'Squirrel' was first mammal to fly 125 million years ago

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A squirrel-like mammal that lived 125 million years ago appears to have discovered flight at about the same time, or even earlier, than the first birds, scientists have found.

The mammal went extinct without leaving any living descendants, but its preserved fossil clearly shows that it was able to glide from tree to tree much like modern-day squirrels and lemurs.

Palaeontologists discovered the mammal's fossil at a site in inner Mongolia where the rock is about 70 million years older that the rock containing the earliest previously known fossils of gliding mammals. The fossil bears the clear impression of a large, fur-covered patch of skin that stretched between the animal's forelimbs and hindlimbs, which was used as an aerofoil in gliding flight.

Scientists working at the American Museum of Natural History in New York and the Chinese Academy of Sciences in Beijing yesterday published the first detailed description of the ancient mammal, which they have called Volaticotherium antiquus, in the journal Nature.

The mammal is so unusual and highly specialised that it has no known contemporary relatives. It also possessed a long, stiff tail that was probably used as a rudder to control its direction of movement through the air. Gliding flight has evolved independently many times in vertebrates, but birds and bats are the only members of the group today that are able to fly using flapping wings controlled by powerful muscles.

Volaticotherium antiquus, which means "ancient gliding beast" in Latin, lived at a time when the dinosaurs were the dominant land animals. It was not until after the dinosaurs died out about 65 million years ago that mammals became the largest land animals.

The animal weighed about one pound and lived on a diet of small insects which it probably caught while clambering through the tree tops. Its agility in the air was probably not good enough to catch its prey in flight, and it almost certainly glided from tree to tree either to extend its territory or to escape from predators, according to the scientists.

"This discovery extends the earliest records of gliding flight for mammals to at least 79 million years earlier in geological history," they say in Nature. "They had experimented with an aerial habit at about the same time as, if not earlier than, when birds endeavoured to exploit the sky," they say.

Jin Meng, associate curator of the American Museum of Natural History, said that the mammal had elongated limbs to help it to maintain aerodynamic lift, and its finger and toe bones were adapted to tree climbing.

"This new evidence of gliding flight in early mammals is giving us a dramatically new picture of many of the animals that lived in the age of the dinosaurs," Dr Meng said.

The scientists believe that this discovery marks one of the most important finds in the study of ancient mammals for more than a century.

"Establishing a new order [a group of mammals] probably only happens once, if that, in the lifetime of a lucky paleaomammalogist," Dr Meng said. Before the latest discovery, the earliest known gliding mammal was a rodent known from a 30 million-year-old fossil, which also had a preserved gliding membrane. The earliest fossil of bats is dated to around 51 million years ago whereas the earliest fossils of ancient birds with feathers date back to more than 125 million years ago.