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Torosaurus found to be distinct from Triceratops



From: Ben Creisler
bcreisler@gmail.com


New in PLoS ONE:


Leonardo Maiorino, Andrew A. Farke, Tassos Kotsakis & Paolo Piras (2013)
Is Torosaurus Triceratops? Geometric Morphometric Evidence of Late
Maastrichtian Ceratopsid Dinosaurs.
PLoS ONE 8(11): e81608.
doi:10.1371/journal.pone.0081608
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0081608


Background

Recent assessments of morphological changes in the frill during
ontogeny hypothesized that the late Maastrichtian horned dinosaur
Torosaurus represents the “old adult” of Triceratops, although
acceptance of this finding has been disputed on several lines of
evidence.

Methodology/Principal Findings

Examining the cranial morphology of 28 skulls in lateral view and 36
squamosals of Nedoceratops hatcheri, Triceratops spp. and Torosaurus
spp. by means of landmark-based geometric morphometrics, we compared
ontogenetic trajectories among these taxa. Principal Component
Analysis and cluster analysis confirmed different cranial
morphologies. Torosaurus shape space is well separated from
Triceratops, whereas Triceratops horridus and Triceratops prorsus
partially overlap within Triceratops shape space. Linear regressions
between shape and size suggest different ontogenetic trajectories
among these taxa. Results support the “traditional” taxonomic status
of Torosaurus. We hypothesize that ontogeny drives cranial morphology
with different patterns between Torosaurus and Triceratops.

Conclusions/Significance

Torosaurus is a distinct and valid taxon. Whether looking at entire
skulls, skulls without the frill, frills alone, or squamosals,
Torosaurus has different morphologies and distinct allometric
trajectories compared to Triceratops. This new approach confirms the
taxonomic status of Torosaurus as well as the comparatively low
diversity of ceratopsids at the end of the Maastrichtian in North
America.