Ornithomimosaurs (meaning 'bir mimic lizards') or members of the clade Ornithomimosauria are theropod dinosaurs, like Gallimimus, which bore a superficial resemblance to modern ostriches. They were fast, fleet-footed, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia (now Asia, Europe and North America). The group first appeared in the Early Cretaceous and persisted until the Late Cretaceous. They appear to be related to less-derived coelurosaurian theropods such as Compsognathus and tyrannosaurids. Primitive members of the group include Pelecanimimus, Shenzhousaurus, Harpymimus and probably the huge Deinocheirus, the arms of which reached eight feet (2.4m) in length. More advanced species, members of the family ornithomimidae, include Gallimimus, Archaeornithomimus, Anserimimus, Struthiomimus, and Ornithomimus. Some paleontologists, like Paul Sereno, consider the enigmatic alvarezsaurids to be close relatives of the ornithomimosaurs and place them together in the superfamily Ornithomimoidea (see classification below).