|Reconstructed skeleton of Nothronychus|
Therizinosaur fossils have been found in Cretaceous deposits in Mongolia, the People's Republic of China and Western North America. Various features of the forelimbs, skull and pelvis show they are theropods and maniraptorans, close relatives to birds.
Early finds were incomplete, and showed strange anatomy with features typical of theropods, prosauropods and ornithischians. This led some scientists to think that segnosaurs were a late-surviving suborder of primitive dinosaurs.
It was not until the mid-1990s, that their true identity as herbivorous descendants of the carnivorous theropods became generally accepted. Alxasaurus was discovered, and had more typical theropod features; and Therizinosaurus was recognized as a member of the segnosaur group.
The connection between the therizinosaurids and other theropods was made clear when primitive members of the group, such as Beipiaosaurus (1999) and Falcarius (2005) were discovered. The scientists who described Falcarius noted that it seemed to represent an intermediate stage between carnivorous and herbivorous theropods, a sort of "missing link" between predatory maniraptorans and plant-eating therizinosaurs.
- The name therizinosaur is derived from the Greek therizo meaning 'to reap' or 'to cut off' and sauros meaning 'lizard'. The older name segnosaur is derived from Latin segnis meaning 'slow' or 'sluggish' and Greek sauros meaning 'lizard'.
- Paul G.S. 1988. Predatory dinosaurs of the world: a complete illustrated guide. New York: Simon and Schuster. p464
- Russell, D.A.; Dong, Z. (1993). "The affinities of a new theropod from the Alxa Desert, Inner Mongolia, People's Republic of China. In Currie P.J. ed". Results from the Sino-Canadian Dinosaur Project. Canadian Journal of Earth Sciences. 30: 2107–2127.
- Xu, X.; et al. (1999). "A therizinosauroid dinosaur with integumentary structures from China". Nature. 399 (6734): 350–354. doi:10.1038/20670.
- Kirkland, J.I.; et al. (2005). "A primitive therizinosauroid dinosaur from the early Cretaceous of Utah". Nature. 435 (7038): 84–87. doi:10.1038/nature03468. PMID 15875020.