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RE: Megalosaurus and Titanosaurus



I just read the new Allain and Chure paper on *Poekilopleuron bucklandii*,
and would only like to further comment on some facts listed for the
Stonesfield material in relation to diagnosis of *Megalosaurus*:

[pg. 1117]

"The lectotype specimen of *Megalosaurus bucklandii* (Molnar et al. 1990;
Benton and Spencer 1995; Rauhut 2000) is the rostral portion of a right
dentary with teeth (OUM-J13505). As specified by Buckland"

[pg. 1118]

"(1824) and pointed out by Cuvier (1824) and Owen (1856), the bones
discovered at Stonesfield were neither found together in one spot nor
associated. At present, no convincing case has been made that all the
Stonesfield theropod material referred to *Megalosaurus* actually belongs
to that taxon, and we view with some skepticism the assignment of other
non-associated material to the species represented by the dentary (see
Buckland 1824 and Glut 1997, pp. 587-592 for details of this material)."

  Further sentences go on to describe the recent Morrison diversity and
that of the Lourinha beds, and how "it is not out of the question that
several large theropods may have co-existed in Europe during the Mid
Jurassic."

They go on:

"Contrary to what was previously reported (Molnar et al. 1990), three
theropods, two of which are large, have been recovered in Stonesfield, as
shown by the three different ilia housed in the collections of The Natural
History Museum and Oxford University Museum. The smallest one (BMNHR83)
was referred by Huene (1932, pl. 3, fig. 2) to *Iliosuchus incognitus*.
The other two described by Buckland (1824, p. 43, fig. 3; OUM-J13560) and
Owen (1856, pl. 15, not figured; BMNH31811) were both referred to
*Megalosaurus bucklandii*, but they are quite different from one another
in shape and proportions. Similarly, a femur from Stonesfield referred to
*Megalosaurus bucklandii* by Owen (1856, tables 7--8; BMNH31806) is
straight in medial view with a medially directed femoral head, while that
described originally by Buckland (1824, pl. 44, figs. 1--2; OUMJ13561) is
strongly sigmoid with an anteromedially directed femoral head, similar to
that of *Ceratosaurus nasicornis* (Gilmore 1920, p. 109). Finally,
Phillips (1871, p. 208) reported 'there are in reality two forms of
scapulae in the Oxford collection placed in the megalosaurian series, one
of which is ancylosed to the coracoid, the other not so. They differ
enough to be certainly referable to different species of animals, the
second mentioned being of larger size.'"

  The authors then sum-up:

  "Although numerous other skeletal parts have been referred to
*Megalosaurus bucklandii* (Owen 1856; Huxley 1869; Phillips 1871; Walker
1964; Molnar et al. 1990; Britt 1991; Padian 1997), these elements are of
uncertain relationship to the type dentary and the status of the genus
must hinge on the dentary alone."

  Finally, considerations on the validity of the name, continuing in the
same paragraph:

  "Our examination of the dentary does not reveal any diagnostic features
as noted by Molnar (1990). We consider the genoholotypic specimen of
*Megalosaurus bucklandii* a _nomen dubium_ and recommend that the name
*Megalosaurus* be restricted to the dentary (OUMJ13506), pending thorough
taxonomic revision in progress by L. Canning, P.M. Barrett and P. Powell.
Since there is no dentary material of *Poekilopleuron bucklandii*, the
synonymy between *P. bucklandii* and *Megalosaurus bucklandii* cannot be
determined."

  The whole issue of relation of elements to *megalosaurus* appears based
on some major-leage assumptions on how a single quarry can produce a
single animal or single _type_ of animal, a condition which appears to be
very, very false, even upon examination of the various elements. The two
scapulae mentioned above showed a smaller, fused scapulocoracoid versus a
larger, separate pair of elements. One femur is more primitive than that
which appears to be "spinosauroid", and may ceratosaurian, but this is
preliminary.

  The authors also note that the use of "Megalosauridae" is simply
contemporary, rather than explicit, as in the recent Allain JVP paper, and
it should be taken as _very_ subject to change.

----

  Just like to add to the list of types: a genoholotype is a specimen
which is the type for both the species _and_ the genus, as compared to
that of a referred species. By similar name, but not meaning, a genotype
is the genetic type of a species, lately in use by neontologists defining
extant animals, where it is drawn from the type specimen.


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