Deinonychus was a lightly built, fast-moving, agile, bipedal (walked on two legs), bird-like dinosaur. It was built to kill. This meat-eater had a curved, flexible neck and a big head with sharp, serrated teeth in very powerful jaws. Each of its three fingers on each hand had large, sharp, curved claws. It had four-toed feet; the second toe had a 5-inch sickle-like claw, and the other toes had smaller claws. Its long tail had bony rods running along the spine, giving it rigidity; the tail was used for balance and fast turning ability. Deinonychus had a relatively large brain and large, keen eyes. Deinonychus was about 10 feet long, 5 feet tall, and weighed up to 80 kg.