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Re: Yandusaurus multidens in SVP2003 abstracts

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.


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