What you see here are coprolites—a fancy name for fossilized poops, which allows paleontologists to seriously discuss something that could otherwise end up eliciting a lot of immature giggles. Notice, if you will, the giant teeth marks in the coprolite on the left. Those were likely made by either a Physogaleus or a Galeocerdo, ancient, extinct sharks related to the modern Tiger Shark.
And, while it's pretty awesome that paleontologists can match tooth marks well enough to fossil anatomy to narrow the biter down to one of two species, the real thing we all want to know is, "Why the heck was a shark biting poop?"
Tiger Sharks have not been documented as poop-eaters. Plus, if the ancient sharks were trying to eat poop, you'd think they'd have succeeded. Instead, we have coporolites—un-eaten, but still bitten. It's a mystery. But, according to science blogger Brian Switek, researchers from Maryland's Calvert Marine Museum and the American Institutes for Research, have a theory. An awesome theory.
The pattern of the bite marks and the fact that the feces were not ingested is consistent with a reconstruction in which, during an attack on another animal, the shark either bit through the body wall and guts to leave the tooth impressions or bit the intestines after disemboweling its prey. Such an attack would have left tooth marks on the feces, which probably fell out of the intestine shortly afterward, hence "In this scenario, the shark chose not to eat the feces, which drifted away, settled out of sight, or otherwise avoided attention."
Brian Switek: Unique fossils record the dining habits of ancient sharks
Image from "Shark-bitten vertebrate coprolites from the Miocene of Maryland" in the journal Naturwissenschaften