Ornithomimids convergently evolved a body plan startlingly close to modern ratites: long, slender legs for running, a long flexible neck, a small toothless head with a beak, and large eyes suggesting keen vision. Diet is thought to have ranged from omnivorous to largely herbivorous depending on the genus, a departure from the strictly carnivorous diet typical of most theropods, aided by the loss of teeth in favor of a beak.
The family is well represented across Cretaceous North America and Asia. Struthiomimus and Ornithomimus, both North American, and Gallimimus, from Mongolia -- discovered in part through Zofia Kielan-Jaworowska's Polish-Mongolian expeditions -- are among the best-known genera, and their build made them likely among the fastest-running dinosaurs of their ecosystems.