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R: Heterodontosaurids

-----Messaggio originale-----
Da: jconrad@lib.drury.edu <jconrad@lib.drury.edu>
A: dinosaur@usc.edu <dinosaur@usc.edu>
Data: lunedì 3 maggio 1999 20.22
Oggetto: Heterodontosaurids

>Just looking at the old cerapod phylogeny and shaking my head about the
>placement of heterodontosaurids.  If you look at the jugal boss and
>caniniform teeth, don't you see basal pachycephalosaur?  Now if
>is a valid taxon and it does lack the caniniform teeth, wouldn't this be a
>good candidate for sister-group to Marginocephalia, perhaps something like:
>(_Lanasaurus_ (Ceratopsia (Heterodontosauridae + Pachycephalosauria)))
>The only reason I include ceratopsians in a group with
>"heterodontosaurids"/pachycephalosaurs exclusive of _Lanasaurus_ is
>of the caniniform teeth in _Protoceratops_, which could be because of
>I understand that the idea of heterodontosaurids as basal members of
>Ornithopoda is beginning to lose favor, but have not seen a recent
>phylogeny where it was not considered so.  Things like _Hypsilophodon_
>more primitive in the brevity of the posteroventral projection of the
>premaxilla, retention of more than 3 premaxillary teeth, more primitive
>"cheek" teeth, and morphology of the quadratojugal, yet have been
>more advanced ornithopods than _Heterodontosaurus_.  Doesn't removal of
>latter from Ornithopoda seem most likely to be right?
>Just things to ponder (non-theropod too).

Yes, I think that Heterodontosauridae share with basal Pachycephalosauria a
jugal boss, three caniniform teeth and a maxilla/premaxilla diastema, but if
you can observe this features is also share by some basal NeoCeratopsia,
infact Protoceratops and Breviceratops have three caniniform teeth and
apparently all Ceratopsia have a jugal boss and a maxilla/premaxilla
I don't known for Lanasaurus, because I don't have material about this taxa,
but I think that all Heterodontosauridae is a good candidate for a
sister-group to Marginocephalia
And what about Chaoyangosaurus?
Is a more basal Ceratopsia like Psittacosaurus or is an intermediate taxa
between Pachycephalosauria and Ceratopsia?

Alessandro Marisa
"Voluntary of Paleontology Group of Monfalcone"
Via Achille Grandi n°18
Tel: 039-0464-434658 Email: amaris@tin.it