AN ASYNCHRONOUS MESOZOIC MARINE REVOLUTION IN ECHINOIDS

An increase in the frequency of predatory drill hole traces in mollusk prey is the hallmark of the Mesozoic Marine Revolution (MMR), signifying an escalation of biotic interactions associated with the diversification of the Modern Fauna. Quantifying the intensity of biotic interactions by proxy of predation traces is thus crucial for elucidating the tempo and mode of escalation in other important marine invertebrate groups.

Here, we establish temporal trends in the frequency of drill holes of predatory origin recorded in fossilized tests of echinoids, a diverse and ecologically important constituent of the Modern Evolutionary Fauna. A dataset of Meso-Cenozoic drill holes in echinoid populations was compiled to establish temporal trends in echinoid-targeted predatory drilling using museum collections, field work, and literature reports. A total of 263 populations, representing 123 species (34,823 individuals) and spanning 36 chronostratigraphic ages were used for drill-hole frequency tabulation. Sampled populations spanned at least three continents across all time intervals, and represent echinoid populations from North America, Central America/Caribbean, Eurasia, and the Indo-Pacific/Oceania. Both epifaunal regular echinoids and infaunal irregular echinoid taxa were included. We find an intensification of drilling in the Eocene, concurrent with radiation of predatory cassid gastropods. This notably postdates the onset of rapid diversification of infaunal echinoid taxa, thought to be a strategic anti-predatory adaptation, by approximately 100 million years. We show that the intensification of predatory interactions does not necessarily produce a co-evolutionary or escalatory response in prey. The Eocene intensification of drilling predation on echinoids also significantly postdates the Cretaceous onset of intense mollusk-targeting drilling, suggesting that the MMR was asynchronous across marine invertebrate taxa, and induced several uncoordinated steps that varied across predator-prey groups.