Scientists have for the first time identified a new species of crustacean parasite based on a fossilized feces imprint.

The familiar fossilized remains of ancient animals consist of skeleton bones or their fragments. In this regard, teeth are the most informative, being the hardest elements of the organism that are difficult to destroy. Some scientifically recognized species are known only from such remains, for instance, a newly discovered species of extinct sharks or a venomous lizard with distinctive grooves on its teeth.

Much rarer are other types of traces of ancient life — sometimes literal footprints of dinosaurs, as reported by Naked Science. Few valuable sources can provide insight into the diet of extinct animals: fossilized food found in the stomach or intestines and the end product of digestion — feces, which in fossilized form are called coprolites.

American paleontologists from Kent State University in Ohio and the Calvert Marine Museum in Maryland discovered a unique coprolite specimen, likely left by an ancient fish. The surface of the coprolite bore an imprint of a cymothoid isopod, which typically parasitizes bony fish. According to the experts, this is the first recorded imprint of this arthropod, and the exceptional preservation of the trace allowed the authors to identify a new species and genus of isopod. A detailed description has been published in the journal Palaeontologia Electronica.

Jason Osborn, an American who did not participate in the study, found the coprolite at the bottom of the Pamunkey River in Virginia while swimming. He took the specimen to the Calvert Marine Museum, after which paleontologists began to describe it. For a detailed study of the imprint, specialists created latex casts, as the anatomical features were poorly defined in the natural state.

The size of the specimen — 73 millimeters in length and 22 in width — suggested to researchers that the "author" of the coprolite was a vertebrate. The distinct trace of the exoskeleton of the cymothoid isopod, which usually parasitizes fish, indicates that the fossil could have been produced by a fish, or it could have been swallowed along with the parasite by another creature — a turtle, crocodile, or mammal. Most likely, it was a crocodile, as both the structure, size, and shape resemble previously discovered coprolites of crocodilians.

The deposits in which the coprolite was found date to the lower Miocene of the Neogene period. It was difficult to determine the dating more precisely, but many fossils from the Burdigalian stage were found nearby. In other words, the coprolite is approximately 20 million years old.

Fossilized isopods, as noted by paleontologists, are quite rare, and the imprint of the exoskeleton is an entirely unique find. Representatives of the family Cymothoidae are typically large crustaceans ranging from one to six centimeters in length — the imprinted specimen measures 17 millimeters. Although there is little fossil material to accurately determine the taxonomic affiliation of the parasite, researchers have assigned it to a new genus and species, Calverteca osbornei. The name derives from the Calvert formation where the coprolite was discovered and the name of the American who found the specimen.

Biology recognizes more than ten thousand species of isopods, but as a fossil imprint on a coprolite, it is noted for the first time. Paleontologists also suggested that the lifestyle of these crustaceans in the Miocene may have differed from modern times, and perhaps isopods parasitized not only fish but also reptiles — for example, crocodiles.