The oldest fossilised bats ever discovered have given palaeontologists an unprecedented insight into the flying mammals' evolution. The find puts to rest a long-standing argument over which came first, flight or echolocation - the bats' exotic navigation system. The new species of bat could fly, but didn't use echolocation.
"When we first saw it, we knew it was special," said Dr Nancy Simmons at the American Museum of Natural History in New York, who was part of the team. "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."
Scientists have wrestled with three alternative theories for the evolution of bats: flight evolved before echolocation; echolocation came before flight; or both happened in parallel. The new pair of fossils - which date from around 52.5m years ago - resolve the issue.
"There has been much debate about how bats evolved, because there were no specimens to address this issue," said Dr Kevin Seymour at the Royal Ontario Museum in Toronto. "Now the combination of features seen in this species finally gives us an answer: that flying evolved first and echolocation must have evolved later."
Fluttering and gliding
The wing bones clearly show that the animal was capable of a combination of fluttering and gliding flight. But its ear bones are not enlarged like those of modern bats, which use them as part of their echolocation system.
The first fossil was discovered in August 2003 in a quarry in Lincoln County, Wyoming, but the full scientific description appears for the first time in tomorrow's issue of Nature. The species (dubbed Onychonycteris finneryi) is so odd that it has been placed in a new taxonomic family. Its name means "clawed bat" with a nod to the fossil's discoverer Bonnie Finney.
O. finneryi - which is around 12 centimetres from nose to tail - has claws on all five of its fingers. Modern bats have claws on only one or two digits of each hand. Its limb proportions are also unusual, with longer hind legs and shorter forearms than other bats. The researchers believe it was well adapted for climbing in the canopy.
One unanswered question is how O. finneryi could have flown without being able to echolocate. Also writing in Nature, physiologist Prof John Speakman of the University of Aberdeen speculates that the earliest bats were day-fliers who used their eyes to navigate.
"[They] were perhaps forced to become nocturnal by the appearance of avian predators, shortly after the dinosaurs became extinct around 65m years ago. Some then evolved echolocation, whereas others became nocturnal vision specialists."