Apatosaurus, formerly known as Brontosaurus, is a genus of sauropod dinosaur that lived during the Late Jurassic period, approximately 150 million years ago. It was one of the largest land animals to have ever existed, reaching lengths of up to 75 feet (23 meters) and weighing up to 38 tons.

Apatosaurus had a long neck and tail, a small head, and a massive body supported by four sturdy legs. Its neck, which measured around 25 feet (7.6 meters) in length, was used for reaching vegetation high above the ground. It had a long, whip-like tail that could have been used for defense and balance.

Contrary to earlier beliefs, Apatosaurus was a terrestrial dinosaur that lived on land, not in water. It had strong, column-like legs and is thought to have moved relatively slowly. Its diet consisted mainly of plants, including ferns, cycads, and conifers. It would have used its sharp teeth and powerful jaws to strip leaves and twigs from trees.

One interesting feature of Apatosaurus is its long neck vertebrae, which contained hollow chambers filled with air sacs. This adaptive feature, known as pneumaticity, helped reduce the weight of its massive body and made movement more efficient. It is believed that Apatosaurus may have had a counterbalancing system in its tail to help support its massive neck.

The name Apatosaurus means “deceptive lizard” because the first fossils discovered were initially thought to belong to a different dinosaur species. Later, it was realized that these fossils were from the same animal as the previously named Brontosaurus. However, the name Brontosaurus is still sometimes used informally to refer to Apatosaurus.

Overall, Apatosaurus was an impressive and fascinating dinosaur, representing the awe-inspiring diversity of life that existed on Earth millions of years ago.