Wings Aplenty: Dinosaur species had feathered hind limbs

A team of Chinese paleontologists has discovered two nearly complete fossils of a small, feathered dinosaur that they say had four wings. The new species may represent an intermediate on the path to today’s birds.

ANCIENT GLIDER. Artist’s concept of Microraptor gui, a newly discovered feathered dinosaur. P. Sloan

The slim creature, which the paleontologists dubbed Microraptor gui, measured nearly 1 meter from its snout to the tip of its feathered tail and lived about 130 million years ago in what is now northeastern China. Besides having forelimbs that resemble the wings of modern birds, the animal sported long feathers from thigh to foot on each hind limb.

Despite their plumage, these hind limbs probably didn’t flap to provide propulsion. M. gui may have glided from tree to tree like today’s flying squirrels do, speculates a research team led by Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. The front and rear limbs on each side of the animal would make a perfect airfoil if they were held together to form one continuous surface, the researchers note in the Jan. 23 Nature.

Several of the dozen or so large feathers on each of M. gui‘s limbs were asymmetrical: the vane on one side of the feather’s spine was wider than the one on the other. This nuance of design strongly suggests these feathers served an aerodynamic purpose, says Richard O. Prum of the University of Kansas in Lawrence.

The added wing area from M. gui‘s feathered hind limbs would have reduced the angle of its glide and thus increased the distance each glide covered, says Jeremy M.V. Rayner, an evolutionary biologist at the University of Leeds in England.

Not all paleontologists are convinced that the creature used its hind limbs as wings.

For one thing, says Kevin Padian, a paleontologist at the University of California, Berkeley, it’s difficult to imagine how M. gui could extend its hind limbs sideways to form a horizontal flight surface. Unless the creature had a hip joint configuration unlike that of any other bird or theropod dinosaur, splaying its legs for flight “would dislocate the hip joint completely,” Padian notes. Nevertheless, he adds, M. gui clearly has more feathers than any other nonavian theropod yet described.

M. gui‘s sternum didn’t have a keel upon which large flight muscles could be attached. So, Prum notes, “it’s pretty clear this animal was a glider.” Detailed analyses of its joints should shed more light on whether the animal could maneuver its legs into a horizontal flight position.

Archaeopteryx, considered by most paleontologists to be the first bird, lived about 150 million years ago and was described by scientists in 1861. “If the evidence is right, [M. gui] would be the most remarkable find in bird evolution since Archaeopteryx,” Rayner says.

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