Duonychus

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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Erlikosaurus

Erlikosaurus andrewsi, a therizinosaur from the Late Cretaceous of Mongolia (~90 mya).

Named after Erlik, the Turko-Mongolian god of death, it’s only known from partial remains – but it was the first therizinosaur ever found with a preserved skull, helping to fill in some of our knowledge of these oddball dinosaurs’ anatomy.

It was closely related to Therizinosaurus, but was only about half the size, estimated to have measured around 4-5m long (13′-16’4″). It would have had a toothless beak at the front of its jaws, an adaption for a herbivorous diet, along with long claws on its hands and a coat of fluffy down-like feathers. I’ve also given it some longer quill-like feathers here, similar to those known in Beipiaosaurus.