PATHOLOGIES IN PALEOZOIC TRILOBITES

Trilobites of Paleozoic age provide some of the earliest and most dramatic documentation of malformations known from the fossil record. Although once commonly treated as monstrosities or curiosities, advances in identification reveal specimens showing a history of trauma, disease, parasitism, and infection. Such interpretation provides valuable glimpses into the paleoecology and evolutionary history of trilobites. Accidents, especially those incurred in molting, sublethal predation, and teratological conditions account for a large percentage of malformed specimens. Trilobites retain a record of their wounds, and clues to the processes of wound response and tissue regeneration, in their biomineralized exoskeleton; this helps to distinguish pathological conditions from congenetic malformations. Wound response or other tissue response is key to distinguishing conditions that took place during life from post-mortem events such as scavenging, boring of exoskeletal sclerites, and attachment of larvae to sclerites. A high incidence of healed predation scars in Cambrian trilobites is consistent with the interpretation that predator-prey interactions were an important evolutionary driving force during the Cambrian radiation. Atrophy expressed on some trilobite exoskeletons suggests an origin with infection or parasites. Neoplasms, or nodular growths, on trilobite exoskeletons can sometimes be distinguished as healed, or encased, borings into the exoskeleton, thus recording interactions with microscopic parasites. Other nodular growths resemble tumors, and putatively provide some of the earliest documentation of uncontrolled cellular growth, or cancer, known from fossils.