Data from: Onshore-offshore gradient in metacommunity turnover emerges only over macroevolutionary time scales

Due to higher variability in population sizes, extinction rates, and origination rates, invertebrate lineages tend to turn over at a higher rate in onshore than in offshore habitats over long temporal durations (>10 Myr), but it remains unclear whether this pattern scales down to durations of stages (<5 Myr) or even sequences (<0.5 Myr). We assess whether onshore-offshore gradients in long-term turnover between the tropical Eocene and the warm-temperate Plio-Pleistocene can be extrapolated from gradients in short-term turnover, using abundances of molluscan species from bulk samples in the NE Atlantic Province. Temporal turnover of metacommunities does not significantly decline with depth over short durations (<5 Myr), but significantly declines with depth between the Eocene and Plio-Pleistocene (~50 Myr). This decline is determined by a higher onshore extinction of Eocene genera and families, by a higher onshore variability in abundances of genera and families, and by an onshore expansion of genera and families that were frequent offshore in the Eocene. Onshore-offshore decline in turnover thus emerges over long temporal durations. Plio-Pleistocene metacommunities show a high proportion of bathymetric generalists, in contrast to Eocene metacommunities. Accordingly, the net cooling and weaker thermal gradients may have allowed offshore specialists to expand into onshore habitats and maintain their presence in offshore habitats.