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Galloping sea lions could inspire land-sea robots

Some robots swim and dive through the water; others scurry across the land. Now, researchers want to build a machine that can do both. Their inspiration? The California sea lion.

Though they have a reputation for being lazy, sea lions are fast and graceful underwater. They can also hoof it on land, galloping up to 6.7 meters per second across beaches and even clambering up and own rocks. (Humans are about one-third that fast.)

To help the engineers design a potential land-sea robot, a graduate student recorded three trained California sea lions (Zalophus californianus) as they galloped down a short runway outside (see video above), then analyzed their gaits. She compared that gait with that of elephant seals—which are more than twice as big as sea lions, but also spend time on land. The data showed the sea lion’s ability to pull its hind flippers under its body so that it “walks” like a land animal provides a key advantage both for speed and agility.

True seal hind flippers are off to the side of the body. Consequently, elephant seals can only scooch like an inchworm, lifting their bodies high in the air, dragging in their hind flippers under that mass, and, finally, pulling themselves forward with their front limbs. Sea lions don’t have to lift up their bodies so high, the graduate student reported this week at the virtual annual meeting of the Society for Integrative and Comparative Biology. They can also synchronize pushing with their hind flippers.

The researcher calculated the power output of the sea lion and found that it was more efficient than even harbor and gray seals, making them significantly faster and a better choice for inspiring a robotic marine mammal. So much for being lazy.