The primary sources of paleoparasitological material include mummified tissues, coprolites (fossilised dung) from mammals or dinosaurs, fossils, and amber inclusions. Hair, skins, and feathers also yield ectoparasite remains. Some archaeological artifacts document the presence of animal parasites. One example is the depiction of what appear to be mites in the ear of a "hyaena-like" animal in a tomb painting from ancient Thebes.
Some parasites leave marks or traces (ichnofossils) on host remains, which persist in the fossil record in the absence of structural remains of the parasite. Parasitic ichnofossils include plant remains which exhibit characteristic signs of parasitic insect infestation, such as galls or leaf mines and certain anomalies seen in invertebrate endoskeletal remains.
Plant and animal parasites have been found in samples from a broad spectrum of geological periods, including the Holocene (samples over 10,000 years old), Pleistocene (over 550,000 years old), Eocene (over 44 million years old), Cretaceous (over 100 million years) and even Lower Cambrian (over 500 million years).
One of the most daunting tasks involved in studying parasitic relationships from the past is supporting the assertion that the relationship between two organisms is indeed parasitic. Organisms living in "close association" with each other may exhibit one of several different types of trophic relationships, such as parasitism, mutualism, and commensalism. Demonstration of true parasitism between existing species typically involves observing the harmful effects of parasites on a presumed host. Experimental infection of the presumed host, followed by recovery of viable parasites from that host also supports any claim of true parasitism. Obviously such experiments are not possible with specimens of extinct organisms found in paleontological contexts.
Assumptions of true parasitism in paleontological settings which are based on analogy to known present-day parasitic relationships may not be valid, due to host-specificity. For example, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense are both devastating human parasites, but the related subspecies Trypanosoma brucei brucei will infect a number of animal hosts, but cannot even survive in the human blood stream, much less reproduce and infect a human host. So a related (or unidentifiable) species of Trypanosoma found in a paleontological or archaeological context may not be a true human parasite, even though it appears identical (or very similar) to the modern parasitic forms.