Data from: Sexual dimorphism and sexual selection in cytheroidean ostracodes from the Late Cretaceous of the US Coastal Plain

Sexual dimorphism is common in many extant animals, but it is difficult to
demonstrate in fossil species. Working with material from the Late
Cretaceous of the U.S. Coastal Plain, we herein analyze sexual dimorphism
in ostracodes from the superfamily Cytheroidea, a group whose extant
members have males that are relatively more elongate than females. We
digitized outlines of more than 6000 individual ostracode valves or
carapaces, extracted size (area) and shape (length-to-height ratio)
information, and used finite mixture models to assess hypotheses of sexual
dimorphism. Male and female clusters can be discerned in nearly all
populations with sufficient data, resulting in estimates of size and shape
dimorphism for 142 populations across 106 species; an additional nine
samples are interpreted to consist only of females. Dimorphism patterns
varied across taxa, especially for body size: males range from 30% larger
to 20% smaller than females. Magnitudes of sexual dimorphism are generally
stable within species across time and space; we can demonstrate
substantial evolutionary changes in dimorphism in only one species,
Haplocytheridea renfroensis. Several lines of evidence indicate that
patterns of sexual dimorphism in these ostracodes reflect male investment
in reproduction, suggesting that this study system has the potential to
capture variation in sexual selection through the fossil record.