O is for Ornithomimus
Ornithomimus was an ornithomimid theropod from the Late Cretaceous of North America, about 70 million years ago. It’s estimated to have reached around 3.8m in length (12’5”). Three specimens have been found with evidence of feathers: a juvenile with hair-like “fuzz”, and two adults with quill knobs on the arm bones. It seems that these dinosaurs developed wing-like feathers at sexual maturity, possibly using them for mating displays similarly to modern ostriches.
The ornithomimids (“bird mimics”) were named for their superficial resemblance to large flightless birds. They had long legs adapted for speed, relatively small heads, and sloth-like arms. They were the most common small dinosaur in North America, suggesting they were probably herbivores — or possibly omnivores supplementing a plant diet with small prey.