Coelurus (meaning "hollow") is a poorly known genus. It was perhaps a bipedal theropod dinosaur 6 feet (1.8 m) long, weighing roughly 20 kg. Its femur (thigh bone) was 55 cm long. It was a carnivore that lived during the late Jurassic period, about 156 to 145 million years ago. Its bones were hollow and lightweight, so "Coelurus" was probably light and fast. Its fossils were found in Wyoming. "Coelurus" was named by paleontologist Othniel C. Marsh in 1879.