Therizinosaurs were a group of theropod dinsosaurs that are recognized as having long necks, small heads, big claws, and eating plants.
They evolved in the early Cretaceous, although one dinosaur called Eshanosaurus from the early Jurassic of China is suspected to be a therizinosaur. If that is true, than therizinosaurs may have evolved earlier than we thought) and lasted to the K/Pg Extinction.
Therizinosaurs had a very distinctive, often confusing set of characteristics. Their long necks, wide torsos, and hind feet with four toes used in walking resembled prosauropod dinosaurs. Their unique hip bones, which pointed backwards and were partially fused together, initially reminded paleontologists of the "bird-hipped" ornithischians. Among the most striking characteristics of therizinosaurs are the enormous claws on their hands, which reached lengths of three ft. (90 cm.) in Therizinosaurus. The unusual range of motion in therizinosaur forelimbs, which allowed them to reach forward to a degree other theropods could not achieve, also supports the idea that they were mainly herbivorous. Therizinosaurs may have used their long necks and strongly curved claws to grasp and shear leafy branches, in a manner similar to the prehistoric ground sloths. Uniquely among neotheropods, they used all four toes for walking, not just three.
In Walking with... series
Therezinosaurus is the main focus of this episode. This episode shows its' trademark features, including the titular giant claws and its' social life style.