Sea otter archaeology could tell us about their 2-million-year history

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    Sea otter archaeology could tell us about their 2-million-year history
    Sea otter (Enhydra lutris) breaking open a clam with a rock.

    A sea otter breaks open a clam with a rock

    Thomas & Pat Leeson/SPL

    By Michael Le Page

    Archaeology is defined as the study of human history and prehistory by the analysis of physical remains. But the dictionaries may need rewriting – archaeology is now being used to study the cultural histories of tool-using animals, from sea otters and monkeys to birds and even fish.

    Natalie Uomini at the Max Planck Institute for the Science of Human History in Germany and her colleagues have analysed a site at Bennett Slough Culverts in California where sea otters use rocks as tools for cracking open mussels. At this site, the otters don’t just place smallish stones on their chest and then crack the shellfish on them.

    Unusually, they also bash mussels against large rocks on the seashore, creating huge piles of broken shells. Uomini’s team has shown that this leaves distinctive wear patterns on the large rocks used as anvils and also breaks the shells in a characteristic way, meaning the shell middens left by sea otters can be distinguished from those left by, say, people.

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    This means it should be possible to identify ancient sites where sea otters used large stones in this way, which could reveal whether sea otters have been using stone tools ever since they first evolved about 2 million years ago. This would involve the same techniques used for the study of ancient human sites.

    However, finding ancient sea otter sites won’t be easy, not least because many surviving sites may be underwater due to sea level rise. “It’s really hard,” says Uomini.

    She is also studying New Caledonian crows, which are famed for their tool use. Although most of their tools are twigs and other items that rapidly break down, some do use stone anvils.

    Many other birds drop hard food items on stones to get into them, and there are even fish that break open shells on rocks. “We’d like to expand the concept of archaeology to non-humans,” says Uomini.

    “Archaeology can be applied to any species that produces a durable material signature,” says Tomos Proffitt at University College London, who has studied the sites left by capuchin monkeys that use stones to crack nuts.

    He doesn’t think his fellow archaeologists will object to the idea of expanding the discipline. “I think the vast majority of archaeologists probably wouldn’t care,” says Proffitt. “The material culture of animals is not massively on the radar of most archaeologists.”

    Journal reference: Scientific Reports, DOI: 10.1038/s41598-019-39902-y

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