'Air bone' dinosaur is missing link with birds
Aerosteon riocoloradensis (air bones from the Rio Colorado)
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Tuesday, 30, Sep 2008 03:19
A carnivorous dinosaur with a bird-like breathing system has provided more evidence of the connection between the two groups of animals separated by millions of years.
Palaeontologists from the US have spent the last 12 years examining the fossilised remains of a new dinosaur found in Argentina's Rio Colorado.
They have now concluded that the dinosaur – named as Aerosteon riocoloradensis (air bones from the Rio Colorado) – had air sacs within its body cavity, closely mirroring the breathing systems of birds.
"Among land animals, birds have a unique way of breathing. The lungs actually don't expand," Paul Sereno of the University of Chicago told Public Library of Science ONE.
Instead, birds have developed a system of bellows, or air sacs, which help pump air through the lungs. It is the reason birds can fly higher and faster than bats, which, like all mammals, expand their lungs in a less efficient breathing process.
Aerosteon, a 10m long carnivore that lived 85 million years ago, is part of a lineage that survived in isolation in South America, related to North America's Allosaurus.
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, palaeontologists had found only tantalising evidence in the backbone, outside the cavity with the lungs.
Ricardo Martinez of the San Juan University, which helped with the excavation, commented: "This dinosaur, unlike any other, provides more direct evidence of the bellows involved in bird breathing."
Its bones have telltale pockets and a sponge-like texture called "pneumatisation," in which air sacs from the lung invade bone," Mr Martinez's colleague Oscar Alcober explained. Air-filled bones are the hallmark of the bellows system of breathing in birds.
"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," Mr Alcober added.
Palaeontologists are now satisfied Aerosteon provides 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).