The tools and trash that ancient humans left behind provide a window to the past, revealing how they lived thousands of years ago.

Now, scientists want to do the same to study another species — the sea otters. The marine mammals, known for their ability to use tools to open food they cannot crack with their little paws, are the subject of a new study.

Sea Otters' Stone Tools And Trash

An international team of researchers observed and analyzed how sea otters at the Bennett Slough Culvert site in California use shoreline stones to crack open mollusks, particularly mussels. The study, published in the journal Scientific Reports, was conducted over 10 years from 2007 to 2017.

They found that mussels were the primary prey of sea otters in the area. They also found that the mussels were the only prey that the marine mammals crack open using shoreline stones. The researchers estimate that sea otters use shoreline stones in about 20 percent of the mussels they consume.

Through careful observation and analysis, the researchers also noticed that the sea otters tend to pound in the points and ridges of the shoreline rock facing the water, leaving them smoother and lighter in color.

In addition, the team collected the shards of shells left behind by the sea otters and found a consistent damage pattern. The right shell is always cracked, but the left never is.

Combined with videos of sea otters cracking mussel shells with shoreline stones, the study suggested that, like humans, the marine mammals also exhibit "handedness." While they use both paws to hold the shells, they always strike it on the stone with the right paw slightly on top.

Animal Archaeology

The researchers believe that their findings could aid archaeologists who study coastal populations. Their research found patterns that can determine whether humans or sea otters used the stone tool and left behind the shards of mussel shells.

Additionally, the team hopes that their research would lead to more studies that would investigate if the same behavior is exhibited by sea otters in other parts of the world and when they started doing it.

"More broadly, the recovery of past animal behavioral traces helps us to understand the evolution of behaviors like stone anvil use, which is rare in the animal kingdom and is extremely rare in marine animals," stated Jessica Fujii of the Monterey Bay Aquarium. "We hope that this study establishes a new path for the growing field of animal archaeology."

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