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Is DMNH 33365 Stegosaurus stenops?



Dear List-Members:
some time ago I've received the Carpenter's new book "The Armored
Dinosaurs", and my attention was focused on the Hesperosaurus mjosi's
description, expecially in the draw present on pag.62 (Figure 3.4). In it
there is a presumed (?in my opinion?) skull of Stegosaurus stenops
numbered DMNH 33365, well, if we compare this skull with that of Stegosaurus
stenops (USNM 4934 (Gilmore 1920)) we can see a lot of difference: (1) The
relative proportion of the length/height of DNMH 33365 skull agrees with
that of Hesperosaurus mjosi and Huayangosaurus taibaii than with of
Stegosaurus stenops: (2) In DNMH 33365 the external naris is small as in
Huayangosaurus taibaii and Hesperosaurus mjosi not large as in Stegosaurus
stenops and other Stegosaurids (es. Chungkingosaurus jiangbeiensis and
Paranthodon africanus): (3) The caudodorsal process of the premaxilla is
short and broad in DMNH 33365 as in Huayangosaurus taibaii, not long and
thin as Hesperosaurus mjosi, Stegosaurus stenops and some other Stegosaurids
(es. Chungkingosaurus jiangbeiensis and Paranthodon africanus): (4) The
antorbital fenestra of DMNH 33365 is smaller than that of Huayangosaurus
taibaii and Hesperosaurus mjosi, but not absent as in Stegosaurus stenops
and others Stegosaurids (es. Chungkingosaurus jingheiensis, Tuojangosaurus
multispinus), at this point I want to point out that differences (1) and (4)
are cited by Dong (1990) as the primitive trend in the evolution of the
skull of Stegosaurs, infact Dong write: " Primitively, there is (are) one
(or two) supraorbitals, the skull is high, the facial region short and
narrow, both antorbital and mandibular fenestra are present. On the base of
the DMNH 33365 draw seem that there is only one supraorbital bone.
Moreover my friend Marco Auditore tell me that if we observe the mandible of
DMNH 33365 we can see that this element seem more similar to the same
element figured in
"The Dinosauria"  at pag.437 (Figure21.2 J-K-L). Unfortunately this mandible
is not numbered, but his posterior half  is very deep as seem in DMNH 33365
and is deeper than that of Stegosaurus stenops and also Huayangosaurus
taibaii and Hesperosaurus mjosi, moreover there is a mandibular fenestra not
present in the mandible of Stegosaurus stenops, but present in Hesperosaurus
mjosi and Huayangosaurus taibaii. If we take a look at the mandible CM 41681
assigned to Stegosaurus sp. by McIntosh and Berman (1986) (pag.32 Fig.1.) we
can see that the posterior half of CM 41681 is very similar to that in the
un-numbered mandible in "The Dinosauria", moreover in the CM 41681 there are
20 teeth position, the same number as in Hesperosaurus mjosi, not 23 as in
Stegosaurus stenops (USNM 4935). Well, in conclusion there is the
possibility that the DMNH 33365 skull represent a new taxa of Stegosaurids,
perhaps closely related to Hesperosaurus mjosi? and that the mandible in
"The Dinosauria" and CM41681 could referred to this taxa or to a taxa very
similar to it?
Comment are welcome?

By
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Marisa Alessandro
"Volounteer of Museo Paleontologico Cittadino, Monfalcone"
Via Achille Grandi n°18
38068 ROVERETO (TN) ITALY
Tel:039-0464-434658 Email amaris@tin.it
Museum Web-Page: http://www.fante.speleo.it
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