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Re: Monoclonius recurvicornis..a new generic name



Lukas Panzarin (heby@libero.it) wrote:

<Monoclomius recurvicornis is one of the forgotten species named by Cope
(based on 3 horn, a braincase, and an occipital condylum); however, the
generic name is wrong: this animal was another kind of animal. The "M."
recurvicornis is often regarded as an indeterminate ceratopsid, but the
fragmentary holotype have some truly intriguing character present in no
other ceratopsid. Although the specimen is a subadult, the shape and
dimension of the horns are totally different from any other centrosaurine
or chasmosaurine. The suprahorbital horn are 210 mm high, completely
erect, and slighty procurved, totally different from Chasmosaurus (the
only chasmosaurine with short supraorbital horn), and only superficially
similar to the new Montana centrosaurine. Moreover, the orbital horn
appear to be born from a separate center of ossification (this feature
would be unique in ceratopsian kingdom). The nasal horn is a small version
to that of Einiosaurus, and like other subadult centrosaurine, the horn is
split in two halves. In front of right eyes there is an unespected
formation: a small procurved hornlet; the left side is no preserved, so
one can?t tell if that horn was pathologic. Unfortunately the frill is no
preserved. 

[...]

This animal should be renamed under another generic name, ?cause is
totally different from Monoclonius sensu stricto (indeterminate
centrosaurines based on subadult of Centrosaurus and Styracosaurus).>

  *Monoclonius procurvicornis* has been considered a junior synonym of
*Centrosaurus apertus* for some time, as specimens and further skulls of
*C. apertus* have shown a variety of orientations and shapes of the nasal
and orbital horncores. Orbital horncores in several ceratopsids, including
*Centrosaurus,* *Einiosaurus,* and several new centrosaurs in press, show
that they form from separate ossification centers than chasmosaur horns,
usually in the middle of a pit that developes a triangular horn core.

  *C. apertus* skeletons show small and long nasal horns with
forward-curving, straight, or even back-curving shapes, relatively large
to no orbital cores, and slight variation in the frill horns and
epoccipital "horns." This suggests that variation among individuals and
genders may account for the variation in specimens, rather than between
species.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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