It was not until 1992, when the Mongolian-American team discovered more remains of the same animal, that the creature was realized to be something truly odd. In 1993, the Mongolian-American team described the creature in Nature . Superficially, it looked like a small, running dinosaur, with a long, snaky tail, long, spindly legs and a long neck. Although Mononykus looked like an aberrant dinosaur, closer examination revealed a host of bird-like features in the backbone, pelvis and hindlimbs. Controversially, the detailed anatomy of Mononykus looked even more birdlike than that of Archaeopteryx .
Archaeopteryx is famous as the earliest known bird.
It has a long, reptilian tail and jaws with teeth, but its forelimbs are clearly modified into wings, and it had feathers remarkably like those of modern birds. For decades, Archaeopteryx has been seen as a kind of 'missing link' between reptiles and birds, a primitive staging post on the way towards fully modern birds, and fully modern flight. To claim, therefore, that Mononykus was even more closely related to modern birds than Archaeopteryx , even though Mononykus did not have wings and could not have flown, caused a stir among evolutionary biologists. What was lacking from the skeletons of Mononykus found in Mongolia in the early 1990s were good-quality skulls. Although several Cretaceous animals, from South and North America as well as Mongolia, have been recognized as forming a distinctive group of flightless, bird-like dinosaurs, no really good skull material has been described.