Mononykus

Mononykus was an unusual, bird-like alvarezsaurid theropod discovered in the Late Cretaceous rocks of the Gobi Desert in Mongolia. About one metre in length, it was roughly the size of a domestic turkey and exhibited an extraordinary anatomy. It possessed long, slender hind legs built for high-speed locomotion, a long tail, and an exceptionally compact forelimb. Instead of grasping hands, each arm ended in a stout, muscular spike bearing a single large thumb claw, while the remaining digits were almost entirely lost. This bizarre apparatus, backed by an enlarged breastbone, was likely adapted for tearing open termite mounds, ant nests, or tree bark in search of insects. Although initially described as a primitive, flightless bird, Mononykus is now understood to be an aberrant, highly modified non-avian coelurosaurian dinosaur.

Its forelimbs were reduced to thick, muscular stumps with a solitary large thumb spike.

Where and when

Mononykus lived in the Late Cretaceous, from 72 to 68 million years ago (Campanian-Maastrichtian age). Its remains come from Mongolia, in the Nemegt Formation.

The numbers

Length 1.1 m (estimates run from 1 to 1.2 m). Mass about 3 kg. Hip height about 0.4 m. That is 0.6 human-lengths, or 0.1 of a double-decker bus. These are estimates from partial skeleton; fields marked estimated by the site are length, mass, first ma, last ma, hip height.

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