SCIENCE

Notebook

Mammals Linked to Earlier Flight

Mammals may have taken to the skies much earlier than previously believed, according to research published last week in Nature.

Paleontologists have recovered a fossil of a previously unknown bat- or squirrel-size creature that lived in Mongolia about 125 million years ago. It bears evidence that a skin membrane stretched between the animal's front and rear limbs, providing enough lift for it to glide through the air. The creature, which weighed less than a pound, also apparently had a long, stiff tail that could be used like a rudder in flight, researchers found.

The animal, which is not a direct ancestor of flying squirrels, bats or any other living mammals, lived tens of millions of years before the earliest confirmed record of bats taking wing about 51 million years ago. Before now, the earliest known gliding mammal, a rodent, lived 30 million years ago.

The research, led by Jin Meng, associate curator at the American Museum of Natural History's division of paleontology, shows that there was greater diversity among early mammals than scientists had thought. Indeed, the fossil's discovery points to the existence of an entirely new group of mammals, researchers said.

"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," Meng said.

-- Christopher Lee

Comets Formed at the Solar Core

Astronomers have long believed that comets are composed of interstellar dust and ice. But samples from the comet Wild 2 brought back to Earth by NASA's Stardust space probe found instead a mix of primordial material -- some from the hot inner reaches of the solar system and some from outer regions of the Kuiper Belt, where the comet originated.

In the journal Science last week, researchers detailed their surprising findings that comets may have been spewed from the heart of the solar system during its chaotic birth. The conclusion was based, in part, on the discovery of many high-temperature minerals that could only be formed at the solar core, and at least one grain of a rare mineral -- seen in some meteorites -- formed before the sun's birth.

"Many people imagined that comets formed in total isolation from the rest of the solar system. We have shown that's not true," said Donald Brownlee, the University of Washington astronomer and Stardust's lead scientist.

Astronomers had long believed that comets were made up mostly of ice and tiny dust particles from ancient stars that died and exploded. Instead, they found a mix of ancient materials -- mostly silicates -- that appear to be once-hot particles from the inner solar system that migrated out beyond the cold reaches of Pluto and coalesced to form a comet.