Primitive Bats Took to the Wing, but They Didn't Have That Ping

February 13th, 2008With more than 1,100 species living across the world, bats are the second most numerous type of mammal, after rodents.

Their success comes in large part from two evolutionary jumps more than 50 million years ago. They can fly " the only mammals that can " and most also possess the sonarlike ability to locate objects, like the insects they want to eat, by emitting high-pitched sonic pulses and then triangulating the echoes bouncing back to their oversize ears.

The lack of fossils of the earliest bats have left scientists pondering the question of which evolved first: flight or sonar?

Or might the two abilities have evolved in tandem?

Writing in Thursday's issue of the journal Nature, scientists led by Nancy B. Simmons of the American Museum of Natural History in New York City describe a bat that lived 52.5 million years ago that strongly suggests flight came first.

Two fossils of the species, named Onychonycteridae finneyi, have been found in the rocks of Wyoming. The fossils date from the same time as the previously oldest-known species, which was discovered in the same area four decades ago.

But the new species clearly is more primitive, the researchers said.

For one, it has claws at the end of every finger. All bats, present and extinct, have a claw at their first finger, the thumb. Some also have a claw on the index finger.

But until now, scientists had not seen claws on the other three fingers of any bat. (The name Onychonycteridae means "clawed bat"; finneyi is a tribute to a fossil collector, Bonnie Finney, who found it in 2003.)

This bat also appears to lack the adaptions that are believed necessary for the sonar ability, also known as echolocation, like an enlarged cochlea, the part of the inner ear that converts sound vibrations into nerve signals.

Instead, its skeleton more closely resembles those of a still-living lineage known as old world fruit bats, which do not echolocate. (Those bats eat fruit or flower nectar, not insects, and thus perhaps have less need for tracking fast-moving objects.)

The primitive features of Onychonycteridae place it close to the base of the bat family tree.

�This discovery basically supports the flight-first hypothesis,� Dr. Simmons said.

The eye sockets of both fossils were crushed, so the scientists could not tell whether the bat had the large eyes of many nocturnal animals. (It very likely was not blind as a bat, however. That idiom is not true; most bats can see quite well.)

Source: NYT