Mononykus was first unearthed in Mongolia in 1923. However, it was not until 70 more years that it was recognized as a unique and unusual dinosaur. It lived 70 million years ago, at the same time and place as Velociraptor. It was a small dinosaur, only 3 feet (1meter) long. Mononykus has a light skeleton, an elongated tail and slender legs. Most striking of all is its unusually short forelimbs. It had remnants of two claws and one large one. The big claw is disproportionately large and robust for that of a sole finger. Phalange (finger bone), ulna (lower arm bone) and humerus (upper arm bone) are all similar in length. The keeled sternum of Mononykus  seems to have supported heavy muscles. Digging animals, like moles, also have short arms with large muscle attachment area, but the long slender hind legs and long flexible neck would have made it unsuitable for mole-like digging. The function of the highly specialized arms is still a mystery, but some scientists have suggested they were used to break open termite mounds (like modern anteaters), and therefore it is possible that they fed primarily on insects.
    Mononykus has a small, keeled sternum and a reduce lower end of the fibula. These are two features that are found in modern birds. This has led to Mononykus being described as a primitive bird, however, its forelimbs are in no way similar to the avian wings.