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."
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).
Said co-author of the PLoS ONE article Jeffrey Wilson of the 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."
Sereno further 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.
Sereno is especially intrigued by heat loss, given that Aerosteon was likely a high-energy predator with feathers but without sweat glands as in birds. At approximately 30 feet in length and weighing as much as an elephant, Aerosteon might well have used an air system under the skin to rid itself of unwanted heat.
|Contact: Steve Koppes|
University of Chicago