The Apatosaurus was a large, long-necked dinosaur that lived during the late Jurassic period, around 150 million years ago. It belonged to a group called sauropods, known for their massive size and herbivorous diet. Apatosaurus could grow up to 75 feet long and weighed around 20 tons, making it one of the largest land animals of its time. Apatosaurus had a long, whip-like tail and a small head relative to its body. Its neck was long enough to reach high vegetation, allowing it to feed on leaves and plants. This dinosaur is often confused with its close relative, Brontosaurus, due to similar features and historical naming controversies.