With its enormous claws, which could reach 70 cm in length, Therizinosaurus looked like a fearsome foe. But this dinosaur was not a deadly predator. Instead, it seems to have survived on a vegetarian diet of leaves and shoots. Its huge claws seem to have been used mainly to strip the foliage from tree branches.
These claws, combined with a long neck and bulbous body, made Therizinosaurus look as if it had been stuck together with bits from other dinosaurs.
It probably roamed the wooded fringe of the Mongolian desert using its long neck to stretch for branches and its long claws to pull them towards its mouth. Therizinosaurus had a large stomach to help it digest all the vegetation it ate.
This dinosaur belonged to the family of dinosaurs called theropods, which includes the meat-eaters Tyrannosaurus and Velociraptor. Therizinosaurus' vegetarian diet made it unusual amongst theropods.
Therizinosaurus' giant claws may also have been used for self-defence or even as part of a mating ritual. In a battle or mating ritual, Therizinosaurus may have stood with its arms outstretched, like a flapping swan, so that it could display the size of its claws. However, its claws were so heavy, Therizinosaurus would probably have folded its arms against its body when it walked.
After mating the female Therizinosaurus laid several eggs in a nest and, like some other Mongolian dinosaurs, may have stayed with the nest until the eggs hatched, helping to rear the young.