Neanderthals living on the coast of modern-day Italy were diving for shells and utilizing the seas as a resource for tools 100,000 years ago, long before Homo sapiens showed up, a new study reveals.

Though Neanderthals were known to have used sometimes quite complex tools, the extent to which they used coastal resources was less clear. Evidence of shells being turned into scraper tools have been found before now, but a new study published in PLOS ONE has shown that Neanderthals didn’t just collect coastal detritus washed up on beaches, but actively collected marine creatures from the sea by wading and even diving underwater.

Last year a study revealed that the prevalence of swimmer's or surfer’s ear – a bone growth in the ear canal usually associated with habitual exposure to cold water – in Neanderthals suggested they regularly went to the coast to fish. This study adds to the growing evidence that Neanderthals were frequently exploiting underwater resources, long before the arrival of modern humans in Western Europe, who were thought to have introduced this behavior to the region.

Paola Villa of the University of Colorado, Boulder and colleagues looked at artifacts discovered at the Neanderthal archaeological cave site of Grotta dei Moscerini on the west coast of Italy, in between what is now Rome and Naples. It’s one of only two Neanderthal coastal sites where shell tools have been found in Italy.

In 1949, 171 clam shells that had been hand-modified to use as scapers, or knives, the already-sharp edges chipped away at with stone tools to make them sharper, were discovered at this site. They were dated to between 90,000 and 100,000 years old, meaning they were from the Middle Paleolithic. At the time, it wasn’t clear if the shells had been picked up from the beach or sourced from the water.

Villa and colleagues revisited these tools and discovered that nearly a quarter of these clam shells had shiny, smooth exteriors, indicative of being picked up from the seafloor rather than rough, worn, or damaged shells that were more likely picked up from a beach.

Callista chione, the species of clam found, live in water from 1 meter to 200 meters (3-356 feet) down. This, the researchers say, shows Neanderthals likely dived to depths of 1-4 meters (3-12 feet), holding their breath, to pluck the living clams – prized due to their thicker shells – from the seafloor.

They also found an abundance of pumice stones at the site, which likely drifted in the currents from erupting volcanoes like Vesuvius in the Gulf of Naples, 70 kilometers (43 miles) south. These would have been used as abrasive tools to smooth or polish items, much like sandpaper.

These the researchers think probably were plucked from the beach. Their abundance suggests they were a popular tool, and along with the shells – which probably made a tasty meal too – may have been an enticement for Neanderthals to visit the coast.

This evidence adds to the growing picture we have of Neanderthals as a complex people who created art, buried their dead, decorated their bodies with jewelry, cared for the disabled, and had already discovered penicillin. Now we can add capable free divers.