Ornitholestes (Or-nith-oh-LES-teez) was a carnivore that walked on two long legs, was lightly built, and must have been a very fast runner. It had a small head, a small bony crest on its long snout, many sharp teeth, an s-shaped neck, and a long, tapered tail.

Its arms were short and strong; it had long, clawed, four-fingered hands (one finger of which was tiny). Its long tail was probably used for balance and agility, allowing this predator to change directions quickly as it chased prey. Ornitholestes was about 6.5 feet (2 metres) long (from snout to tail) and weighed roughly 25 pounds (12 kg).

Ornitholestes lived in the late Jurassic period, about 156-145 million years ago. Ornitholestes was a carnivore, a meat eater. It may also have been a scavenger. It may have hunted the newly evolved Jurassic period birds. Slightly built and long legged, Ornitholestes was a very fast bipedal runner. Dinosaur speeds are estimated using their morphology (characteristics like leg length and estimated body mass) and fossilized trackways.

Ornitholestes fossils have been found in Wyoming and Utah, USA. Ornitholestes was first described and named by the US paleontologist Henry F. Osborn in 1903.