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Re: What's wrong with Jouve's Ctenochasma?



The JVP arrived yesterday, and I've read that article. I haven't found a
mistake so far, except that like everyone before him Jouve doesn't mention
that *C. porocristata* should be *C. porocristatum* -- chasma is neutral
(one of those Greek -ma words that become -mata in the plural... plasma...
problema... dilemma... chiasma...), *C. gracile* is correct.

Interestingly, this paper seemingly represents part of his... DEA... let's
call it a Master's thesis from 2000. The latter also contains a phylogenetic
analysis and seemingly more ontogenetic work than the new paper.

----- Original Message -----
From: "fam jansma" <fam.jansma@tiscali.nl>
Sent: Wednesday, October 06, 2004 8:22 AM

> When I first glanced over the photographs of the specimen, I noticed how
low
> in number the dentary teeth, or, the empty toothsockets where, at least
when
> you compare it to the lower jaw in Wellnhofer's book that is certainly
> Ctenochasma. Instead, the amount of teeth that would have fitted into
these
> sockets is a more close match to Gnathosaurus. So, based on tooth count, I
> would suggest we have got ourselfs a true lateral view of Gnathosaurus! :)

The teeth are still more in number and less robust than those of
*Gnathosaurus*. Below is a summary of the article:

Stéphane Jouve: Description of the skull of a *Ctenochasma* (Pterosauria)
from the latest Jurassic of eastern France, with a taxonomic revision of
European Tithonian Pterodactyloidea, JVP 24(3)542 -- 554 (September 2004)

Abstract:
"A *Ctenochasma* specimen from the latest Jurassic of eastern France is
described in detail and referred to *Ctenochasma* sp. The preserved
braincase of this specimen has a bird-like lateral position of the optic
lobes, with proportionally a smaller size than in birds, the bones
surrounding it being thick and hollow.
    An original biometric analysis, based on skull length and tooth number,
has been performed using a selection of Late Jurassic Pterodactyloidea of
Europe. This study suggests that *Ctenochasma gracile* and *Ctenochasma
porocristata* are senior [wrong, junior!] synonyms of *Pterodactylus
elegans*[,] and *Pterodactylus antiquus* of *Pterodactylus kochi* [really
senior this time]. It also reveals that *Pterodactylus elegans* may be
transferred to *Ctenochasma*. These results obtained with biometric analyses
are confirmed by morphological observations. This study could not determine
if *Pterodactylus micronyx* is a juvenile of *C. roemeri* [the type
species], the *Ctenochasma* of Saint Dizier or *Gnathosaurus subulatus*.
Because this species is only composed of juveniles, more data are needed to
determine its adult morphology. The genus *Ctenochasma* is thus represented
by three species, *C. elegans*, *C. roemeri* and *C.* sp., and
*Pterodactylus* by two, *P. antiquus* and *P. longicollum*, all from the
Late Jurassic of Germany and France. This study points out a biological
anomaly: all the teeth are not present in a hatching pterosaur [probably
means: not all teeth are present...], but their number increase[s]
progressively during growth, with new teeth erupting from the front of the
jaws. This phenomenon is particularly spectacular in *Ctenochasma elegans*,
where the tooth number increases progressively from 60 to more than 400
teeth during growth."

The reason for why the new species is not named is never mentioned. Probably
it is the fact that it could be a synonym of *"P." micronyx*.

The olfactory bulbs seem to have been located in front of the eyes, not
behind them as in birds. Jouve does not feel very certain about this,
however. Anyway, lots of interesting stuff about pterosaur braincases.

