Therizinosaurus is an extinct genus of the therizinosaurid family that lived in Mongolia during the Late Cretaceous period around 70 million years ago.

The appearance of Therizinosaurus had been a debate until recent decades because of the highly incomplete nature of early finds and a lack of knowledge of the dinosaurs that would come to be categorized later as therizinosauridae. During the early phases of its discovery, it was assumed to be a species of an aquatic turtle. After several examinations and revisions, it was given the description of a gigantic carnosaur (at the time, a family that included most large carnivorous dinosaurs) measuring 55 ft in length. After the discovery of related species Nothronychus, the debate over its appearance ended. While its diet remains unconfirmed, Therizinosaurus was originally thought to be a carnivore, at the point when it was incorrectly theorized to be a much larger animal with a radically different body plan. However, today, scientists agree that Therizinosaurus was not carnivorous, instead being herbivorous, based on studies of its close relatives like Erlikosaurus, Segnosaurus, Nothronychus, and Falcarius. Based on studies of its relatives, Therizinosaurus is believed to have had weak jaws and probably would have fed by sitting down and using its long arms and claws to pull vegetation into its mouth, but these claws are also believed to also be used to defend itself as well. Footprints suggested to have come from unknown therizinosaurids suggest it may have had a plantigrade walking stance, similar to bears and crocodiles. It remains unknown whether paleontologists will find a complete fossil and skull of Therizinosaurus in the near future.