DOI: 10.5061/dryad.qs7ks
title: Data from: Sexual dimorphism and sexual selection in cytheroidean ostracodes from the Late Cretaceous of the US Coastal Plain

description: 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.
description: Table
 S1Dimorphism estimates and
 information about analyzed populations. Status indicates whether
 reasonable dimorphism estimates could be obtained ("OK") or why
 they could not be found. ∆BIC is the difference in support between the
 best one- (BIC1) and two-group (BIC2) models, with positive values
 indicating greater support for the two-group model. CovStruct refers to
 the assumptions of the best supported model about how variance/covariance
 patterns are similar across sexes (see Table 1); CovStruct Selection
 indicates whether the CovStruct assumption was the best supported among
 all those implemented in Mclust ("best model") or if only a
 subset of models were considered ("imposed", with "imposed
 E_I" indicating that only models EEI, EVI, and EII were allowed).
 Combining data left and right valves requires specifying a method for this
 offset (LR offset method); see text for details. Dimorphism, female area
 and female L/H data were all natural-log transformed.Figure
 S1Methods used to
 determine the offset between left and right valve data, illustrated with
 the population HAP_NANI-1. (A) Original data, before any offset is
 applied. As is typical for many cytheroids, right valves are smaller and
 more elongate than left valves. Note also that the sex ratios appear to
 differ between the sexes: most right valves are from the larger, male
 cluster, whereas the majority of left valves are females. This shifts the
 mean of right valves towards that of males, and the mean of left valves
 towards that of females. When valve means are used to determine left-right
 offsets (B), right valves are now systematically smaller and less elongate
 because the skewed sex ratios have resulted in an overcorrection for right
 valves away from male-like values. In contrast, fitting the mixture model
 while allowing left-right offsets to be freely optimized (C) provides a
 much better overlay of left and right valve data.HuntetalFigureS1.epsFigure S2Shape dimorphism plotted against female body size (log[area], left panel) and female shape (log[length/height], right panel). Solid black lines are lowess regressions.HuntetalFigureS2.eps