Re: Hongshanosaurus houi, new psittacosaur

["Jaime A. Headden" <qilongia@yahoo.com>]

George Olshevsky (Dinogeorge@aol.com) wrote:
 
<Echinodon doesn't have the premaxillary tooth pattern shared by 
heterodontosaurs and later marginocephalians (the premax teeth are lost in
most ceratopians but one or two are still there in Protoceratops and some
Psittacosaurus species), so I'd place it in a sister group to the others.>

  This point has been raised before. However, only one possible species of
*Psittacosaurus* has been found with premaxillary teeth, and this is
undescribed at present. *Chaoyangsaurus* has two teeth, and in recent
analyses remains a basal ceratopsian. *Liaoceratops*, more dervied than
*C.*, has three premaxillary teeth. They are convergently lost in
leptoceratopsids and ceratopsoids in most phylogenies, or a shared
acquired feature in the recent You and Dodson paper on *Archaeoceratops*
(which has two premaxillary teeth).

  However, unless *Heterodontosaurus* is a pachycephalosaur or
ceratopsian, it does not satisfy the original cladistic definition and
continuing useage of Marginocephalia = {*Pachycephalosaurus* +
*Triceratops*}; if it the sister group to these taxa, it cannot be a
marginocephalian.

  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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