Aerosteon was one of the last true allosaurs. It was a large predator at 25-30 feet long and about 2 tons in weight. Aerosteon seems to have a specialized lung system very similar to that of birds. It suggests that Aerosteon could move quickly and efficiently. Speed estimates average between 20 and 30 miles per hour. Aerosteon lived in South America about 85 million years ago.