Apatosaurus (which used to be known as Brontosaurus) was one of the largest land animals that ever existed. Apatosaurus lived during the late Jurassic Period, about 157-146 million years ago.

Anatomy: Apatosaurus was a long-necked, whip-tailed dinosaur. It measured about 70-90 feet long (21-27 m) and about 15 feet (4.6 m) tall at the hips. Its head was less than 2 feet long; it had a long skull and a very tiny brain. This plant-eater had a long neck (with 15 vertebrae), a long whip-like tail (about 50 ft = 15 m long), a hollow backbone, peg-like teeth in the front of the jaws, and four massive, column-like legs. Its hind legs were larger than the front legs. Apatosaurus' nostrils were located on the top of its head.

Fossils: Many fossils of Apatosaurus have been found in Colorado, Oklahoma, Utah, and Wyoming, in the USA.

Name: The American paleontologist Othniel C. Marsh described and named Apatosaurus in 1877. A few years later, in 1879, he described and named another fossil, Brontosaurus. It turned out that the two dinosaurs were actually two species of the same genus. The earlier scientific name, Apatosaurus, was adopted.