Flight without sonar

Bats are famous for their ability to use sound to “see.” The technique, called echolocation, involves making high-pitched sounds that bounce off objects and return to the animal. On the basis of the pattern of sound that comes back, a bat gets a good picture of what’s out there.

More than one-fifth of mammal species alive today are bats. And most bats use echolocation to find prey and avoid bumping into things as they fly. But bats didn’t always have such supersensory skills, say scientists who have found a fossil of one of the world’s most ancient bats.

This ancient bat, called Onychonycteris finneyi, could fly but probably not echolocate.

Royal Ontario Museum

The new find feeds an old debate: Which came first for bats—flying or echolocation?

Scientists from the American Museum of Natural History in New York City found the fossil in western Wyoming. The bones come from a bat called Onychonycteris finneyi, which lived about 52.5 million years ago. The animal’s wingspan measured 30 centimeters (12 inches) wide. It was about the size of a cardinal bird.

The ancient bat looked different from modern bats. For one thing, it had claws on all five digits of its front limbs. Living bats (and previously studied fossil bats), on the other hand, have claws on no more than two digits of each front limb.

O. finneyi‘s wings were shorter and broader than those of other bats. And the part of the wing that stretched between the bat’s fingers was relatively small. Modern species that are built this way have an odd way of flying: They take turns gliding and flapping their wings.

This flying style is clumsy, but it saves energy. And it might represent the evolutionary transition from gliding to true flying. What’s more, some of O. finneyi‘s other features resemble those of animals that live in trees but don’t fly, such as sloths and lemurs. Together, these traits suggest that O. finneyi belonged to one of the most primitive groups of bats.

Previously, scientists had found fossils from six other species of bats that lived between 54 million and 50 million years ago. All six appear to have been able to both fly and echolocate.

O. finneyi, it is now clear, could definitely fly. But the well-preserved fossils reveal the primitive bat’s inner ear was small, which suggests that it could not echolocate. This means, scientists think, that bats developed the ability to fly before they developed the ability to echolocate.

“This is a really big find, a huge piece of the [evolutionary] puzzle,” says Emma C. Teeling, a paleontologist at University College Dublin.

Going Deeper:

Perkins, Sid. 2008. Flying deaf? Earliest bats probably didn’t echolocate. Science News 173(Feb. 16):99. Available at http://www.sciencenews.org/articles/20080216/fob1.asp .

Sohn, Emily. 2008. Hearing whales. Science News for Kids (Feb. 13). Available at http://www.sciencenewsforkids.org/articles/20080213/Note2.asp .

______. 2007. How to fly like a bat. Science News for Kids (May 9). Available at http://www.sciencenewsforkids.org/articles/20070509/Feature1.asp .

Webb, Sarah. 2006. Echoes of hunting. Science News for Kids (April 26). Available at http://www.sciencenewsforkids.org/articles/20060426/Feature1.asp .