Walking on two legs, along with opposable thumbs and braininess, is supposed to be what makes humans human. But a couple of bipedal beasts are challenging that concept.
Duopus: In 2000 in Indonesia, biologist Christine Huffard of the University of California at Berkeley noticed an Octopus marginatus strolling slowly along a sandy bottom on two arms, gathering the remaining six around its body as a disguise. This marks the first known instance of bipedal locomotion in an animal without a rigid skeleton. This might have been an anomaly, but a similar sight greeted her three years later in Australia, where the smaller Octopus aculeatus tiptoed along in the shape of an algae cluster, raising the possibility that the behavior is normal for the invertebrates. How could two arms be better than eight? “Most octopuses have to give up camouflage to move quickly, making it risky for one to escape from a nearby predator that might not have seen it yet,” Huffard says. “Walking behavior may allow them to lessen risk and escape under the predator’s radar.”
Bat bipeds: Several species of bat are known to use their strong forelimbs and weak hind legs to crawl along the ground, but no one suspected they might be able to run. At least not until Cornell University biologist Daniel Riskin dropped a common vampire bat onto a treadmill, only to be stunned as it broke into a bounding run. Running, Riskin hypothesizes, evolved independently when the bats relied on small, ground-dwelling prey. “Cows are the main food source for common vampire bats, but there were no cows in Central and South America when vampire bats evolved,” says Riskin. Vampire bats are nothing if not sneaky, and at close quarters, lying low is probably more unobtrusive than a nosedive.