Re: Yandusaurus multidens in SVP2003 abstracts

["Tim Williams" <twilliams_alpha@hotmail.com>]

jigruiz@unizar.es wrote:

> "Y." multidens was originally referred to the Hypsilophodontidae on the 
> basis
> of similarities apparently shared with Dryosaurus (a taxon then thought to 
> be a
> close relative of Hypsilophodon). Subsequently, various authors have either
> supported this referral or regarded "Y." multidens as a fabrosaurid or 
> basal
> ornithischian. Although "Y." multidens is definitely more primitive than 
> the
> dryosaurid Dryosaurus, its phylogenetic position amongst ornithopods 
> remains
> challenging. Cladistic analyses suggest that Agilisaurus louderbacki and
> Othnielia rex may be the sister taxa of "Y." multidens.

Thank you for a very interesting post.  I have seen _Y. multidens_ called 
_Agilisaurus multidens_.  I would addd that further complicating the 
taxonomy of this group is the status of the genus _Xiaosaurus_.

A monophyletic Hypsilophodontidae is looking a little shaky these days, and 
not just on account of the position of 
_Othnielia_/_Yandusaurus_/_Agilisaurus_.  It has been suggested that some 
Australian "hypsilophodontids" (_Atlascopcosaurus_, _Qantassaurus_) may be 
closer to their larger compatriot _Muttaburrasaurus_, and thus represent an 
endemic clade of Aussie ornithopods.

I also wonder if some of the taxa thought to be fabrosaurids or basal 
ornithischians might prove to be basal marginocephalians - before they 
"bloomed" into the pachycephalosaurs and ceratopsians.



Tim

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