Ornithomimids - The Bird Mimic Dinosaurs

The Evolution and Behavior of Bird Mimic Dinosaurs

gallimimus
Gallimimus, the "chicken mimic," was discovered in the Gobi Desert in 1963 (Sergio Perez).

As dinosaur families go, ornithomimids (Greek for "bird mimics") are a bit misleading: these small-to-medium-sized theropods weren't named for their similarity to flying birds like pigeons and sparrows, but to large, flightless birds like ostriches and emus. In fact, the typical ornithomimid body plan looked a lot like that of a modern ostrich: long legs and tail, a thick, rounded trunk, and a small head perched atop a slender neck.

(See a gallery of pictures and profiles of bird-mimic dinosaurs.)

Because ornithomimids like Ornithomimus and Struthiomimus bear such a marked resemblance to modern ratites (as ostriches and emus are technically classified), there's a strong temptation to infer similarities in the behavior of these two very different types of animals. Paleontologists believe that ornithomimids were the fastest dinosaurs that ever lived, some long-legged varieties (such as Dromiceiomimus) capable of hitting speeds of 50 miles per hour. There's also a strong temptation to picture ornithomimids as covered with feathers, though the evidence for this isn't as strong as for other families of theropods, such as raptors and therizinosaurs.

Ornithomimid Behavior and Habitats

Like a few other dinosaur families that prospered during the Cretaceous period--such as raptors, pachycephalosaurs and ceratopsians--ornithomimids seem to have been confined mainly to North America and Asia, although some specimens have been dug up in Europe, and one controversial genus (Timimus, which was discovered in Australia) may not have been a true ornithomimid at all.

In keeping with the theory that ornithomimids were fast runners, these theropods most likely inhabited ancient plains and lowlands, where their pursuit of prey (or headlong retreat from predators) wouldn't be impeded by thick vegetation.

The most unusual characteristic of ornithomimids was their omnivorous diets.

These were the only theropods we yet know of, besides therizinosaurs, that evolved the ability to eat vegetation as well as meat, as evidenced by the gastroliths found in the fossilized guts of some specimens. (Gastroliths are small stones that some animals swallow in order to help grind up tough plant matter in their guts.) Since later ornithomimids possessed weak, toothless beaks, it's believed that these dinosaurs fed on insects, small lizards and mammals as well as plants. (Interestingly, the earliest ornithomimids--Pelecanimimus and Harpymimus--did have teeth, the former over 200 and the latter a mere dozen.)

Despite what you've seen in movies like Jurassic Park, there's no solid evidence that ornithomimids scurried across the North American plains in vast herds (although hundreds of Gallimimus galloping away from a pack of tyrannosaurs at top speed would certainly have been an impressive sight!) As with many types of dinosaurs, thoughm we know frustratingly little about the daily life of ornithomimids, a state of affairs that may well change with further fossil discoveries.