Washington, September 30 : The remains of a new 10-meter-long predatory dinosaur discovered along the banks of Argentina's Rio Colorado has revealed that the dino had a bird-like breathing system.
The dinosaur was discovered by paleontologists led by the University of Chicago's Paul Sereno, a National Geographic Explorer-in-Residence.
The discovery of this dinosaur builds on decades of paleontological research indicating that birds evolved from dinosaurs.
"Among land animals, birds have a unique way of breathing. The lungs actually don't expand," Sereno said.
Instead, birds have developed a system of bellows, or air sacs, which help pump air through the lungs. It's the reason birds can fly higher and faster than bats, which, like all mammals, expand their lungs in a less efficient breathing process.
Discovered by Sereno and his colleagues in 1996, the new dinosaur is named Aerosteon riocoloradensis.
Aerosteon, found in rocks dating to the Cretaceous period about 85 million years old, represents a lineage surviving in isolation in South America. Its closest cousin in North American, Allosaurus, had gone extinct millions of years earlier and was replaced by tyrannosaurs.
Laboratory technicians spent years cleaning and CT-scanning the bones, which were embedded in hard rock, to finally reveal the evidence of air sacs within Aerosteon's body cavity.
Previously, paleontologists had found only tantalizing evidence in the backbone, outside the cavity with the lungs.
"This dinosaur, unlike any other, provides more direct evidence of the bellows involved in bird breathing," Martinez said.
Its bones have telltale pockets and a sponge-like texture called "pneumatization," in which air sacs from the lung invade bone. Air-filled bones are the hallmark of the bellows system of breathing in birds.
According to Alcober, "Despite its huge body size and lack of a breastbone or birdlike ribcage, this meat-eater had lungs that already functioned quite a bit like a bird's."
Aerosteon provided the evidence needed to seal the connection with birds - hollow bones in front and behind the ribcage, such as the wishbone (furcula) and the main hip bone (ilium).
Sereno noted that Aerosteon has air sacs in an unusual place.
"They come around the edge of the body and go into belly ribs. It looks like the beast had a system of air tubes under its skin," he said.
The team highlighted three explanations for the evolution of air sacs in dinosaurs in their paper: development of a more efficient lung; reduction of upper body mass in tipsy two-legged runners; and release of excess body heat.