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Genusaurus sisteronis



Having received photocopies of the following article from Tom
Holtz and Tracy Ford, and an original offprint from Fred
Bervoets, I decided it was time to take a closer look at the
taxon being described therein:

Accarie, H., Beaudoin, B., Dejax, J., Fries, G., Michard, J.-G. &
Taquet, P., 1995. "Decouverte d'un Dinosaure Theropode nouveau
(_Genusaurus sisteronis_ n. g., n. sp.) dans l'Albien marin de
Sisteron (Alpes de Haute-Provence, France) et extension au
Cretace inferieur de la lignee ceratosaurienne," _Comptes Rendus
Acad. Sci. Paris 320_, serie IIa: 327-334 [in French with
abridged English text; certain characters in the authors' names
and title above include diacritical marks, which I have omitted
because they cannot be transmitted via e-mail].

The new theropod is from the middle Albian of Bevons, 4.25 km
southwest of Sisteron, Alpes de Haute-Provence, and the material
includes mainly pelvic and hind-limb elements from the left side:
ilium, proximal part of pubis, femur, proximal part of tibia, and
proximal part of fibula. A tarsal bone, a sacral vertebra, and
seven dorsal centra are also among the remains. At first I didn't
see the tibia in the photographs, because I thought I was looking
at a femur in cranial or caudal view: the cnemial crest is so
strongly developed that it resembles an offset femoral head(!).
Hence the generic name _Genusaurus_: "knee lizard." The femur is
38 cm long, which suggests a length of about 4 meters for the
whole animal and a height of about 1.5 meters at the hip.

Several diagnostic features of the pelvic and limb elements,
summarized in the English text, indicate that _Genusaurus_
belongs to the clade Ceratosauria. If this is true, _Genusaurus_
was a derived form in which the femur was not vertical but was
inclined cranioventrally from the acetabulum, as in ratite birds.
Whether this means it had a shorter tail than most theropods is
not known. The low, elongate, caudally well-developed ilium, is
likewise unique, resembling the corresponding elements of ratite
birds more than those of theropods.

Well-developed cnemial crests occur in most theropods, so by
itself the crest of _Genusaurus_ is not taxonomically
significant. My own comparison with the hind-limb elements of the
abelisaurid _Xenotarsosaurus_ shows a well-developed cnemial
crest similar to that of _Genusaurus_ (though differently
shaped), and a well-developed cnemial crest is also found in
_Carnotaurus sastrei_. I conclude that _Genusaurus_ is not just a
ceratosaurian but a neoceratosaurian that may provisionally be
referred to the family Abelisauridae. At least, this possibility cannot
be eliminated based on the available material.

G.O.