A 33-foot long, carnivorous dinosaur that lived 85 million years ago had a breathing system similar to that used by modern birds, and researchers say the finding is further evidence of the evolutionary link between dinosaurs and birds. A fossil found in a riverbank in Argentina shows evidence of efficient air sacs that pumped air into the dinosaur's lungs. Lead researcher Paul Sereno named the new dinosaur Aerosteon riocoloradensis, which means "air bones from the Rio Colorado."
Instead of lungs that expand and contract, Sereno thinks this beast had air sacs that worked like a bellows, blowing air into the beast's stiff lungs, much like modern birds.... Most paleontologists believe birds evolved from small, feathered meat-eating dinosaurs, and the earliest known birds were strikingly similar to these dinosaurs [Reuters].
Verifying that dinosaurs had bird-like breathing systems has been difficult because lungs do not fossilize, according to Sereno. In Argentina, Sereno's team found the wishbone, hipbone, and stomach ribs of the newly found dinosaur species hollowed out—a telltale sign of air sacs [National Geographic News].
In addition to discovering the imprints left by the air sacs, researchers also observed that some of Aerosteon's bones had a sponge-like texture, similar to that seen in birds.
After a bird hatches from its egg, all its bones are solid, like mammal bones, [paleontologist Brooks] Britt said. As the chick grows, its air sacs send out thin strings called "diverticulae" that attach themselves to nearby bones in the skull, spine, femur and shoulder area. The strings find a weak spot, invade the bone interior, and mine out marrow to leave the bones hollow [Chicago Tribune].
The process, called "pneumatization," helps birds reduce their body weight, which makes flight easier. Previously discovered dinosaur fossils have shown evidence of these airy bones, but the newly discovered Aerosteon is the first to complete the picture with evidence of air sacs. In their report, published in the journal PLoS One, researchers speculate on what advantages the dinosaur may have gained from its air sacs and airy bones.
Weighing as much as an elephant, Aerosteon also may have used the openings to shuttle away unwanted heat from its body core, [coauthor Jeffrey] Wilson said. Another advantage of airy bones would be to shed some pounds from the leviathon. "It may have an important functional role in making the backbone light but also strong," Wilson said of the air-sac system. "When you get big, weight is important" [LiveScience].
While most paleontologists agree that birds evolved from dinosaurs, a few skeptics remain. DISCOVER interviewed one of these contrarians, Alan Feduccia, in the article "Plucking Apart the Dino-Birds."
Image: Todd Marshall, courtesy of Project Exploration
