Claosaurus is a genus of primitive hadrosaurid (duck-billed dinosaur) that lived during the Late Cretaceous Period. It had a slender body and slim feet, with long legs, small arms, and a long, stiff tail. It probably grew to a length of about 12 to 16 feet and weighed roughly 1000 pounds. It appears to have walked on its hind legs, dropping to all fours only to graze. Like other hadrosaurs, it was an herbivore. Evidence of its existence was first found near the Smoky Hill River in Kansas, USA in the form of partial skull fragments and as an articulated post-cranial skeleton. Originally named Hadrosaurus agilis (Marsh, 1872), it was placed in a new genus and renamed Claosaurus agilis in 1890 when major differences between this specimen and Hadrosaurus came to light.