Omeisaurus is a genus of dinosaur belonging to the family Mamenchisauridae. It thrived during the Middle Jurassic, approximately 165 to 160 million years ago, in what is now present-day China. The first fossils of Omeisaurus were discovered in the 1930s in the Sichuan Province, providing paleontologists with insights into this dinosaur.

Omeisaurus was a large-sized dinosaur, estimated to have reached lengths of up to 15 to 20 meters. It possessed a long neck, a characteristic feature of sauropod dinosaurs, along with a comparatively small head and a robust body. Its forelimbs were shorter than its hind limbs, and it walked on all four legs. The neck alone could measure up to 8 meters in length, allowing Omeisaurus to reach vegetation at great heights.

Omeisaurus is believed to have been a gregarious dinosaur, forming herds that provided protection against predators and facilitated foraging efficiency. Its long neck allowed it to access high vegetation, reducing competition with other herbivores. Omeisaurus likely had a slow and deliberate movement, relying on its size and group dynamics for defense against potential threats.