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mon - oh - NIE - kus
Name Means: "One claw"
Most small theropods had long forelimbs and long, grasping hands. Mononykus and its closest relatives-its fellow alvarezsaurids-are conspicuous exceptions to this rule. Mononykus had very gracile hindlimbs, but its forelimbs were extremely short and its hand was effectively reduced to a single digit-the stout, clawed thumb for which the animal in named. An almost imperceptible second digit is no more than a nubbin.
Mononykus was one of the prizes collected in joint Mongolian-American expeditions to Mongolia undertaken in the mid-1990s. Other alvarezsaurids are known from the Cretaceous of North and South America. It is also possible that members of this family occurred worldwide. Mononykus's forelimbs were too short to be able to reach its face, but they were powerfully built-the construction of the elbows suggests the existence of large extension muscles.
In some ways they resemble the forelimbs of digging animals such as moles. What would a small theropod with graceful legs and a slender body have done with such arms? Might Mononykus have been a digging animal that used its strong, though very short, arms to rip open termire mounds? Perhaps it was, but the rest of the skeleton is absolutely unlike that of any known burrowing animal. The scientists that discovered Mononykus originally thought they had discovered a very primitive bird. It had small teeth and a bony tail, but the breastbone had a small keel and the fibula did not reach to the ankle-features found in birds more advanced than that of Archaeopteryx. However, it is clear that Mononykus was incapable of flight.
Some recent analyses suggest that Mononykus was a very close relative of birds. Others classify it as being closely related to the ornithomimids, such as Gallimimus. Although it seems likely that Mononykus will remain classified as a theropod, its distinctly birdlike features are undeniable. In fact, a recently discovered alvarezsaurid from Mongolia preserves thin fibers that scientists think may be primitive feathers around parts of its body.