Micropachycephalosaurus hongtuyanensis & Wannanosaurus yansiensis

[Tim Williams <twilliams_alpha@hotmail.com>]

Richard J. Butler, Qi Zhao (In Press).  The small-bodied ornithischian 
dinosaurs _Micropachycephalosaurus hongtuyanensis_ and _Wannanosaurus 
yansiensis_ from the Late Cretaceous of China.  Cretaceous Research.  Corrected 
Proof, Available online 8 April 2008 doi:10.1016/j.cretres.2008.03.002    
(Can't pin down the URL.)


Abstract: "The type material of the small-bodied ornithischian dinosaurs 
_Micropachycephalosaurus hongtuyanensis_ and _Wannanosaurus yansiensis_ from 
the Late Cretaceous of China is reviewed.  _Micropachycephalosaurus_, from the 
Wangshi Formation (Campanian) of Shandong Province, was originally referred to 
the clade Pachycephalosauria, but some later authors have considered it a nomen 
dubium.  However, despite the extremely fragmentary nature of the holotype 
specimen, _Micropachycephalosaurus_ can be diagnosed by the presence of 
prominent grooves on the ventral surface of the centra of the posterior dorsal 
vertebra.  Unambiguous pachycephalosaur synapomorphies cannot be identified in 
the currently available material, and we consider this taxon Cerapoda incertae 
sedis.  _Wannanosaurus_, from the Xiaoyan Formation (Campanian-?early 
Maastrichtian) of Anhui Province, can be diagnosed by the extreme flexure of 
the humerus, and is clearly referable to Pachycephalosauria on the basis of a
 large number of synapomorphies.  Assessment of the phylogenetic placement of 
this _Wannanosaurus_ within Pachycephalosauria is complicated by the probable 
juvenile nature of the holotype and paratype specimens."



Anyway, there you have it: _Wannanosaurus_ is a pachycephalosaur, and 
_Micropachycephalosaurus_ *might* be one as well, but positive evidence is 
lacking.  For _Micropachycephalosaurus_ , the accuracy of the name appears to 
be suspect, for more than one reason: the estimated length of 
_Micropachycephalosaurus_ is considerably revised upward (from 50-60 cm to over 
a meter - still fairly runty, but not *that* small); and the thickened skull 
roof, which would probably clinch pachycephalosaurian affinities, could not be 
located among the material.


Cheers

Tim







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