Data from: Fecundity in fossil Bryozoa: Accounting for colony fragmentation and the spatial division of reproductive labor

Our ability to measure evolution by natural selection in the fossil record
is limited by the near impossibility of estimating the fecundity and thus
relative fitness of most fossil organisms. Neocheilostome bryozoans are an
important exception, because they have calcified larval brood chambers
known as ovicells that provide an approximate estimate of the colony’s
sexual fecundity. This clade has a rich fossil record dating back ~100
million years, providing potential opportunities to observe changes in
relative fitness and natural selection through many past intervals of
environmental change. However, neocheilostome fossil specimens are often
highly fragmented, and fragments are not necessarily randomized subsets of
a colony. To make use of the majority of the neocheilostome fossil record,
we need to test the effect colony organization has on our methods of
inferring colony fecundity from fragmented specimens. In this study, we
measure colony fecundity in a population of Recent neocheilostome bryozoan
specimens of the species Parasmittina eccentrica Winston &
Jackson, 2021, and quantify the nonrandom spatial arrangement of
ovicells due to colony organization. We then simulate fragmenting these
specimens and test the statistical robustness of standard methods one
might use to reconstruct fecundity from fossil specimens. We find that
ovicells are clustered and concentrated at mid-distances from the
ancestrula (the oldest part of the colony). As a result, estimates of a
colony’s fecundity from a single fragment have higher variance than would
be expected if ovicells were randomly distributed. When estimating average
population fecundity, observed variance among fossil fragments is a better
estimator of sample variance than methods that assume spatial independence
(such as a binomial distribution), especially for fragment sizes of 8 mm
or less. While there is much to be learned about neocheilostome ovicell
arrangement across taxa and environments, we can robustly estimate
fecundity from small fossil fragments even in extinct neocheilostome
species.