The prehistoric creature known for its large size and long neck is the dinosaur, specifically the sauropod dinosaurs. Sauropods, such as Brachiosaurus and Apatosaurus, were characterized by their massive bodies, long necks, and long tails. They were herbivorous and roamed the Earth during the Jurassic and Cretaceous periods. Their long necks allowed them to reach high vegetation, making them well-adapted to their environment. These giants could weigh up to 100 tons and could grow over 100 feet in length. Despite their size, their fossils help scientists understand the evolution and diversity of dinosaurs, making them a captivating subject of study.