In the 1980s, a Neanderthal cave dwelling was identified on the coast of Portugal, some 20 miles south of Lisbon. Ten years ago, a team of experts revisited the cave, and in one of its tiny nooks, they found a rich cache of remains from aquatic animals like fish, mussels, crustaceans, sharks, dolphins and seals—signs of a seafood smorgasbord.

The discovery, described in a new report in Science, was a remarkable one. Scientists had previously unearthed hints that Neanderthals exploited marine resources; the extinct hominids fashioned tools out of clam shells and used shells to make jewelry beads. But there had been no evidence that Neanderthals were hunting aquatic animals in a significant way. In fact, some experts had posited that the consumption of seafood helped give Homo sapiens an edge over Neanderthals; fish and other marine creatures are rich in omega-3 fatty acids, which promote the development of brain tissue.

Enhanced cognitive development bolstered by seafood could, in theory, explain why early humans were capable of abstract thought and communication—as evidenced by their apparent use of body paint and ornaments, for instance—and why they formed organized, complex societies. But “if [marine foods] were important to modern humans, then they were important for Neanderthals as well—or perhaps they did not have the importance people have been attributing to them,” study co-author João Zilhão of the University of Barcelona, tells the Guardian’s Nicola Davis.

The aquatic remains date between 86,000 and 106,000 years ago and were discovered in a small, cramped room of cave of Figueira Brava.

“I was in the fetal position every single day,” Filipa Rodrigues, an archaeologist at the University of Lisbon who worked on the excavation, says in an interview with Nicholas St. Fleur of the New York Times.

Today, the cave is located right along the coast, but in the days of the Neanderthals, it would have been about a mile away. They seem to have been transporting large quantities of food from the sea. In some areas of the cave, the density of shells was more than 800 pounds per cubic meter, suggesting that they used baskets or bags as part of their fishing process.

Some of the remains—like those belonging to seals, dolphins and waterfowl—may have been scavenged from the shore, but the smaller prey could have been easily plucked from low tides, the researchers say. Their hunting methods may not have been complicated, but the Neanderthals of Figueira Brava seem to have had an understanding of tidal patterns and, possibly, some of the risks associated with seafood consumption; phytoplankton blooms during warmer months can cause shellfish to become toxic.

Traces of horses, deer and pine nuts were also discovered in the cave, which in conjunction with the aquatic animal finds, “reflect the exploitation of all ecosystems present in the site’s catchment among mountain, estuary, and sea: rocky shores, coastal lagoons, alluvial plains, dune pinewoods, and forested slopes,” the study authors write.

But if Neanderthals were capable of extensive marine hunting why, until now, has no evidence of their seafood diet surfaced? It is possible, according to the researchers, that the advance of polar ice caps over a long period of climate change destroyed most coastal deposits that testified to Neanderthals’ exploitation of marine resources. But Figueira Brava is located along a “very steep shelf,” they write, which “has enabled extant and submerged shorelines to be preserved short distances apart.”

The new study provides further evidence that Neanderthals were far more sophisticated than their brutish reputation suggests. Research has shown that they buried their dead, cared for their sick, possibly painted caves. They interacted and mated with early humans—and, according to Zilhão, were likely not all that different from them.

“I feel ... uncomfortable with the comparison between Neanderthals and Homo sapiens, because the bottom line is Neanderthals were Homo sapiens, too,” he tells Davis. “Not only was there extensive inter-breeding … but also in every single aspect of cognition and behaviour for which we have archaeological evidence, Neanderthals pass the sapiens test with outstanding marks.”