilla is overlapped anteriorly by the maxilla, again as in all
Ctenochasmatids. The lacrimal is a broad plate (mislabeled the nasal),
so the mysterious nasal fenestra becomes the more typical lacrimal
fenestra.

Some other labeling errors:
Fig. 1: The "prefrontal" is a part of the nasal. The real prefrontal is
over the orbit.
Fig. 2: The right quadratojugal is the postorbital process of the jugal.
The post orbital is too low in the tracing. The actual PO is just above
it.
Fig. 4. The "brain" in the Saint-Dizier specimen is much too small.
Fig. 9. Jouve points to the uneven ventral margin of the dentary in a
specimen labeled, Pterodactylus "kochi" B St 1878 VI 1 [No. 13 of
Wellnhofer 1970] as an example of a fossilization artifact, but it is
not. Instead this character is a genuine feature and the genesis of the
deep mandible found in some Nyctosaurus and Pteranodon.

Jouve states that P. antiquus [BSP Nr. AS I 739, No. 4 of Wellnhofer
1970] and P. kochi [B St ASXIX 3 (plate). SMF No. R 404 (counterplate).
No. 23 of Wellnhofer 1970]
represent two different growth stages of single species.  The holotypes
of both can be found at pterosaurinfo.com/p_antiquus_recon.html and
pterosaurinfo.com/no23_recon.html for comparison. There's no comparison,
although I would imagine that Jouve is not considering the holotype, but
rather the referred specimens of P. kochi, that we're all familiar with
that are closer to No. 4.

C. porocristata or porocristatum will turn out to be closer to
Huanhepterus and the azhdarchids in a paper coming soon. So it is
unrelated to Ctenochasma.

Dr. Christopher Bennett is acknowledged  for "numerous suggestions,
comments and criticisms [which] improved this work significantly."

The nomenclature problem which Jouve has unintentionally unearthed is
interesting. Ctenochasma roemeri (Meyer 1852) is the holotype specimen.
As Jouve noted, it is quite similar to the Saint-Dizier specimen.
Working backwards, that means that our traditional "Gnathosaurus" No.
70, may really be Ctenochasma. And our traditional Ctenochasma, No. 65,
may have to be renamed.

David Peters