Sea Otters Leave an Archaeological Record of Their Tool Use

Archaeologists learn about ancient humans by excavating and analyzing historical artifacts. While the use of tools was once thought to be a uniquely human trait, this is far from the case; many terrestrial animals, including chimpanzees, macaque monkeys, and even vultures use stone tools to hunt and gather food. For aquatic animals, however, these behaviors have been difficult to observe in the wild. One exception is sea otters, which use large stone “anvils” found along the seashore as tools to smash open mussels that are too difficult to open with their paws. By combining techniques from zoology and archaeology, “animal archaeologists” are beginning to learn more about the history of sea otter tool use.

In a new study, an international group of biologists and archaeologists tracked the mussel eating behavior of sea otters at California’s Bennett Slough Culverts site over a 10-year period. They found that otters used anvils to open around 20% of the mussels they captured, leaving behind a stereotypical damage pattern on the anvils, distinct from human use or weather erosion. When using anvils, otters preferentially targeted water-facing points and ridges as pounding surfaces, rather than flat or land-facing surfaces. Additionally, the discarded mussel shells found around the anvils had a consistent diagonal fracture on their right side, indicating that sea otters smash open their dinner with a characteristic motion (and that they are predominantly right-handed)!

Once an abundant species in the wild, sea otters have experienced a dramatic fall in numbers due to the fur trade. By uncovering the archaeological signature of stone anvil use, scientists are now poised to better track the migration patterns of this now endangered species, as well as date how far back in time anvil use goes. More broadly, further work in the burgeoning field of animal archaeology may reveal the evolution of additional rare animal behaviors.

Managing Correspondent: Benjamin Andreone

News Article: Archaeological Evidence Shows How Animals Are Mastering The Use Of Stone Tools. Forbes

Original Article: Wild sea otter mussel pounding leaves archaeological traces. Scientific Reports

Image Credit: Jessica Fujii/Monterey Bay Aquarium