Therizinosaurus (Greek for "reaping lizard"); pronounced THER-ih-ZINE-oh-SORE-us
Woodlands of Asia
Late Cretaceous (80-70 million years ago)
Size and Weight:
About 35 feet long and 3 tons
Extremely long arms with two-foot-long claws
There's nothing like an assortment of weird anatomical details--claws the length of human arms, a beaked skull set atop a long neck, a pot belly and a bipedal stance--to fire the imagination of dinosaur artists. Therizinosaurus has been depicted as sporting everything from Big Bird-like feathers to alien-looking black-and-green stripes, but as is often the case with dinosaurs, we may never know for sure how it really looked. Fitting its unique appearance, this dinosaur has given its name to a whole family of bizarre reptiles, the therizinosaurs.
Why did Therizinosaurus have such long claws? It seems unlikely that they were used for hunting, since weapons this huge and blunt would be ineffective in combat (and in any case, this dinosaur was almost certainly a vegetarian). Today, most paleontologists believe Therizinosaurus used its claws to scale trees and collect fruits and leaves, much like a modern sloth. It's also possible that the claws were a sexual adaptation, that is, males with longer, more noticeable claws has more of an opportunity to mate with females (or vice-versa).
Technically, Therizinosaurus was a late Cretaceous theropod, an extensive family of (mostly) carnivorous dinosaurs that also included tyrannosaurs and raptors. What set the therizinosaurs (and two other groups of theropod dinosaurs, the ornithomimids and oviraptors) apart from the rest of their breed is the possibility that some of them may have been exclusive herbivores, a far cry from the standard theropod diet of frightened animals. (By the way, although most therizinosaurs hailed from Asia, at least two genera, Nothronychus and Falcarius, were native to North America.)