Gliding dinosaurs are birds' missing link
Posted: Thursday, January 23, 2003
by Mark Henderson
Fossils found in China of a winged and feathered dinosaur indicate that birds evolved from a line of tree-dwelling raptors
A SPECTACULAR set of fossils belonging to a winged and feathered dinosaur has been unearthed in China, providing one of the final missing links in the evolution of birds.
Microraptor gui, a new species that lived about 128 million years ago, used four feathered limbs to glide from tree to tree like a flying squirrel - a "halfway" means of flight by which the first birds probably took to the skies.
The small predator, which grew to about two and half feet long, will settle a long-running debate about how the cousins of Tyrannosaurus rex and Velociraptor evolved into modern birds.
It is the first truly intermediate fossil that is part-dinosaur and part-bird. Its unique physical traits indicate that birds emerged from a line of small, tree-dwelling dinosaurs, which first learnt to glide as they hunted, or were being hunted, and progressed to flight.
This would rule out the theory that flight originated among ground-based feathered dinosaurs. Only last week, a study of modern partridges suggested a way in which such creatures might have learnt to take off, by flapping their forelimbs for thrust and traction.
Microraptor gui belongs to a group of theropod or predatory dinosaurs known as the basal dromaeosaurids, which most experts accept as the ancestors of birds. It had feathers arranged aerodynamically on its fore and hind limbs, and its long, streamlined tail.
This combination of wings and a tail would have been ideal for gliding, instead of running on the ground, where the leg feathers would have got in the way.
Xing Xu, of the Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing, who led the research team, said that the forelimb and leg feathers would have made a perfect aerofoil, similar to a batís stretched web of skin.
"These features together suggest that basal dromaeosaurids probably could glide, representing an intermediate stage between the flightless non-avian theropods and the volant (flying) avians."
The research suggested that the new species first learnt to glide, "by taking advantage of gravity, before flapping flight was acquired".
Six specimens of the creature, which is named after the distinguished Chinese palaeontologist Gu Zhiwei, have been discovered in Liaoning Province in northeastern China, and details are published today in the journal Nature.
Over the past five years, dozens of feathered dinosaur remains have been found in Liaoning, suggesting that theropod dinosaurs were the ancestors of birds - as was first suggested by Thomas Henry Huxley as early as 1868. Previous finds, however, have belonged to feathered but flightless creatures such as "fuzzy raptor", one of the centrepieces of the "Dino-Birds" exhibition on display at the Natural History Museum in London.
Microraptor gui appears to confirm the work of the naturalist William Beebe, who in 1915 proposed that the first flying birds were gliders, equipped with wing feathers on both arms and legs.
Richard Prum, an evolutionary biologist at the University of Kansas, said that the new fossil "looks as if it could have glided straight out of Beebeís notebooks. The discovery provides striking support for the arboreal-gliding hypothesis of the origin of bird flight."
Microraptor gui and the other dinobirds of Liaoning lived between 128 million and 122 million years ago, making them much younger than Archaeopteryx, which at 147 million years is the most ancient bird known to science.
The discoveries carry huge evolutionary significance because Archaeopteryx is a close relation, and, though older, is likely to have developed from a feathered dromaeosaur similar to Microraptor.
"It looks confusing that this is later in time than Archaeopteryx, but that does not make this discovery any less stunning," said Angela Milner, associate keeper of palaeontology at the Natural History Museum.
"It is just an accident of preservation." The evidence now points overwhelmingly to a treetop origin for modern birds, Dr Milner said. "We are looking at small, agile dinosaurs with very curved claws, adapted for climbing trees," she said. "It looks as if feathers evolved first for insulation."
The evolutionary trail
Microraptor gui: 128-124 million years ago; c 2 ft long. Newly-discovered "missing link" between dinosaurs and birds that used four feathered limbs to glide from tree to tree.
Archaeopteryx: 147 million years ago. First known bird - toothed beak, feathered wings capable of powered flight. Probably evolved from creature similar to Microraptor gui.
Dromaeosaurs: Feathered dinosaurs living 130-120 million years ago. Mostly flightless predators; used feathers for insulation. Include Microraptor gui and "fuzzy raptor" fossil on display at Natural History Museum.
Sinornithosaurus millenii: 124 million years ago. Dromaeosaur covered in downy feathers. First complete skeleton of a feathered dinosaur discovered.
Protarchaeopteryx and Caudipteryx: 130-120 million years ago. Feathered, flightless dino-birds discovered in Liaoning province in 1997. Had fans of tail-feathers.
Archaeoraptor liaoningensis: Elaborate fake, announced in 1999 as the "missing link" between dinosaurs and birds. Turned out to be two fossils stuck together - the bottom half of a dromaeosaur, and the top half of a primitive bird, Yanornis martini.
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