Dinosaur/Bird Links

I was under the impression that birds have a less-efficient breathing apparatus than mammals (because there are fewer bronchial branches leading to alveoli), but this article maintains the opposite:

A huge carnivorous dinosaur that lived about 85 million years ago had a breathing system much like that of today's birds, a new analysis of fossils reveals, reinforcing the evolutionary link between dinos and modern birds.

The finding sheds light on the transition between theropods (a group of two-legged carnivorous dinosaurs) and the emergence of birds. Scientists think birds evolved from a group of theropods called maniraptors, some 150 million years ago during the Jurassic period, which lasted from about 206 million to 144 million years ago.

...The scans showed small openings in the vertebrae, clavicles (chest bone that forms the wishbone) and hip bones that led into large, hollow spaces. When the dinosaur lived, the hollow spaces would have been lined with soft tissue and filled with air. These chambers resembled such features found in the same bones of modern birds.

...Modern birds have rigid lungs that don't expand and contract like ours. Instead, a system of air sacs pumps air through the lungs. This novel feature is the reason birds can fly higher and faster than bats, which, like all mammals, expand their lungs in a less efficient breathing process.

Other avian air sacs line the spinal column and are thought to lighten birds' skeletal bones, also making flight easier.

"We're beginning to learn more about how the specialized respiratory system of the birds evolved by tracing some of the steps in their ancient relatives," Wilson told LiveScience. "And the cool thing is these animals look nothing like birds."