Tuesday, September 30, 2008

Did Dinosaurs Breathe Like Birds?

When I was growing up, the relationship between dinosaurs and birds was tenuous at best. The concept of swift and warm-blooded dinosaurs was hotly contested, and most illustrations depicted Tyrannosaurus Rex as a slow, sluggish, tail-dragging reptile chasing after equally ponderous herbivores. Scientists now theorize that dinosaurs were much faster than previously thought; that Tyrannosaurus Rex carried its tail horizontally to counterbalance its body as it chased after prey; and that many dinosaurs, especially dromaeosaurs (raptors) might have had primitive feathers. The evidence linking birds to dinosaurs is now so overwhelming that some researchers have taken to classifying birds as living members of the dinosaur family.

A recent excavation in Argentina adds yet more weight to the dinosauria-avis connection. Paleontologists from the USA, Canada, and Argentina recently exhumed the fossilized remains of an Aerosteon riocoloradensis, a newly-discovered carnivorous dinosaur from the Cretaceous period. This particular fossil displays a trait that paleontologists in support of the dinosaurian birds theory have been hoping for: a network of air-filled cavities inside the animal's bones.

Modern-day birds stay aloft in part thanks to a specialized system of air sacks distributed throughout their bodies. These sacks act like a bellows, pumping air in and out of a rigid lung rather than relying on a diaphragm to expand and contract the chest cavity. Air cycles through pneumatic chambers inside of bone, giving the animal more loft and keeping them lightweight. The hollow chambers inside of Aerosteon's bones suggest that it, too, might have had a system of air sacks throughout its body.

In addition, several ribs bear the imprint of what could be air sacks. Because of the air sacks' structure, finding the imprints of them on fossilized bone is a welcome stroke of luck for the international team responsible for Aerosteon's discovery.

If the theories regarding this dinosaur's pneumatic bones and imprinted ribs prove true, it will lend yet more weight to the idea that birds are simply highly evolved dinosaurs. The one drawback to this is that it will only further the exploits of researchers attempting to reverse-engineer raptors from emus.

Classifying birds as modern-day dinosaurs is fine, but does the world really need an emu with teeth?