Lurdusaurus

Lurdusaurus is one of those dinosaurs that shakes paleontologists out of their complacency. When its remains were discovered in central Africa in 1999, this dinosaur's huge size upset longstanding notions about ornithopod evolution (that is, that the "small" ornithopods of the Jurassic and early Cretaceous periods gradually gave way to the "big" ornithopods, i.e. hadrosaurs, of the late Cretaceous). At 30 feet long and 6 tons, Lurdusaurus (and its equally gigantic sister genus, Lanzhousaurus, which was discovered in China in 2005) approached the bulk of the largest known hadrosaur, Shantungosaurus, which lived 40 million years later.