A sparrow-size creature of 135 million years ago appears to be the oldest known bird that lived in trees and flew with agility, a researcher says.

The creature's feet showed that it lived in trees, while its wing bones, breastbone and short clump of tail bones suggest an ability for long-range flight, said Paul Sereno, who analyzed a fossil of the bird.The bird, not yet officially named, followed a primitive bird called Archaeopteryx by about 10 million years.

Archaeopteryx, which retained many dinosaur characteristics, was basically a ground-dwelling bird that probably could climb trees, jump and flap its wings to propel itself, Sereno said. But its flight may have been rather short-range, he said.

The findings challenge assertions by some scientists that birds essentially lived on the ground for 50 million to 100 million years after Archaeopteryx, he said.