Meat-eating dinosaur helps unravel how birds evolved breathing system

Washington, Sep 30 (IANS) The remains of a big predatory dinosaur, discovered along Rio Colorado river banks in Argentina, is helping to unravel how birds evolved their unusual breathing system.

The discovery by University of Chicago's Paul Sereno, a National Geographic explorer-in-residence and his team, builds on decades of paleontological research indicating that birds evolved from dinosaurs.

Joining Sereno to announce the discovery at a news conference in Mendoza, Argentina on Monday were Ricardo Martinez and Oscar Alcober, both of the Universidad Nacional de San Juan, Argentina.'

'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 in 1996, the new dinosaur is named Aerosteon riocoloradensis or 'air bones from the Rio Colorado.' '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.

The University of Chicago press release said lab 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 tantalising 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.

Alcober noted: '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.'

Said co-author of the study Jeffrey Wilson University of Michigan: 'The ancient history of features like air sacs is full of surprising turns, the explanations for which must account for their presence in a huge predator like Aerosteon as well as in a chicken.'

These findings were published on Monday in the online version of the Public Library of Science ONE.