September 30, 2008

Researchers Unearth Dinosaur That Breathed Like A Bird

Paleontologists have discovered the remains of a large meat-eating dinosaur with a breathing apparatus much like a modern bird, fortifying the link between birds and dinosaurs and helping to explain the evolution of birds' unique system of breathing.

The scientists said the specimen, pulled from 85-million-year-old rock along the banks of Rio Colorado in Argentina's Mendoza Province, was a 33-foot-long (10 meter), two-legged predator that weighed as much as an elephant and likely had feathers.

Paul Sereno of the University of Chicago, who wrote about the find on Monday in the journal PLoS ONE, said its method of breathing makes this dinosaur stand out.

Sereno believes instead of lungs that expand and contract, this beast had air sacs that worked like a bellows, blowing air into the beast's stiff lungs, much like modern birds.

"This dinosaur, unlike any other, provides more direct evidence of the bellows involved in bird breathing," said Ricardo Martinez of the Universidad Nacional de San Juan, Argentina, who worked with Sereno on the research.

The researchers named the dinosaur Aerosteon riocoloradensis, meaning "air bones from the Rio Colorado," because its bones have pockets and a sponge-like texture called "pneumatization" in which air sacs from the lung invade the bone.

According to most paleontologists, birds likely evolved from small, feathered meat-eating dinosaurs, and the earliest known birds were strikingly similar to these dinosaurs.

The Aerosteon, a type of dinosaur called a theropod, may have evolved this breathing style in part to keep it from toppling over while chasing prey on its two massive legs. And it may have helped control body temperature.

"If dinosaurs and in particular theropods were 'warm-blooded' as many of us suspect and feathered for insulation, they would have had a major problem getting rid of heat at times. Perhaps this is why air sacs initially evolved, and then were co-opted for breathing," Sereno said.

Aerosteon was smaller than the very biggest meat-eaters, which included North America's Tyrannosaurus rex, Africa's Spinosaurus and Giganotosaurus, also found in Argentina.

Aerosteon represents a separate line of predators that lived alongside and then outlasted Giganotosaurus, Sereno said.

"This is one of the nice surprises of the find."


Image 1: Skull reconstruction of the new meat-eater Aerosteon ("air bones") from Cretaceous-age beds about 85 million years old in Mendoza Province, Argentina. (Photo: Erin Fitzgerald, courtesy of Project Exploration)

Image 2: Flesh rendering of the predator Aerosteon with the body wall removed to show a reconstruction of the lungs (red) and air sacs (other colors) as they might have been in life. (Photo: Todd Marshall, courtesy of Project Exploration)


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