Aerosteon

Aerosteon is an extinct genus of tetanuran theropod dinosaur from the Late Cretaceous period of Argentina. Its remains were discovered in 1996 in the province of Mendoza. They show evidence of a bird-like respiratory system. Aerosteon's name can be translated as air bone and derives from Greek ἀήρ (aer, "air") and οστέον (osteon, "bone").

Description


Aerosteon was a 9 metre (30 ft) long bipedal carnivorous dinosaur that lived approximately 84 million years ago during the Santonian stage.

The remains discovered include a single tooth, some cranial bones, a number of partial or complete vertebrae from the neck, back, and sacrum, several cervical and dorsal ribs, gastralia, furcula (wishbone), left scapulocoracoid, left ilium, and left and right pubes. The incomplete fusion of some of its bones indicate that it was not quite fully mature.

Aerosteon does not appear to belong to any of the three groups of large theropods that are known to have inhabited the southern continents during this time (cf. Abelisauridae, Carcharodontosauridae, Spinosauridae). It may represent a new group or be a late-surviving basal tetanuran. Sereno has suggested that it might be related to the Allosauroid radiation of the Jurassic period.

The type species and only known species is A. riocoloradensis. Its specific name indicates that its remains were found in the Rio Colorado Formation.

Physiology
Some of Aerosteon's bones show pneumatisation (air-filled spaces), including pneumatic hollowing of the furcula and ilium, and pneumatisation of several gastralia, suggesting that it may have had a respiratory air-sac system similar to that of modern birds. These air sacs would have acted like bellows, moving air into and out of the animal's relatively inflexible lungs, instead of the lungs being expanded and contracted as occurs with mammals. See avian respiratory system for more detailed information on this.

Sereno theorises that this respiratory system may have developed to assist with regulating body temperature and was later co-opted for breathing.