Data from: Standardising fossil disparity metrics using sample coverage

Estimating past biodiversity using the fossil record is a central goal of
palaeobiology. Because raw estimates of biodiversity are biased by
variation in sampling intensity across time, space, environments, and
taxonomic groups, sampling standardisation is routinely applied when
estimating taxonomic diversity (e.g., species richness). However, sampling
standardisation is less commonly used when estimating alternative
currencies of biological diversity, such as morphological disparity. Here,
we show the effects of standardising fossil time series of morphological
disparity to equal sample completeness, or “coverage” of the underlying
taxon-frequency distribution. We apply coverage-based standardisation to
three published datasets of discrete morphological characters
(echinoderms, ichthyosaurs, and ornithischian dinosaurs), and quantify
disparity using two metrics: weighted mean pairwise dissimilarity (WMPD)
and the sum of variance (SOV). We also compare the effects of
coverage-based and sample-size-based standardisation. Our results show
that coverage standardisation can yield estimates of disparity through
time that dramatically deviate from raw estimates, both in magnitude and
direction of changes. These findings demonstrate that future studies of
morphological disparity should control for variation in sampling intensity
to make more reliable inferences.