Therizinosaurus cheloniformis ("turtle-formed scythe lizard") was a very huge segnosaur (now known as Therizinosaurs). It might grow up to twelve meters (40 feet) long. Therizinosaurus lived in the Late Cretaceous period, approximately 70 million years ago, and its fossils were first exposed in Mongolia. When it was discovered it was originally thought to be a turtle (hence the name cheloniformis - turtle-formed), but it is now conventional as a maniraptoran dinosaur.

Therizinosaurus had a small head, a extended neck, short tail and a large body. Its feet had very bent claws, and its most distinctive feature was gigantic claws on its front limbs (up to nearly a meter, or three feet, in length.)

The feeding habits of Therizinosaurus are still debated, but it was most almost certainly an herbivore, using its big physical claws to push leaves into its mouth. Other hypotheses propose that it was a termite eater, using its claws to open big termite nests, but it seems unlikely that an animal the size of Therizinosaurus could stay alive on a diet based on insects.

There are other likely uses for Therizinosaurus claws, such as defense against predators (such as the contemporary Tarbosaurus) and for intraspecific fight, such as hostility for territory or for mating.

It is likely that Therizinosaurus was feathered, given that its close relation Beipiaosaurus was.