Picture of mononykus olecranus dinosaur

Mononykus olecranus was a peculiar dinosaur with very strong—and very short—arms, each of which had only one finger.

Image © National Geographic Society

Fast Facts

3 ft (1 m) long
Did you know?
Mononykus's muscle-bound elbow reveals that its stubby arms were extremely powerful.
Size relative to a 6-ft (2-m) man

Please add a "relative" entry to your dictionary.

Mononykus olecranus is a rather strange dinosaur that has perplexed scientists and resisted a definitive classification.

Mononykus's most distinctive feature is a pair of short, stunted forelimbs, each of which had only one functional finger and claw. The strange physiology of these short limbs has given rise to several competing hypotheses about the ancient animal's behavior.

The small limbs' orientation may have made them useless for snatching prey or digging burrows. They may have been used to dig into nests of insects or to rend plants for digestion.

But some scientists believe that the unusual arms were used to hook and pull ants from their lairs in much the same manner used by some modern anteaters or pangolins. These animals also feature a single digit and elongated claw. This would be a rather unusual behavior for a dinosaur since most others were either confirmed vegetarians or formidable predators.

Still other researchers have suggested that Mononykus was not a birdlike dinosaur at all but an ancient, flightless bird. This interpretation arises because of a keel, or ridge, that runs down the animal's sternum, which is like that found in many birds.

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