Were dinosaurs herbivores, carnivores or both?

There are two main groups of dinosaurs: (1) saurischians, which include the meat-eating (carnivore) theropods such as T.rex and the gigantic plant-eating (herbivore) sauropodomorphs such as Diplodocus; and (2) ornithischians all of which were plant-eaters (these include animals such as the stegosaurs, ankylosaurs, ceratopians and ornithopods). A few rare examples among the theropods, which were for the most part meat-eaters - lack teeth and had a bird-like beak; it is thought that these animals, which were rather similar to ostriches today may have had a similar diet, eating insects and lizards as well as fruit, seeds and leaves (omnivores, eating both meat and plants).