Several dinosaurs were beaked, including the herbivorous Triceratops and Stegosaurus. Ornithomimosaurs were the only meat eaters to evolve beaks.
One of the best known ornithomimosaurs was Struthiomimus, an omnivore that enjoyed a rounded diet of vegetation and small animal fare, including eggs and insects. This nimble creature was 3–4 meters long, stood 2 meters tall, and weighed 140 kg.
The whole group is commonly called ostrich dinosaurs, though the similarity is only an example of parallel evolution, as these theropods were not related to emergent birds. Convergence included beaks without teeth: an avian feature. Early ornithomimosaurs had tiny teeth, as did nascent birds. This trait wore away as adaptation progressed in later species.
Ornithomimosaurs were ground-bound, with long tails. This tail distinguishes these dinosaurs from all birds, ostriches included.
The lifestyle of ornithomimosaurs was quite like ostriches, which are an omnivorous flightless bird. Like ostriches, when in danger, their response was to run. Ornithomimosaurs were likely the fleetest of all dinosaurs. Some were faster than ostriches, which can run 80 km/hr.
Ornithomimosaurs emerged in the Late Cretaceous: one of the last dinosaur groups to appear. Their continuing evolution was apparent as the reign of dinosaurs ended.