Discussion

Unravelling the evolutionary history of parasites and parasitism relies predominantly on inferred patterns of host-parasite association through time. Parasite phylogenies that link extant taxa and their ecologies (host association, mode of transmission, life cycle, biogeography) are used to suggest ancestral relatedness, host-switching events and major evolutionary transitions associated with parasitism. However, a reliance on extant host and parasite diversity to infer the past has its limitations: host-switching is common, host range is often poorly understood, and extinct taxa (both hosts and parasites) are neglected. Best estimates of historical events requires an interdisciplinary approach. Direct or inferred evidence of past host-parasite associations in the fossil record are rare but provide means by which phylogenetically-derived hypotheses can be tested and time-calibrated. Fossil evidence of direct host-parasite associations, pathologies and traces may be worthy of further investigation; a mixture of serendipity, awareness and strategic investigation is required. Modern visualisation tools, as applied to fossil material, and a palaeobiological perspective provide new insights into parasite evolution, whilst increasingly robust host and parasite phylogenies yield new opportunities for inferring the evolutionary history of parasitism. In combination, these approaches provide a framework for further hypothesis generation and testing. Here I review recent advances in palaeoparasitology and phylogenetics and suggest opportunities to further explain the present diversity and diversification of parasite lineages by combining these fields.