Apatosaurus (ah-pah-tuh-SORE-uss) was one of the biggest dinosaurs that ever lived. It was as long as a basketball court! It may have weighed as much as forty tons. This giant herbivore lived about 150 million years ago in the Jurassic period.
Apatosaurus walked on four legs that were as big as tree trunks. Each leg was taller than a man. It had a long, thin neck and an even longer tail that was used like a whip. One thing about Apatosaurus wasn't big. Its brain was only about the size of an orange! Its head looked too small for its gigantic body.