Size and Weight:
In most ways, Aerosteon was a typical predatory dinosaur of the late Cretaceous period, with its classic theropod shape (powerful legs, short arms, bipedal stance) and sharp teeth. What sets this theropod apart from the pack is the evidence of air sacs in its bones, which globetrotting paleontologist Paul Sereno has taken as evidence that Aerosteon (and, by implication, other theropods of its kind) may have had a birdlike respiratory system.
Of course, air-filled bones serve another important function: they help to reduce a creature's overall weight and bulk. That's another thing Aerosteon may have had in common with modern birds, whose bones are necessarily light and airy in order to reduce their owner's flying weight (in any event, prehistoric birds almost certainly evolved from theropod dinosaurs!).