Longest arms for a bipedal dinosaur

The bipedal dinosaur (dinosaur walking on its hind legs) with the longest arms was Deinocheirus mirificus. Its arms measured 2.4 m long, and each hand bore three large-clawed fingers. A species of ornithomimosaur or ostrich dinosaur, so-called because it was superficially similar in form to an ostrich, it lived approximately 71–69 million years ago during the late Cretaceous in what is today Mongolia. The maniraptoran dinosaur Therizinosaurus cheloniformis also had very long arms, and some researchers have estimated that in some specimens they may have attained a length of up to 3.5 m, but no examples measuring this length have so far been uncovered, and as it is only known from very incomplete remains there is no certainty as yet that it was habitually (if indeed at all) bipedal.

Deinocheirus mirificus first became known to science in 1965 with the discovery of a pair of huge fossil arms and shoulder girdles in Mongolia's Nemegt Formation, but no further remains were discovered for almost 50 years. In 2014, however, two much more complete specimens were described, enabling its taxonomic affinities to be determined, and revealing that its hind limbs were rather short, and its backbone bore a sail.