Mononykus was a small, birdlike animal with unusual arms. Its number of fingers was reduced to a single, massively-clawed digit. Its arms were extensively muscled, as evidenced by massive muscle attachment sites on its elbows. Despite their high degree of development, the forelimbs of Mononykus are relatively small in proportion to its body. When faced with so many unusual features concentrated in such a small part of an animal's anatomy, it is tempting to ask, what were they for?

Robust claws and heavily muscled forelimbs are often associated with fossorial or digging animals. The size and position of Mononykus forelimbs seem to preclude their use for digging extensive tunnels for this animal to travel through, although they might be an adaptation for digging small areas for specific food items, such as roots from the ground or insects from tree bark. The heavily-clawed forelimbs might have been used for sparring and/or grappling during mating or disputes. Or they may just be the reduced version of a larger forelimb used for a more specific function by an unknown ancestor.

Ultimately, we may never know what the forelimbs were used for, and even if a plausible use were suggested, it could never be proven conclusively. Some scientists actively avoid engaging in such speculation, considering them to be "just-so-stories" that distract us from questions that can be tested, such as ananimal's relationships. Ultimately, the HMNH feels that the true charm of the extinct lies in their openness to interpretation, and we simultaneously accept the futility of paleobiological speculation while cherishing and exploiting the idle thoughts that stony old bones inspire.