How an Ancient Fish’s Skull Got Filled With Fossilized Feces

It’s the first time a vertebrate’s braincase has ever been found full of coprolites, scientists say.

It’s a dubious distinction in the fossil record: For the first time, a vertebrate has been found with fecal pellets where it’s brain once was.

The fossilized animal was Astroscopus countermani, an extinct fish first described as a separate species in 2011 in Maryland. Also known as a stargazer because its eyes were on top of its head, it was the earliest known member of its family and its genus, which still hunts prey on seafloors all over the world. But approximately 7.5 million to 10.5 million years ago in the Miocene era, scientists suspect this stargazer specimen, which may have been the size of today’s trout, died and its braincase might have been infiltrated by polychaetes or another kind of annelid worm. The creatures may have scavenged the dead fish’s brain, leaving a profuse amount of excrement in their wake.

“This,” said Stephen J. Godfrey, curator of paleontology at the Calvert Marine Museum in Maryland and an author of the study, “was an overachieving worm or worms that burrowed into this little fish!”