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Nedoceratops as growth stage between Triceratops and "Torosaurus"

From: Ben Creisler

New in PLoS ONE:
Scannella, J.B. & Horner, J.R. (2011)
‘Nedoceratops’: An Example of a Transitional Morphology.
PLoS ONE 6(12): e28705. 
The holotype and only specimen of the chasmosaurine ceratopsid dinosaur 
‘Nedoceratops hatcheri’ has been the source of considerable taxonomic debate 
since its initial description. At times it has been referred to its own genus 
while at others it has been considered synonymous with the contemporaneous 
chasmosaurine Triceratops. Most recently, the debate has focused on whether the 
specimen represents an intermediate ontogenetic stage between typical young 
adult Triceratops and the proposed mature morphology, which was previously 
considered to represent a distinct genus, ‘Torosaurus’.
Methodology/Principal Findings
The only specimen of ‘Nedoceratops hatcheri’ was examined and the proposed 
diagnostic features of this taxon were compared with other chasmosaurine 
ceratopsids. Every suggested autapomorphy of ‘Nedoceratops’ is found in 
specimens of Triceratops. In this study, Triceratops includes the adult 
‘Torosaurus’ morphology. The small parietal fenestra and elongate squamosals of 
Nedoceratops are consistent with a transition from a short, solid 
parietal-squamosal frill to an expanded, fenestrated condition. Objections to 
this hypothesis regarding the number of epiossifications of the frill and 
alternations of bone surface texture were explored through a combination of 
comparative osteology and osteohistology. The synonymy of the three taxa was 
further supported by these investigations.
The Triceratops, ‘Torosaurus’, and ‘Nedoceratops’ morphologies represent 
ontogenetic variation within a single genus of chasmosaurine: Triceratops. This 
study highlights how interpretations of dinosaur paleobiology, biodiversity, 
and systematics may be affected by ascribing o
mic significance.