Ornithomimidae

Anserimimus
Archaeornithomimus
Deinocheirus  ?
Dromiceiomimus
Gallimimus
Ornithomimus
Struthiomimus

Ornithomimids ("Ostrich mimics") or members of the Ornithomimidae family are theropod dinosaurs, like Gallimimus. They were fast, fleet-footed, omnivorous and herbivorous dinosaurs from the Upper Cretaceous of Laurasia (Asia, Europe and North America). The skull, sitting atop a long neck, was relatively small with large eyes. Some primitive species had teeth, but most had toothless beaks. The arms were long and slender and bore powerful claws. The limbs were long and powerful, with a long foot and short, strong toes terminating in hooflike claws. Ornithomimids were probably among the fastest of all dinosaurs. Like many other coelurosaurs, the ornithomimid hide was probably feathered rather than scaly.

The group first appears in the Lower Cretaceous and persisted until the Upper Cretaceous. They appear to be related to less derived coelurosaurian theropods such as Compsognathus and tyrannosaurids. Primitive members of the family include Pelecanimimus and Harpymimus . More advanced ornithomimids include Gallimimus, Archaeornithomimus , Anserimimus, Struthiomimus , Ornithomimus and probably the huge Deinocheirus , whose arms reached eight feet in length.

Ornithomimids probably got most of their calories from plants but may have eaten small vertebrates and insects as well. Henry Fairfield Osborn suggested that the long, sloth-like arms may have been used to pull down branches for ornithomimids to feed on; it may also have been a dangerous weapon. The sheer abundance of ornithomimids — they are the most common small dinosaurs in North America — is consistent with the idea that they were plant eaters, as herbivores usually outnumber carnivores in an ecosystem. The presence of gastroliths in the stomach of some ornithomimids fits this hypothesis.