SAMPLING BIASES IN THE RISE AND FALL OF FOSSIL MARINE ANIMAL GENERA

An important question in evolutionary biology and macroecology is whether taxa show systematic trajectories in geographic range size and occupancy over macroevolutionary timescales. Past studies have used the fossil record to document these trajectories, showing various patterns, among which being symmetric rise and falls. In this study, I focus on several biases in the record that have been unaccounted for in past analyses of occupancy trajectories. First, I show that more complete sampling in the first and last time bins of a taxon’s stratigraphic range results in lower occupancy in those bins. This could result in an abrupt rise and fall of occupancy even when the underlying trajectory is more gradual. I show through simulations that conditioning these boundary bins to be sampled in the same way as intermediate bins will eliminate this bias. Second, the possibility that taxa may have incomplete durations within boundary bins could also lower occupancy in those bins. As such, I examine how using taxa that have been constrained to exist throughout entire intervals at the substage level impact empirical occupancy trajectories. Considering these factors, the occupancy trajectories of marine animal genera look to be a relatively quick rise after origination. This is followed by a short-term stable level before a gradual decline towards extinction.