There’s nothing especially remarkable about archaeologists studying stone tools and shell middens—unless they weren’t made by humans. A new study suggests that sea otters create a distinct archaeological record, and it might eventually have a lot to tell us about their evolutionary history.

Sea otters are ingenious—and adorable—tool users. They often pick up small rocks and use them to crack open snails, clams, or mussels; underwater, otters also use rocks to pry abalone loose from the seafloor. Closer to shore, otters whack mussels against protruding boulders until they damage the bivalves’ hinges enough to pry them open. That percussive food preparation leaves behind a unique signature: distinctive marks on the boulder and a pile of broken mussel shells, most cracked in a particular way, piled at the bottom.

“Sea otters have created a distinct, recognizable archaeological record,” wrote Michael Haslam and his colleagues, who claim that by doing a little mustelid marine archaeology, ecologists could track past habitats of sea otter populations and maybe even the evolution and spread of otter tool use.