Paleontologists have stumbled across a scientific first that's sure to inspire both fascination and disgust: coprolites, or fossilized fecal matter, bearing the distinct impressions of a creature's teeth.

The coprolites – one chunk of rock is fist-sized, the other is about 30 percent larger – were discovered on a beach along the western shore of Chesapeake Bay, says Stephen Godfrey, a paleontologist at the Calvert Marine Museum in Solomons, Md.

The impressions in the coprolites are as much as 6.5 millimeters (just over a quarter of an inch) deep, Godfrey and a colleague report online March 9 in Naturwissenschaften. A silicone rubber mold of the tooth marks indicates that the biter was most likely a close relative of today’s tiger shark.

This fossilized poop doesn’t include visible bits of bone, feather or fish scales like similar coprolites unearthed from 15-million-year-old rocks in the nearby cliffs. But the hunks do have a phosphate-rich composition that hints the fecal matter came from a creature that had fed on bony prey. This, along with the size of the coprolites, suggests they came from a large animal, possibly a crocodilian, Godfrey says.

Although sharks are known to taste-test possible prey, Godfrey thinks it’s unlikely that the shark just took a nip of poop floating by to test its palatability. For one thing, he says, the tooth impressions are much deeper on one side of each coprolite than on the other – a scenario that’s unlikely if the delicate fecal matter had been free-floating.

Instead, the researchers contend, the disparity in the depth of the impressions probably resulted because the fecal matter was still inside the shark's prey, or constrained within disemboweled intestines, when bitten.

Images: Stephen Godfrey.