Ornithomimus

MEANING: Bird mimic

PERIOD: Late Cretaceous

CONTINENT: North America

Ornithomimus was a swift runner that superficially resembled an ostrich. It had very long limbs, hollow bones, and a large brain and eyes. Several specimens have been found preserving evidence of feathers, and it had with a small toothless beak that may indicate an omnivorous diet. Ornithomimus was about 4 m in length and 170 kg in weight.

Ornithomimus is from the Late Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Late Cretaceous making up roughly the second half of it, lasting from about 100 to 66 million years ago. It was a time of significant evolutionary change, with dinosaurs reaching their greatest diversity before the mass extinction at the end of the Cretaceous.

The Cretaceous was a period with a relatively warm climate, though the Late Cretaceous experienced a global cooling trend, caused by falling levels of carbon dioxide in the atmosphere. The continents were nearing their present positions, but high sea levels flooded low-lying regions, turning Europe into an archipelago, and forming the Western Interior Seaway in North America. These seas were home to a variety of marine reptiles, including mosasaurs and plesiosaurs, while pterosaurs and birds shared the skies.

On land, dinosaurs continued to thrive and diversify during the Late Cretaceous, producing many of the most well-known goups, including tyrannosaurs, hadrosaurs, and pachycephalosaurs. Established Cretaceous dinosaur clades like the ceratopsians, ankylosaurs, and dromaeosaurs continued to flourish. Sauropod species consisted almost exclusively of titanosaurs, which seemed to be confined to the Southern Hemisphere for much of the Late Cretaceous. Flowering plants and grasses diversified and spread, becoming the dominant flora similar to what we see today.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene (K–Pg) extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. This event, likely triggered by an asteroid impact, is marked by the abrupt K–Pg boundary, a distinct geologic layer separating the Mesozoic and Cenozoic Eras. In its aftermath, mammals and avian dinosaurs rapidly diversified, becoming the dominant land animals of the Cenozoic Era.

Ornithomimus is an ornithomimosaur. Ornithomimosaurs are omnivorous theropods from the Cretaceous Period. They mostly resemble modern-day ostriches, as fast runners with long legs and long necks. However, this group also contains the Deinocheirids, which were much bulkier and more robust. The group first appeared in the Early Cretaceous and persisted until the end of Late Cretaceous.

The skulls of ornithomimosaurs were mostly small, with large eyes, above relatively long and slender necks. The most basal members had a jaw with small teeth, while the later and more derived species had a toothless beak. The arms were long with powerful claws. Evidence of feathers is known from some specimens, and ornithomimosaurs are mostly speculated to have been covered in ostrich-like plumage.