Aerosteon, meaning “air bone”, is a genus of theropod dinosaur from the Santonian age of the Late Cretaceous Period (84 million years ago). It lived in what is now Argentina. It was discovered in 1996 in the province of Mendoza. The type, and only known, species is A. riocoloradensis. Its specific name refers to the Rio Colorado Formation where it was found.

Aerosteon is known from a single tooth, some cranial bones, partial vertebrae from the neck, back, and sacrum, some ribs, and various other bones. The incomplete fusion of some of the bones indicate that it was not a fully grown dinosaur. There was also evidence it had a bird-like respiratory system. It may have had a respiratory air-sac system that would have worked like a bellows, moving air into and out of the animal’s inflexible lungs. Some theorize that the system may have developed first to assist with regulating body temperature.

Aerosteon does not appear to belong to any of the three main groups of large theropods that are known to have lived on the southern continents during the Santonian age. It may represent a new group or be a late-survivor from the previous age. It may have some relationship to the allosaurids of the Jurassic era.

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