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No sexual dimorphism in Protoceratops

Ben Creisler

New in PLoS ONE:

Leonardo Maiorino, Andrew A. Farke, Tassos Kotsakis & Paolo Piras (2015)
Males Resemble Females: Re-Evaluating Sexual Dimorphism in
Protoceratops andrewsi (Neoceratopsia, Protoceratopsidae).
PLoS ONE 10(5): e0126464


Protoceratops andrewsi (Neoceratopsia, Protoceratopsidae) is a
well-known dinosaur from the Upper Cretaceous of Mongolia. Some
previous workers hypothesized sexual dimorphism in the cranial shape
of this taxon, using qualitative and quantitative observations. In
particular, width and height of the frill as well as the development
of a nasal horn have been hypothesized as potentially sexually

Methodology/Principal Findings

Here, we reassess potential sexual dimorphism in skulls of
Protoceratops andrewsi by applying two-dimensional geometric
morphometrics to 29 skulls in lateral and dorsal views. Principal
Component Analyses and nonparametric MANOVAs recover no clear
separation between hypothetical “males” and “females” within the
overall morphospace. Males and females thus possess similar overall
cranial morphologies. No differences in size between “males” and
“females” are recovered using nonparametric ANOVAs.


Sexual dimorphism within Protoceratops andrewsi is not strongly
supported by our results, as previously proposed by several authors.
Anatomical traits such as height and width of the frill, and skull
size thus may not be sexually dimorphic. Based on PCA for a data set
focusing on the rostrum and associated ANOVA results, nasal horn
height is the only feature with potential dimorphism. As a whole, most
purported dimorphic variation is probably primarily the result of
ontogenetic cranial shape changes as well as intraspecific cranial
variation independent of sex.