Apatosaurus

Apatosaurus is a genus of large sauropod dinosaurs that lived in North America during the Late Jurassic period, roughly 152 to 151 million years ago. It is one of the best-known fossil dinosaurs and a representative example of the long-necked, long-tailed herbivores that dominated terrestrial ecosystems at the time.

Apatosaurus was a quadrupedal herbivore with a massive body carried on four sturdy pillars. It had a relatively small skull and long neck and tail, with the forelimbs slightly shorter than the hind limbs. Its size and skeletal features indicate a animal built for grazing vegetation over a wide area. Length estimates commonly fall around 20 to 23 meters (about 65 to 75 feet), with weights in the range of 20 to 30 metric tons.

In terms of discovery and classification, Apatosaurus was first described by Othniel Charles Marsh in the late 19th century. The name Brontosaurus appeared in subsequent years for related fossils, but for much of the 20th century Brontosaurus was treated as a synonym of Apatosaurus. Some modern studies have revived Brontosaurus as a separate genus, though this view is not universally accepted and many sources continue to use Apatosaurus as the valid name for the well-known specimens.

Fossils of Apatosaurus are primarily found in the Morrison Formation, a rich Late Jurassic deposit. The genus has played a key role in discussions of sauropod gigantism and the evolution of extremely long-necked herbivores.