Data from: Recognizing sexual dimorphism in the fossil record: lessons from nonavian dinosaurs

The demonstration of sexual dimorphism in the fossil record can provide
vital information about the role that sexual selection has played in the
evolution of life. However, statistically robust inferences of sexual
dimorphism in fossil organisms are exceedingly difficult to establish,
owing to issues of sample size, experimental control, and methodology.
This is particularly so in the case of dinosaurs, for which sexual
dimorphism has been posited in many species, yet quantifiable data are
often lacking. This study presents the first statistical investigation of
sexual dimorphism across Dinosauria. It revisits prior analyses that
purport to find quantitative evidence for sexual dimorphism in nine
dinosaur species. After the available morphological data were subjected to
a suite of statistical tests (normality and unimodality tests and mixture
modeling), no evidence for sexual dimorphism was found in any of the
examined taxa, contrary to conventional wisdom. This is not to say that
dinosaurs were not sexually dimorphic (phylogenetic inference suggests
they may well have been), only that the available evidence precludes its
detection. A priori knowledge of the sexes would greatly facilitate the
assessment of sexual dimorphism in the fossil record, and it is suggested
that unambiguous indicators of sex (e.g., presence of eggs, embryos,
medullary bone) be used to this end.