What is Therizinosauria?

The most inclusive clade containing Therizinosaurus cheloniformis but not Tyrannosaurus rex, Ornithomimus edmontonicus, Mononykus olecranus, Oviraptor philoceratops and Troodon formosus. Therizinosaurs (members of Therizinosauria) are a strange-looking bunch who have caused nothing but headaches, from a classification viewpoint. They have a backward facing pubis like ornithischians, a long neck, small head, small teeth, and four-toed hind feet like non sauropod sauropodomorphs (prosauropods), huge hand claws suggestive of the primarily carnivorous branch of saurischian dinosaurs known as theropods, and have, unsurprisingly, been plonked in all three groups by various experts since their remains were first discovered over 60 years ago. They have some weird features all of their own too, like wide, flared out hips to support a huge pot belly, but the presence of a specialized half-moon shaped bone (the semi-lunate carpal), which affords the wrist increased mobility, betrays their true identity. Therizinosaurs are maniraptoran theropods, but maniraptorans with a difference; they were too fat to run and mostly hunted plants, which is why they're known informally as "sloth dinosaurs". Therizinosauria is derived from the Greek "therizo" (to reap or cut with a scythe), "sauros" (lizard), and "-ia" (neuter plural), named for a group of mostly herbivorous (or possibly omnivorous) dinosaurs with long, scythe-shaped hand claws.