Brontosaurus (/ˌbrɒntɵˈsɔrəs/ bron-tə-SAWR-əs), meaning "thunder lizard" (from Greek βροντή, brontē = thunder + σαυρος, sauros = lizard), is a genus of sauropod dinosaurs. Originally named by its discoverer Othniel Charles Marsh in 1879, Brontosaurus had long been considered a junior synonym of Apatosaurus; its original species Brontosaurus excelsus having been reclassified as A. excelsus in 1903. However, an extensive study published in 2015 by a joint research team of England and Portugal concluded that Brontosaurus was a valid genus of sauropod distinct from Apatosaurus. Nevertheless, not all paleontologists agree with this division.
The same study classified two additional species that had once been considered Apatosaurus as Brontosaurus parvus and Brontosaurus yahnahpin. Species of Brontosaurus range in age from 155 to 152 million years ago, during the Kimmeridgian age of the lower to middle Morrison Formation in Wyoming and Utah, USA.
As the archetypal sauropod, Brontosaurus is one of the best-known dinosaurs, and has been featured in film, advertising, and postal stamps, as well as many other types of media.