Neanderthals are often portrayed chowing down on mammoth meals and woolly rhino ribs. But an analysis of their leftovers from a coastal cave in Portugal suggests fish and mollusks claimed a special place on their Paleolithic palates.

“We all have that image of the primitive Neanderthal that eats lots of meat,” said Filipa Rodrigues, an archaeologist at the University of Lisbon and author of a paper published Thursday in Science. “Now, we have this new perspective that they explored the marine resources like Homo sapiens did.”

Archaeologists have previously found evidence that Neanderthals ate, collected and wore jewelry fashioned from shellfish. But evidence they consumed large amounts of fish has been lacking. Some scientists have argued Neanderthals did not have the skill or wit to catch fish as their Homo sapiens contemporaries did in Africa, and may have lost out on consuming aquatic animals rich in fatty acids that could have aided with brain development.

But deep in Cueva de Figueira Brava, which housed Neanderthals about 100,000 years ago, Dr. Rodrigues and her colleagues have uncovered more than 560 fish bones, as well as remains from clams, mussels, crabs, waterfowl, seabirds, seals and dolphins. The findings suggest Neanderthals cast a wide net to add sea creatures to their dinner menus, and the researchers say it shows the behavior of the archaic species was comparable to modern humans that lived at the time.

“In this one tiny window of visibility, they demonstrate that Neanderthals ate quantities of seafood,” said Peter Rowley-Conwy, an archaeologist from Durham University, who was not involved in the study.

When Neanderthals occupied Figueira Brava, it was about a mile from the water. Today the cave, some 20 miles south of Lisbon, is right on the coast. The site had been previously explored and identified in the 1980s as a Neanderthal shelter, but no fish remains were uncovered.

Dr. Rodrigues and her team excavated the cave from 2010 through 2013. To get to their point of interest, they went through one of three cave entrances into a room and then squeezed through a narrow passageway into another, much smaller room. To fit through the channel, Dr. Rodrigues had to stretch one arm straight above her head and place the other at her side and start “crawling like a worm.”

Credit…Zilhão et al. Science, 2020
Credit…Zilhão et al. Science, 2020

Her cramped and damp destination offered little relief.

“I was in the fetal position every single day,” Dr. Rodrigues said. “It’s not possible to stand up or stretch your legs.”

Inside, she worked alongside João Zilhão, an archaeologist from the University of Barcelona and lead author of the study, scraping away and collecting sediments. The two were sometimes joined by a third researcher, but never a fourth because the space was too tight. They had widened an existing hole in the cave wall that led outside, which let them receive supplies and deliver bags full of sediments to other team members for analysis. The sediment layers formed between 86,000 and 106,000 years ago.

One day in 2012, Dr. Zilhão made an unusual find.

“I was going through the sediment with my trowel and all of a sudden I spotted something and went ‘Wow! Looks like a fish vertebra,’” Dr. Zilhão said. He kept it, shimmied through the passageway and returned to the team so he could show the coin-size object to Sónia Gabriel, a zooarchaeologist at the Portuguese Ministry of Culture.

“When he came out he was like ‘Oh look at this vertebra. Is this a mammal vertebra?’” she said. “And I was like, ‘No, no that’s a fish vertebra — It’s a shark!’”

They later found shark teeth belonging to a different species, which suggested the Neanderthals feasted on a buffet of aquatic animals. The sediment contained bones belonging to eels, morays, conger, mullet and sea bream. They also found burned and cracked claws belonging to brown crabs and spider crabs, and even sea birds. They said this marine life could have made up about half of these Neanderthals’ diet, although they don’t know what was caught directly from the sea or scavenged from creatures that washed ashore or got trapped in tide pools.

In addition to the “surf,” they found plenty of “turf,” such as remains from horses, deer, ibex, aurochs, porcupine and tortoise. Plants were also part of the Neanderthal’s diet as evidenced by pine nuts.

The find from the Portuguese cave taps into ongoing scientific debates about the cognitive sophistication of Neanderthals, and how different the extinct species really was from our earliest modern human ancestors.

Dr. Zilhão said he hoped his finding would help reshape the popular image of Neanderthals as cold-adapted, mammoth hunting brutes.

“The real Neanderthals are like what we’ve been able to show at Figueira,” he said. “They are no different from people living in the same setting and the same environment 100,000 years ago in South Africa or 7,000 years ago across the river in Portugal.”