View Full Version : Bats Flew First, Developed Echolocation Later, Fossilized Missing Link Shows


Knight-Dragon
Feb 13, 2008, 08:07 PM
http://www.sciencedaily.com/releases/2008/02/080213121444.htm

ScienceDaily (Feb. 13, 2008) — The discovery of a remarkably well-preserved fossil representing the most primitive bat species known to date demonstrates that the animals evolved the ability to fly before they could echolocate. The new species, named Onychonycteris finneyi, was unearthed in 2003 in southwestern Wyoming. Bats represent one of the largest and most diverse orders of mammals, accounting for one-fifth of all living mammal species. The well-preserved condition of the new fossil permitted the scientists to take an unprecedented look at the most primitive known member of the order Chiroptera.

"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 Gregg Gunnell, an associate research scientist at the University of Michigan Museum of Paleontology. "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 research is described in the Feb. 14 issue of the journal Nature, on which U-M paleontologist Gregg Gunnell is a coauthor along with researchers from the American Museum of Natural History (AMNH) in New York, the Royal Ontario Museum in Canada and the Senckenberg Research Institute in Germany. A cast of one of the two known specimens is on permanent display in the U-M Exhibit Museum of Natural History's Hall of Evolution.

"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. Onychonycteris was not the only bat alive at the time---fossils of Icaronycteris, a more modern bat that could echolocate, are found in the same formations.

A careful examination of Onychonycteris's physical characteristics revealed several surprising features. For example, it had claws on all five of its fingers, whereas modern bats have, at most, claws on only two digits of each hand. The limb proportions of Onychonycteris are also different from all other bats---the hind legs are longer and the forearm shorter---and more similar to those of climbing mammals that hang under branches, such as sloths and gibbons.

The fossil's limb form and the appearance of claws on all the fingers suggest that Onychonycteris may have been a skilled climber. However, long fingers, a keeled breastbone and other features indicate that Onychonycteris could fly under its own power like modern bats. It had short, broad wings, which suggest that it probably could not fly as far or as fast as most bats that came after it. Instead of flapping its wings continuously while flying it may have alternated flapping and gliding while in the air. Onychonycteris's teeth indicate that its diet consisted primarily of insects, just like that of most living bats.

"We don't know what the initial incentive was to take to the air," Gunnell said. "My thought is that these bats probably were commuters at first---developing the ability to fly allowed them to travel to a particular place to feed, then fly back to their nesting area." Eventually, selective pressures likely favored the development of more sustained and agile flight, allowing bats to hunt on the wing.

Despite Onychonycteris's resemblance to animals that came after it, its skull lacks features in and around the ear seen in bats that use echolocation to navigate and hunt. The structure of its feet and ankles, which include a special, spur-like bone that likely supported a tail membrane, led the researchers to conclude that Onychonycteris had the broad tail that modern bats use to capture prey in flight, but that the structure probably was used as an airfoil to aid maneuvering. Without echolocation, Onychonycteris likely had to make do with visual, olfactory, or passive audio cues to hunt.

"It finally gives us an answer," Simmons said. "Flying evolved first, echolocation second."

In addition to Simmons and Gunnell, the paper's authors include Kevin L. Seymour of the Royal Ontario Museum and Jörg Habersetzer of the Senckenberg Research Institute in Germany.

Funding for the work was provided by the U.S. National Science Foundation (NSF) and Deutsche Forschungsgemeinschaft (DFG).

Adapted from materials provided by University of Michigan.
http://www.sciencedaily.com/images/2008/02/080213121444.jpg
Fossil Bat. (Credit: Photo credit and copyright: American Museum of Natural History)

Leifmk
Feb 14, 2008, 02:26 AM
Well, even today there are diurnal bats who do not use echolocation.

Eran of Arcadia
Feb 14, 2008, 08:11 AM
This implies (at least to me) that little is known about how/when bats developed flight - a shame, because it is one of only (I think) 4 times in the history of the earth that it happened.

warpus
Feb 14, 2008, 09:59 AM
This implies (at least to me) that little is known about how/when bats developed flight - a shame, because it is one of only (I think) 4 times in the history of the earth that it happened.

Don't we know how that happened?

Aren't there squirrels that glide? Wouldn't it have happened the same way?

Eran of Arcadia
Feb 14, 2008, 10:00 AM
Okay, maybe little was known to me. But it seemed like they didn't actually know when, if they weren't sure when it was in relation to echolocation.

warpus
Feb 14, 2008, 10:03 AM
Ahh.. Well, I'm not sure either, but it seems to make sense to me. Bats are mammals, just like squirrels.. and those gliding squirrels look a bit like bats, at least to me.

Masquerouge
Feb 14, 2008, 12:53 PM
This implies (at least to me) that little is known about how/when bats developed flight - a shame, because it is one of only (I think) 4 times in the history of the earth that it happened.

It is? What are the four?
If I think about it I have:
- mammals (bats)
- dinosaurs (birds)
- whatever order the flying reptiles such as pteranodon belonged to (pterodactyles?)
- insects. are all flying insects descending from one single common ancestor? Some have two wings and other 4, doesn't that mean we have at least two different ways that flying evolved in insects?

Eran of Arcadia
Feb 14, 2008, 12:57 PM
Alright, now that you mention it I am not sure about insects, it would make sense to me that all flying insects have a common flying ancestor, but I don't know. I think I read that they did. And yes for the others (pterosaurs being the name of flying non-avian reptiles in general).

Masquerouge
Feb 14, 2008, 12:58 PM
Alright, now that you mention it I am not sure about insects, it would make sense to me that all flying insects have a common flying ancestor, but I don't know. I think I read that they did. And yes for the others (pterosaurs being the name of flying non-avian reptiles in general).

Come to think of it, that would make a great quizz question :)

And maybe, given enough time, we will have truly flying fishes.

lordqarlyn
Feb 14, 2008, 05:11 PM
Ahh.. Well, I'm not sure either, but it seems to make sense to me. Bats are mammals, just like squirrels.. and those gliding squirrels look a bit like bats, at least to me.

Are bats from the same line as rodents? I always thought they came from a different line.

warpus
Feb 14, 2008, 06:15 PM
I have no idea.. This is a gliding squirrel though:

http://upload.wikimedia.org/wikipedia/commons/8/8f/Jill_Flying_1.jpg

Would make sense that this is how bats evolved the ability to fly, no? They used to live on trees, evolved the ability to glide, and it eventually turned into flight.

At least that's my guess :)