p. 547:
"The Ctenochasmatidae includes two genera, which are mainly differentiated
by the number and shape of their teeth (Wellnhofer, 1970, 1978):
*Ctenochasma* Meyer, 1852, has thin and numerous teeth (200 to 360), that
are equal in size anteriorly, becoming gradually shorter posteriorly,
whereas *Gnathosaurus* Meyer, 1834, bears 128 -- 136 long, but more robust
teeth, the size of which decrease[s] quickly in the caudal 80% of the length
of the tooth row.
    On the basis of its thin and very numerous teeth (more than 200), and
the progressive decrease of the tooth size posteriorly, the Saint-Dizier
specimen can be referred to *Ctenochasma*. Three species of *Ctenochasma*
have been described: (1) *C. roemeri* Meyer, 1852, known only by the
anterior part of a single lower jaw, has 200 closely set and relatively
robust teeth [...]; (2) *C. porocristata* Buisonjé, 1981, known from the
anterior part of the skull, as 408 very thin teeth; (3) *C. gracile* Oppel,
1862, the best documented species represented by several specimens has 360
thin teeth (for the largest specimen) close to *Ctenochasma porocristata*
ones [...].
    The Saint-Dizier *Ctenochasma* has a skull one-third smaller than
*Ctenochasma roemeri*, but has the same tooth count, and similar dental
morphology (Appendix 1), with differences in size (about 20 mm for *C.
roemeri* and 14 mm in *C.* sp.) and space between the teeth (1.5 to 2 mm in
*C. roemeri*, and 1 mm in *C.* sp.). On the other hand, its tooth count is
smaller than that of the biggest specimen of *Ctenochasma gracile*, despite
its larger skull size. The Saint-Dizier specimen has the same skull size as
*Ctenochasma porocristata*, but half as many teeth (Appendix 1).
Furthermore, the teeth of *Ctenochasma* sp. are more robust than those of
*C. gracile* or *C. porocristata*, and its upper tooth row extends far
behind the level of the mandibular symphysis in the Saint Dizier specimen,
whereas there is a large distance between the last posterior teeth and the
[caudal end of the] symphysis (small specimen, Wellnhofer, 1970:pl. 11, Fig.
3) or the tooth row stops at the level of the symphysis in *C. gracile*
(large specimen, 1920 I 57, Broili, 1924).
    The specimen described here cannot be referred to the three extant
[er... existing?] species. Nevertheless, it can be noted that both the
largest specimens of *C. gracile* and *C. porocristata* share some
similarities (thickness and size of teeth), indicating that the second
species could be considered as an adult of the first. The same problem
applies to all European Tithonian Pterodactyloidea, especially for the genus
*Pterodactylus*, for which some species of smaller size occur in nearby
deposits (Mateer, 1975; Bennett, 1992, 1993, 1996b, 2002)."

Emended diagnosis of *Ctenochasma elegans* (Wagner, 1861), p. 548:
"Pterodactyloidea with numerous (more than 400 in adult), closely-spaced,
very long and extremely slender teeth, which are laterally directed, forming
a basket. The more posterior teeth reach the level of the anterior margin of
the nas[...]antorbital fenestra. Very slender and extremely elongated snout,
nas[...]antorbital fenestra short; mandibular tooth row ends at the level of
the symphysis; moderate length neck, short metacarpal IV, long wing phalanx
1, short femur."

Diagnosis of *Pterodactylus antiquus* (Soemmering, 1812), p. 549f.:
"Pterodactyloidea with an elongated skull whose the [sic] dorsal margin is
straight; slender and elongated snout; fenestra nasoantorbital [sic] length
about twice that of the orbit; approximately 90 conical and robust teeth;
upper tooth row reaches or extends posterior to the level of the anterior
margin of the nas[...]antorbital fenestra; nasal process very slender and
perpendicular to the maxilla."

*P.* sp. described by Frey & Tischlinger (2000) is also synonymous with *P.
antiquus*.

*P. longicollum* is different from *P. antiquus*, because it has a concave
(not straight) dorsal skull margin, a nasantorbital fenestra just a little
longer than (not ~ twice as long as) the orbit, lacks a long nasal process
within that fenestra, has longer and more slender teeth, and has a shorter
tooth row -- it ends "well anterior to the anterior margin of the
nas[...]antorbital fenestra, when the tooth row ends at the level of or
posterior to the anterior margin of the nas[...]antorbital fenestra in *P.
antiquus*" (p. 550).
    "For *Germanodactylus*, the differences are more important, with a
shorter distance between the tip of the snout and the anterior margin of the
nas[...]antorbital fenestra [...] than in *P. antiquus* [...]. The quadrate
is less inclined compared to the anterior base of [the] skull in
*Germanodactylus*, and the nas[...]antorbital fenestra is higher
posteriorly, with a more triangular shape than in *P. antiquus*. Therefore,
the *Germanodactylus* are two distinct species from *P. antiquus*."

*Cycnorhamphus* is clearly something different.

