Fossil finds have added branches to the sparse early family tree of birds. Most early avian evolution remains unknown because the small, fragile bones of birds rarely survive. But the recent discovery of fossils in Utah and Mongolia could help scientists to map the evolution of flight in birds.
The bones from Utah show that a chicken-sized animal called Avisaurus, thought to be a bird-like dinosaur, was in fact a flying bird, says Howard Hutchison of the Museum of Paleontology at the University of California, Berkeley.
(...) The two creatures lived at roughly the same time, 70 to 80 million years ago in the late Cretaceous period. They came some 70 million years after Archaeopteryx, the first bird.
Avisaurus belongs to an order of primitive birds first discovered in South America in the 1980s. It was initially classed as a two-legged theropod dinosaur because the first bones found came from its dinosaur-like foot. Hutchison found much more complete remains in Utah, including parts of the front limbs; they showed no feather imprints, but the bones had bumps where feathers had been attached.
The skeleton also included some distinctly avian features; shrinkage of the long tail to a small bone called the pygostyle, a wishbone, and a keeled breastbone or sternum to anchor flight muscles. The skull is missing, so it is unclear if Avisaurus had teeth, which many birds retained until the end of the Cretaceous 65 million years ago.
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