Deinocheirus mirificus

This is the largest known Ornithomimosaur, at about 11 meters (36 feet) in length. All that was originally found of this animal was a pair of very large arms and a few ribs. It's identity and biology were much of a mystery for quite a long time, until only very recently has more of the animal been found. This amazing find confirmed its phylogenetic position as an ornithomimosaur, and also reveled that it had extended vertebrae, giving the animal a sail or hump. It was likely a herbivore like the other larger ornithomimosaurs such as Gallimimus and Struthiomimus. It lived at the same time and place as the equally bizarre Therizinosaurus, with whom it may have shared a similar niche.  Deinocheirus was found in the Nemegt Formation in Mongolia, and lived about 70 mya.