Apatosaurus was a massive, long-necked sauropod that roamed North America during the Late Jurassic period, around 152 million years ago. Measuring up to 75 feet long and weighing as much as 22 tons, this giant herbivore used its long neck to reach vegetation high in trees and its powerful tail, possibly as a whip for defense against predators like Allosaurus. Despite its enormous size, Apatosaurus moved on four sturdy legs and likely lived in herds, offering protection through numbers. Often confused with Brontosaurus, Apatosaurus remains one of the most iconic dinosaurs, showcasing the sheer scale of prehistoric life.