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 set this meat-eater 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 possessed a birdlike respiratory system.
Of course, air-filled bones serve another important function: they help to reduce their owner's overall weight and bulk. That's another thing Aerosteon seems to have had in common with modern birds, whose bones are necessarily light and airy in order to reduce their owner's flying weight. (It's important to bear in mind, however, that modern birds evolved not from one-ton theropods like Aerosteon, but from the small, feathered raptors and "dino-birds" of the late Cretaceous.)