Prosauropod and theropod dinosaurs, illustration. The large prosauropod dinosaur (left) is surrounded by four smaller theropod dinosaurs. Prosauropods (now also known as plateosaurids) were sauropodomorphs (long-necked herbivorous dinosaurs) that existed 225 to 203 million years ago, during the Late Triassic. Therapods were bipedal dinosaurs that were initially carnivorous, but later evolved different feeding adaptations. They evolved during the Late Triassic.