University of Michigan paleontologist Jeffrey Wilson, a member of the team that discovered the remains during a 1996 expedition, said the preserved bones of the dinosaur, named Aerosteon riocoloradensis, revealed evidence of air sacs.

The researchers said birds have a breathing system that is unique among land animals. Instead of lungs that expand, birds have a system of bellows, or air sacs, which help pump air through their lungs. That is the reason birds can fly higher and faster than bats, which, like all mammals, expand their lungs in a less efficient breathing process.

Requiring years of cleaning and examination, scientists determined the dinosaur's vertebrae, clavicles and hip bones bear small openings that lead into large, hollow spaces that would have been lined with a thin layer of soft tissue and filled with air in life.

The discovery and subsequent findings are reported in the online journal PLoS One.