Parasites Found in 200-Million-Year-Old Fossilized Feces

Fossilized feces preserve evidence of ancient parasites that infected an aquatic predator over 200 million years ago, according to a study published August 9, 2023 in the open-access journal PLOS ONE by Thanit Nonsrirach of Mahasarakham University, Thailand and colleagues.

Parasites are a common and important component of ecosystems, but ancient parasites are difficult to study due to a poor fossil record. Parasites often inhabit the soft tissues of their host, which rarely preserve as fossils. There are, however, cases where traces of parasites can be identified within fossilized feces (coprolites). In this study, Nonsrirach and colleagues describe evidence of parasites in a Late Triassic coprolite from the Huai Hin Lat Formation of Thailand, which is over 200 million years old.

The coprolite is cylindrical in shape and over 7cm long. Based on its shape and contents, the researchers suggest it was likely produced by some species of phytosaur, crocodile-like predators which are also known from this fossil locality. Microscopic analysis of thin sections of the coprolite revealed six small, round, organic structures between 50-150 micrometers long. One of these, an oval-shaped structure with a thick shell, is identified as the egg of a parasitic nematode worm, while the others appear to represent additional worm eggs or protozoan cysts of unclear identity.

This is the first record of parasites in a terrestrial vertebrate host from the Late Triassic of Asia, and a rare glimpse into the life of an ancient animal that was apparently infected by multiple parasitic species. This discovery also adds to the few known examples of nematode eggs preserved within the coprolites of Mesozoic animals. These findings are therefore a significant contribution to scientific understanding of the distribution and ecology of parasites of the distant past.

The authors add: "Coprolite is a significant paleontological treasure trove, containing several undiscovered fossils and expanding our understanding of ancient ecosystems and food chains."