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As I revealed yesterday, this long awaited paper is now out..

SAMPSON, S.D., RYAN, M.J.  and TANKE, D.H. 1997. Craniofacial 
ontogeny in centrosaurine dinosaurs (Ornithischia: Ceratopsidae): 
taxonomic and behavioural implications. _Zoological Journal of the 
Linnean Society_ 121: 293-337.


Centrosaurine ceratopsians are characterised by well developed nasal 
horncores or bosses, relatively abbreviated supraorbital horncores or 
bosses, and adorned parietosquamosal frills. Recent study of several 
paucispecific (low diversity) bonebed assemblages in Alberta and 
Montana has contributed greatly to out understanding of ontogenetic 
and taxonomic variation in the skulls of centrosaurines. Relative age 
determination of centrosaurines is now possible through examination 
of ontogenetic change in several characters, including surface bone 
morphology of specific skeletal elements. The within-group taxonomy 
of centrosaurines is based almost entirely on characters of the skull 
roof, relating particularly to horns and frills. Juvenile and 
sub-adult centrosaurines are characterized by relatively simple, 
unadorned frills compared to their adult counterparts. As in numerous 
living taxa, the cranial ornaments of centrosaurines developed late 
in ontogeny, as individuals approached or attained adult size. An 
important impliction arising directly from this study is that 
juvenile and sub-adult centrosaurines are difficult to distinguish 
taxonomically at the specific level. Two monospecific genera 
represented only by immature materials, _Brachyceratops montanensis_ 
and _Monoclonius crassus_, cannot be defended and should be 
considered _nomina dubia_. The late ontogenetic development and 
diverse taxonomic variation of horn and frill morphologies support 
the contention that these structures are best interpreted as 
reproductive characters employed in mate competition.


There is stacks of information in this paper, and I cannot do it 
justice in a brief summary. However, I note that Sampson, Ryan and 
Tanke reconstruct the skull of _Centrosaurus apertus_ with those odd 
marginal processes growing across *both* parietal fenestrae. They 
also talk of an undescribed species of _Pachyrhinosaurus_ from 
Alberta's Wapiti Formation bonebed - '_Pachyrhinosaurus_ species' in 
their cladogram (p. 330) - which has 'from one to three spikes on the 
parietal midline bar'. 

If you like horned dinosaurs, this paper is a must.

"I've got too much energy to switch off my mind, but not enough to 
get myself organised"