A well-preserved fossil of a previously unknown species of bat has resolved an evolutionary conundrum - could bats fly before they could echo-locate their insect prey?

The new species, named Onychonycteris finneyi, was unearthed in 2003 in the Green River formation in southwestern Wyoming. This area is rich in fossils, and it was here that the earliest known bat fossil, Icaronycteris index was found in the 1960s.

Icaronycteris index had cranial features suggesting that it could locate its insect prey by echolocation, sparking a debate about bat evolution.

Did they need to be able to echolocate before they could fly?

Onychonycteris finneyi dates from the Early Eocene, preceding Icaronycteris, and is a possible intermediate form between bats and their non-flying, non-echolocating mammalian ancestors.

While its limbs indicate it may have been an agile climber, it has fully developed wings and was capable of powered flight.

However, the morphology of the ear region suggests Onychonycteris finneyi could not echolocate.

52 Million-Year-Old Fossil Bat

The discovery, by Nancy Simmons of American Museum of Natural History (AMNH) in New York, and her colleagues resolves an ongoing debate about the evolution of bats, showing that they could fly before they acquired their famous ability to use echolocation to hunt and navigate.

The fossil is described in the February 14 issue of the journal Nature, and a cast of the fossil is on permanent display in the University of Michigan Exhibit Museum of Natural History's Hall of Evolution.

Bats represent one of the largest and most diverse orders of mammals, the Chiropterae, about one-fifth of all living mammal species.

The well-preserved fossil Onychonycteris allowed scientists to take an unprecedented look at the most primitive known member of the order Chiroptera.

"When we first saw it, we knew it was special," said lead author Nancy Simmons of AMNH.

"It's clearly a bat, but unlike any previously known. In many respects it is a missing link between bats and their non-flying ancestors."

Dating the rock formation in which the fossil was found put its age at 52 million years.

Echolocation Debate Resolved

“There has been a longstanding debate about how bats evolved, centering around the development of flight and the development of the sonar system they use to navigate and hunt for prey," said paleontologist Gregg Gunnell, an associate research scientist at the U-M Museum of Paleontology and joint author of the Nature paper.

"The three main theories have been that they developed the two abilities together, that flight came first, or that sonar came first.

“Based on the specimen described in this paper, we were able to determine that this particular animal was not capable of echolocating, which then suggests that bats flew before they developed their echolocation ability."

The fossil revealed several surprising physical features. Onychonycteris had claws on all five of its fingers, where modern bats have, at most, claws on only two digits of each hand.

Its limb proportions were also different from all other bats. The hind legs were longer and the forearm shorter, similar to those of climbing mammals that hang under branches, such as sloths and gibbons.

Gunnell said the fossil's limb form and the appearance of claws on all the fingers suggest that it may have been a skilled climber.

However, long fingers, a keeled breastbone and other features indicate that Onychonycteris could also fly.

It had short, broad wings, so it probably could not fly as far or as fast as most bats that came after it.

Instead of flapping its wings continuously it may have alternated flapping and gliding.

"We don't know what the initial incentive was to take to the air," Gunnell said.

"These bats probably were commuters at first--- the ability to fly allowed them to travel to a particular place to feed, then fly back to their nesting area."