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CENTROSAUR ONTOGENY PAPER
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"