Duonychus tsogtbaatari was a therizinosaurid dinosaur living in what is now the Gobi Desert in southern Mongolia during the Late Cretaceous, around 96-90 million years ago.
Like other therizinosaurids it would have been a chunky-bodied herbivore with a small beaked head atop a long neck, long rake-like claws on its hands, stout legs, and a rather short tail. But it was rather small compared to most of its close relatives, estimated at about 3m long (~9'10"), with its known fossil remains including several vertebrae, partial ribs and pelvis, and a set of nearly-complete arms and hands.
Its hands had only two well-developed fingers, with a small splint-like vestigial third finger, an anatomical condition convergently seen in some other theropod groups but previously unknown in therizinosaurids. One of its long curved claws also preserved a rare example of a thick keratinous sheath, showing that in life the claw was over 40% longer than its bony core.
Duonychus' elbow and finger joints had a fairly limited range of motion – more similar to the forearms of Tyrannosaurus than other therizinosaurids – but its claws were able to flex almost 90° at the tips of its fingers, which may have given it the ability to reach out and grab onto foliage with a very strong and precise grip.
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