Bobbing off the coast of western America, sea otters may have been using stone tools before we, as a species, even existed. It turns out that the marine mammals have been smashing shells on an anvil made of rock for thousands – and perhaps even millions – of years.
Sea otters are known to be prolific tool users. The marine mammals collect rocks from the ocean floor, which they then balance on their bellies and use as anvils on which to smash shellfish to get at the tasty meat within. The otters are even known to have favorite rocks, which they then store in moist pockets of skin for use at a later date. But not all individuals within a population will use tools, raising the question of whether or not the skill is learned.
This has an interesting parallel with another tool-wielding marine mammal – the Indo-Pacific bottle-nosed dolphin. These cetaceans use cone-shaped sponges to protect the ends of their beaks from damage as they sweep the seafloor in search of fish hiding in the sand. Again, not all dolphins are known to do this and those that do are likely closely related, suggesting it is a recent cultural development passed on from mothers to offspring.
The otters often have a "favorite" tool that they store in a pouch. David Litman/Shutterstock
To see if this might be the same for the shell-cracking otters, the team of scientists did genetic tests on those that use tools to see how closely related they are compared with the wider population. To their amazement, they found that the groups were incredibly diverse and no more closely related to each other than they were to the population of otters in general.
“The lack of genetic association with tool-use in sea otters, compared with dolphins, may result from the length of time each species has been using tools,” write the authors in their study published in Biology Letters. “Tool-use in dolphins is thought to be a recent innovation; however, it is likely a much older behaviour in sea otters.”
Munching on a tasty treat. Chase Dekker/Shutterstock
They suggest that wide genetic differences between tool-using otters implies that the behavior probably came into being at least thousands, and possibly even millions, of years ago, massively pre-dating the tool use of Indo-Pacific dolphins, which is only thought to be around 200 years old.
This is supported by the fact that young sea otter pups seem innately predisposed to using tools. They refer to orphaned otter pups raised in captivity that learn how to use the stones even before they are weaned.
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