Artwork showing the relative scale of humans and Struthiomimus. This dinosaur's name very aptly means 'ostrich mimic'. They were long-legged theropod dinosaurs that lived during the Late Cretaceous period in North America. Struthiomimus belongs to a diverse group of similar animals called ornithomimids ('bird mimics'). It was a smallish dinosaur, around 4.3 m (14 ft) long, and probably had a substantial covering of primitive feathers