PHANEROZOIC TRENDS IN PARASITE-HOST INTERACTIONS AMONG COMMON MARINE BENTHOS: MOUNTING RISK OR SPURIOUS CONSEQUENCE OF A BIASED RECORD?

Most living parasitic taxa are small and non-mineralized, which might suggest the difficulty of quantifying parasite-host interactions in deep time. However, this assumption incorrectly discounts the rich trace fossil record of malformations induced by parasites on host skeletons. Similar to the drill hole record of predation, parasite-induced malformations, though limited in taxonomic scope, are among the most abundant direct evidence for such biotic interactions in the fossil record. We have compiled a database of traces and biotic associations attributed to parasitism in order to better understand the Phanerozoic history of parasite-host interactions among benthic marine invertebrates. The data comprise 1,014 species occurrence level observations from the published literature that range in age from Cambrian to Recent. We recorded the original authors’ interpretations of the biotic interactions (i.e., parasitism, predation, or mutualism) and then further refined these interpretations. This resulted in 653 species occurrences of known geologic age that we consider to be parasite-host interactions. Here we analyze temporal trends in parasite prevalence values for four common benthic marine invertebrate host taxa (brachiopods, crinoids, bivalves, and echinoids; n=254) from samples with n >/= 10 (n=172). Parasite prevalence was generally low (< 0.2) in the middle to late Paleozoic, with the exception of the Mississippian Period (~0.4). There is a dearth of occurrence and prevalence data from the Pennsylvanian through Triassic periods despite systematic searches. Prevalence values monotonically increased from the Jurassic (~<0.1) through Neogene (~0.5). These results are broadly similar to the Phanerozoic histories of predation intensity among marine invertebrates (Huntley and Kowalewski, 2007), Sepkoski’s marine genus diversity (Sepkoski, 2002), and various estimates of rock availability and sampling through the Phanerozoic. Taphonomic and sampling biases likely exerted a first order, Phanerozoic scale control on sample availability. However, estimates of parasite prevalence are based on proportional data and are likely less influenced by such biases. The long term increase in parasite prevalence is further evidence for increasingly hazardous benthic marine ecosystems through time.