?Yandusaurus? multidens in SVP2003 abstracts

[jigruiz@unizar.es]

There are lots of dinosaur papers in the SVP2003 abstracts, downloadables in:

http://www.vertpaleo.org/meetings/VRPA2303supp_all.pdf

One of the most interesting for ornithopod´s friends is that of Knoll & Barret 
suggesting that ?Yandusaurus? multidens don´t pertain to the genus Yandusaurus, 
a topic previosly discussed in this list.

The ref is:

Knoll, F. & Barret, P. M. 2003. Systematic revision ff "Yandusaurus" Multidens, 
a Middle Jurassic Ornithopod from China. Journal of Vertebrate Palaeontology, 
23(supplement to number 3), 68A

And the published abstract is:

SYSTEMATIC REVISION OF "YANDUSAURUS" MULTIDENS, A MIDDLE JURASSIC ORNITHOPOD 
FROM CHINA

KNOLL, Fabien, Muséum des Sciences Naturelles, Orléans, France; BARRETT, Paul 
M.,The Natural History Museum, London, United Kingdom

"Yandusaurus multidens" is an ornithischian from the Lower Shaximiao Formation 
(?Bajocian) of Dashanpu (Sichuan Province, China). The name-bearing type 
(Zigong Dinosaur Museum T6001) is a relatively complete skeleton lacking only 
the rostral extremity of the skull, most of the mandibles, and the caudal 
extremity of the tail. The paratype is constituted by a disarticulated and less 
satisfactorily preserved skeleton.
"Yandusaurus multidens" is recurrently considered to be a junior synonym of Y. 
hongheensis, type-species of the genus, the material of which comes from the 
Upper Shaximiao Formation (? Oxfordian) of Hongheba (Sichuan Province). 
However, significant differences exist between the two species. For example, 
the coracoid of "Y." multidens lacks the ridge on the lateral surface and the 
ventral embayment that are present in Y. hongheensis. In addition, the scapula 
is shorter than the humerus in the former whereas they are equal in length in 
the latter. Maxillary tooth morphology, enamel thickness, and the degree of 
tooth wear also differ. The presence of more teeth in the maxilla of "Y." 
multidens contradicts the hypothesis that this species represents juvenile 
individuals of the larger Y. hongheensis. Consequently, these distinctions 
appear to be sufficient to warrant a generic distinction between these two 
species. Moreover, the validity of Y. hongheensis is currently questionable, 
further destabilising the genus.
"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.