One day, 5 to 20 million years ago, a tongue-eating isopod parasitized some unknown Miocene fish, embedding itself in the fish’s mouth where wit would grow and consume scraps as its host feed. That partnership lasted until the fish, itself, became food, likely eaten by an ancestral sea turtle.
And that’s where a million-year old story should end. But in 2023, a diver surveying the bed of the Pamunkey River in Virginia came across a coprolite, the fossilized feces of a long dead animal. And within that coprolite, perfectly preserved in negative, was a near-perfect impression of that tongue-eating isopod.
To give you an idea of just how rare this discovery is, impressions of organisms preserved in coprolites have been found exactly two other times. A fragment of a sea turtle hatchling’s shell was found in 2017. An ammonite impression was found in a coprolite in 2022. Not other arthropod and no other isopod has ever been found preserved in fossil feces.
Cymothoid isopods are still extremely common throughout the world. They gained notoriety as the tongue-eating isopod from viral images of sinister sea creatures clinging to the inside the fish mouths. You might also find them clinging to the flesh of fish or in their gills or eyes. Buccal-dwelling cymothoids do destroy the tongue when they parasitize their host, replacing the organ with their own body. The fish almost certainly are not thrilled with this turn of events.
This particular cymothoid isopod was so well preserved that the researchers were able to describe the species. They named it Calverteca osbornei and it is now housed at the Calvert Marine Museum in Solomons Island, Maryland. While the story above is a reasonable hypothesis for how the isopod came to leave an impression in fossilized feces, the authors note that they do not know whether the isopod itself was consumed and excreted or if the isopod and potential fish host were consumed by other large common predators, like sea turtles, crocodiles, or marine mammals.
The body impression of a new genus and species of cymothoid isopod (Cymothoidae, Crustacea) preserved in a vertebrate coprolite from the Atlantic Coastal Plain (Miocene, Chesapeake Group) of Virginia, USA by Stephen J. Godfrey, Rodney M. Feldmann, and Carrie E. Schweitzer is available Open-Access in the journal Paleaontologia Electronica: https://palaeo-electronica.org/content/2024/5363-isopod-impression-in-a-coprolite
Feature Image: FIGURE 2. CMM-V-11695, a Miocene vertebrate coprolite preserving an impression of the dorsal surface of a cymothoid isopod, Calverteca osbornei gen. et sp. nov. A. View of the length of the coprolite and the body impression of the cymothoid isopod. B. Enlarged view of the end of the coprolite and the isopod body impression. The anterior end of the isopod is oriented upward. The coprolite was dusted with sublimed ammonium chloride to highlight detail and improve contrast. White scale bars equal 10 mm. From The body impression of a new genus and species of cymothoid isopod (Cymothoidae, Crustacea) preserved in a vertebrate coprolite from the Atlantic Coastal Plain (Miocene, Chesapeake Group) of Virginia, USA.
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