Othnielia was discovered and named after Othniel Charles Marsh in 1977 by Galton. Othnielia lived in Colorado, Utah, and Wyoming during the Late Jurassic, 156 - 145 million years ago.
Othnielia was 1.5 - 2 meters (4.9 - 6.6 feet) long on average, but could reach up to 2.4 - 2.7 meters (8 - 9 feet) long, weighing in at 79.4 kg (175 lbs).
Othnielia was similar to Hypsilophodon, but its vertebrae had a different shape and the toes of the hind foot were slimmer. Othnielia was bipedal with powerful thigh muscles and a tail that was rigid with numerous bony tendons that where attached to the tail vertebrae. It was likely a fast runner, but no calculations have been published as of yet.