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Clade
Subclade Archosauria: Avemetatarsalia to Neornithes 

Taxon Feedback
Taxon Hypsilophodontidae 
Nominal Author Dollo 1882 
2° Nominal Author  
Taxon Status active
inactive
Comments This clade has been recognized for some time as a monophyletic assemblage of basal ornithopods, although united by only a few synapomorphies (Sereno 1986). Some recent cladistic analyses, in contrast, have challenged hypsilophodontid monophyly (e.g. Winkler et al. 1998, Weishampel et al. 2003). Norman et al. (2004), for example, found traditional hypsilophodontids to represent a paraphyletic grade basal to Iguanodontia. The name is probably best defined as it is here, to include any taxxa most closely related to the nominotypical genus Hypsilophodon, however that may sort out in future analyses.
 
Potential Synonomy  

Active Phylogenetic Definition Feedback
Active Definition The most inclusive clade containing Hypsilophodon foxii Huxley 1869 but not Parasaurolophus walkeri Parks 1922. 
Shorthand > Hypsilophodon foxii but not Parasaurolophus walkeri
Definitional Author Sereno 2005 
Definition Status original
textual substitution
first-order revision
second-order revision
Definition Type node
stem
Node-Stem Triplet yes
no
Other Triplet Taxa  
Specifiers
Specifier A Hypsilophodon foxii 
Specifier(s) B  
Specifier(s) C Parasaurolophus walkeri 
Qualifiers
+Taxon  
-Taxon  
Datum  
Taxonomic Content stem (entirely extinct)
crown (extant-bounded)
mixed (extant/extinct-bounded)
Publication Year 1998 

Inactive Taxon Status Feedback
Rejection Criteria junior synonym
historically polyphyletic
incomplete definition
no definition
apomorphy-based
redundant
other 
Critique  
 

Current Age Range Feedback
Earliest Record Bathoniaan-Callovian (165 Ma) 
Latest Record Maastrichtian (66 Ma) 
Range (My) 99 
Basis for Range The earliest record is based on Yandusaurus hongheensis from the Bathonian-Callovian-age Lower Shaximiao Formation in China. The latest records are several genera from Maastrichtian-age formations in western North America. Dates are rounded to the nearest million, the earliest from the beginning of the stage and the latest from the end of the stage (Gradstein et al. 2004). 

Definitional History #1
Definition 1 All euornithopods closer to Hypsilophodon than to Parasaurolophus
Author Sereno 1998:61 
Type node  stem 
Specifiers Hypsilophodon, Parasaurolophus 
Qualifiers