And now the evidence for all the synonymy. It rests primarily in the graphs,
fig. 7, 8 and 10. They plot the skull length of individual specimens versus
their tooth number. Fig. 10 includes the nominal species *P. micronyx*, *C.*
sp., *C. roemeri* and *Gnathosaurus subulatus*, fig. 8 includes *P.
elegans*, *C. gracile*, *C. porocristata*, *P. kochi*, *P. antiquus*, *P.*
sp., *Germanodactylus rhamphastinus*, *G. cristatus* and *P. longicollum*.
Fig. 7 includes both sets. It becomes clear that:
- *C. porocristata*, *C. gracile* and *P. elegans* (from biggest to
smallest) lie on the same straight line which is much steeper than all
others;
- *C.* sp. is quite distinct from everything else;
- *P. antiquus*, *P.* sp. and *P. kochi* lie on the same straight line;
- the affinities of *P. micronyx* stay unclear within fig. 10 because only 1
large specimen is known of *C. roemeri* and *C.* sp. each, and only 2 large
one of *Gnathosaurus*, while all 6 that are referred to *P. micronyx* are
quite small;
- a straight line (not shown) could be drawn through *P. longicollum*, *G.
rhamphastinus*, *G. cristatus* and *P. kochi*.

Why should tooth number increase with skull length within a species? The
discussion of *C. elegans* (p. 548) makes a convincing argument for this and
against various characters that were considered diagnostic in earlier times:
    "The skull of *Pterodactylus elegans* exhibits juvenile characters such
as large orbits compared to the skull length, a nas[...]antorbital fenestra
much smaller than the orbit, and very thin teeth, which are restricted to
the anterior part of the jaws. In *C. gracile* the snout is more elongated,
the nas[...]antorbital fenestra larger, and the tooth row more extended
posteriorly. In *C. porocristata*, the teeth extend much farther
posteriorly, reaching the anterior level of the nas[...]antorbital fenestra.
When Buisonjé described *C. porocristata*, the possibility than [sic] t was
an adult of *C. gracile* was first considered but later rejected with the
arguments that *C. porocristata* possesses more teeth, a larger skull, a
relatively longer maxillary toothed area, a broader beak and, of particular
importance, a premaxillary crest. Buisonjé regarded the premaxillary crest
as an important taxonomic character, following Wiman (1925) who separated
*Germanodactylus cristatus* and *Pterodactylus kochi* into two species on
the basis of this feature. Other morphological characters (teeth [sic]
number, skull length, maxillary teeth area and beak development) increase
progressively during ontogeny (Edmund, 1969; see below). The premaxillary
crest is probably a character that appears late during ontogeny or, as
suggested by Bennett (1992), a sexual character. In crocodilians, the teeth
appear from front to back during embryogenesis, and all the total number of
tooth of adult [sic] is present in the hatching animal (Edmund, 1960, 1962,
1969). In *Ctenochasma*, the teeth probably appear from the front to the
back of the jaws during embryogenesis, as in crocodilians, but due to the
high tooth count, the phenomenon continues for a long time after the
hatching. This explains the posterior elongation of the tooth row during its
growth, represented by the three stages *P. elegans*, *C. gracile* and *C.
porocristata*."

Other cranial characters, as well as postcranial ones from Bennett 1996b,
are used to support the synonymy of the three "species". Likewise, all
differences between *P. antiquus* and *P. kochi* are considered ontogenetic
(tooth size, tooth count, skull length, neck length, size of antorbital
fenestra). The largest specimens of *P. antiquus* are only considered
subadult, however.

p. 551:
"CONCLUSIONS

    This study using an original method of analysis provides a basis for a
taxonomic revision of late Jurassic Pterodactyloidea of Europe, supporting
the validity of the species *C. elegans* and *P. antiquus*. More data are
needed to resolve the possible synonymies of the remaining taxa[.]
    According to the results of the analysis, the genus *Pterodactylus* is
composed by [sic] only two species (*Pterodactylus antiquus* and
*Pterodactylus longicollum*), whereas the genus *Ctenochasma* includes three
species (*Ctenochasma roemeri*, *Ctenochasma elegans*, and *Ctenochasma*
sp.), and *Germanodactylus* is a valid taxa [sic].
    The systematics of pterosaurs does not seem definitely established,
since a simple statistical study determined the synonymy between some
species: *Pterodactylus elegans*, *Ctenochasma gracile* and *Ctenochasma
porocristata* on the one hand, *Pterodactylus antiquus* and *Pterodactylus
kochi* on the other hand. Some problems remain with *P. micronyx*, a species
composed only of juveniles, but it is not possible to determine if the adult
form is *C. roemeri*, *C.* sp., or *Gnathosaurus subulatus*."