Trilobites as Hosts for Parasites: From Paleopathologies to Etiologies

Extant marine arthropods are afflicted by a variety of parasitic diseases making it plausible that extinct trilobites also had a variety of parasites. Direct evidence in the form of preserved parasite body fossils is lacking to date, which is not surprising considering the poor preservation potential of soft tissues of parasites and their hosts. Some of these interactions might leave traces and pathologies in their exoskeletons, which can be traced in deep time. Knowledge of the parasitic causes of pathologies in modern arthropods such as crustaceans and horseshoe crabs might, therefore, help to better interpret past afflictions and their potential culprits. Our review shows that a variety of structures have been attributed to parasitism—some more confidently than others. The restriction of these structures to particular trilobite lineages might indicate the influence of phylogeny, anatomy, and potential role of ecology (feeding, mode of life) on infestation risks. However, preservation and research biases might also contribute to differences between time intervals and individual trilobite lineages. Other interactions such as epizoa, bioerosion, as well as other structures, which have been confused with parasitic causes are briefly discussed. The culprits of many of these structures remain elusive.