Thursday, February 14, 2008
Scientists unearth most primitive bat ever found
Bats flew before they had 'radar,' fossil shows
A fossil found in Wyoming has apparently resolved a long-standing question about when bats gained their radarlike ability to navigate and locate airborne insects at night.
The answer: after they started flying.
The discovery revealed the most primitive bat known, from a previously unrecognized species that lived about 52 million years ago.
Its skeleton shows that it could fly but lacked a series of bony features associated with echolocation, the use of high-pitched sounds to locate objects and prey in the surrounding environment, researchers said.
Until now, all the early known fossil bats showed evidence of both flying and echolocating, so it couldn't be determined which ability came first, said researcher Nancy Simmons.
Her team's research appears in today's issue of the journal Nature. Simmons chairs the vertebrate zoology division at the American Museum of Natural History in New York.
The early bat's wingspan was nearly a foot, just a bit less than that of today's big brown bat, she said.
Its teeth show that it ate insects, which it evidently plucked off surfaces after seeing, smelling or hearing them, she said.
Simmons said she suspects that the bat was active at night but that there's no evidence of that.
The creature was unusual in having a claw on all five fingers rather than just one or two.
The most primitive bat ever found fluttered around about 52 million years ago, but lacked a key feature seen in most bats -- the ability to echolocate, hunting and navigating using a kind of sonar.
A team of scientists announced the discovery on Wednesday of a medium-sized ancient bat called Onychonycteris finneyi that possessed fully developed wings and was completely capable of flying. But they said that based on the evidence from its skeleton it lacked the ability to echolocate.
Kevin Seymour of the Royal Ontario Museum in Canada, one of the scientists who describe it in the journal Nature, said this bat appears to settle a long-standing debate of which came first in bats -- echolocation or flight. The answer is flight.
"It is like this is sort of half way to being a modern bat. It's the most primitive bat that we know. It could clearly fly. But it could not echolocate. The evidence from the skull and throat region shows us none of the features that echolocating bats have," Seymour said in a telephone interview.
Bats are the second most common type of mammal living today, constituting a fifth of all mammal species. Only rodents, which make up half of mammals, are more plentiful.
Bats also are an ancient form of mammals, and scientists have struggled to understand their early evolutionary history. Onychonycteris, unearthed in 2003 in southwestern Wyoming, appears to be filling in some important gaps.
"It's clearly a bat, but unlike any previously known," Nancy Simmons of the American Museum of Natural History in New York said in a statement. "In many respects it is a missing link between bats and their nonflying ancestors."
Echolocation is a form of sonar used by several mammals to navigate and hunt. They use high-pitched sounds to find the location of objects by the sounds reflected from them. Most bats use it to find flying insects to catch in mid-air. Other mammals with this ability include whales, dolphins and shrews.
The scientists called the fossil of Onychonycteris beautifully preserved, representing a previously unknown bat family. But while they call it the most primitive bat, they said a bat with more modern features, Icaronycteris, lived at the same time. Icaronycteris used echolocation, they said.
Seymour said there is nothing unusual about more primitive forms living alongside more advanced ones. "That's completely normal. Think today of the monotremes living in Australia, the egg-laying mammals," Seymour said. These include the platypus.
The wingspan of Onychonycteris was about 12 inches. It had short, broad wings, suggesting it probably could not fly as quickly as most bats that appeared later. Rather than flapping its wings continuously while flying, it may have alternated flapping and gliding while in the air.
Its teeth suggest its diet consisted mostly of insects, like most bats today. It had claws on all five of its fingers, while modern bats have them on only one or two digits of each hand. Its limb proportions are different from all other bats.
Seymour said scientists are not certain from what type of mammal bats evolved, but it could have been a tree-dwelling insectivore like a shrew.
Bats are one of only three types of vertebrates in the history of Earth to develop the ability to fly, joining the flying reptiles called pterosaurs, which went extinct 65 million years ago, and birds.