Therizinosaurus has been an intriguing puzzle for scientists ever since several huge claws were first discovered in 1948. Although there was not enough fossil material to determine its appearance, the claws were so unique that they had to be from a new species. Maleev named it Therizinosaurus cheloniformis in 1954.

Around ten years later another large claw was found, but this time along with other fossils, including a tooth, parts of the front and rear limbs and even a four-toed foot. They gave paleontologists enough material to get a fairly good idea of the animal's body. No skull had yet been found to provide material for head reconstruction.

A series of finds in Mongolia in the late 1980?s showed that huge arms that had been previously attributed to Deinocheirus, actually belonged to the same group as the huge claws and strange bones attributed to Therizinosaurus. Parts of the pelvis and other bones were also found, which gave paleontologists an even better look at what was shaping up to be the strangest dinosaur ever to walk the earth.

Therizinosaurus had a small head, a long neck, short tail and a large body. It was so bulky that it could not have been a very fast runner. Its most distinctive feature was gigantic claws on its front limbs. They were nearly three feet long. The feeding habits of Therizinosaurus are still debated, but it was most probably an herbivore, using its big manual claws to push leaves into its mouth.

While the claws were very long, they were not sharply curved. In cross section, they were quite thin. Some scientists think they were used to tear open termite mounds. Therizinosaurs had a fairly long neck, small head, and teeth that could have been used to eat plants. The family previously known as segnosaurs is now named after this peculiar dinosaur.