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Re: Yandusaurus multidens in SVP2003 abstracts
"Y." multidens was originally referred to the Hypsilophodontidae on the
of similarities apparently shared with Dryosaurus (a taxon then thought to
close relative of Hypsilophodon). Subsequently, various authors have either
supported this referral or regarded "Y." multidens as a fabrosaurid or
ornithischian. Although "Y." multidens is definitely more primitive than
dryosaurid Dryosaurus, its phylogenetic position amongst ornithopods
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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