Mononykus (single claw, so named for its single digit fore-limbs) is amazingly closely related to birds, and yet, is still a theropod dinosaur. It roamed open desert plains, and, because of its light, hollow bones, fossil specimens are frustratingly incomplete. It had large, keen eyes, and, as such, is likely to have been (at least) partially nocturnal. It had strong legs, making it a swift predator, and it likely fed on plants as well as lizards and insects. Those arms! That finger! What could they have been used for? Paleontologists speculate that Mononykus used those surprisingly muscular arms and fingers to break open termite mounds in search of food, rather than for snatching prey or digging.