Aerosteon

Aerosteon riocoloradensis from the Late Cretaceous of Argentina. It is known from a partial skeleton (skull reconstruction and images seen on the web [as well as here], are all hypothetical as only a few bits and a tooth have been recovered from the skull). Some of the bones including the furcula, the ilium, vertebrae and the gastralia, show pneumatisation (air-filled spaces) indicating that this theropod might have had air-sac systems allowing them to breathe like modern birds. It also appears to be an allosauroid, a group that so far has never been found in the Gondwanan late Cretaceous.