Apatosaurus opponent of Marsh and his taxa, labeled the "Apatosaurus" mount of the American Museum of Natural History "Brontosaurus". Because of this decision the name "Brontosaurus" was commonly used outside of scientific literature for what Riggs considered "Apatosaurus", and the museum's popularity meant that "Brontosaurus" became one of the best known dinosaurs, even though it was invalid throughout nearly all of the 20th and early 21st centuries. It was not until 1909 that an "Apatosaurus" skull was found during the first expedition, led by Earl Douglass, to what would become known as the Carnegie Quarry at Dinosaur National Monument. The skull
Apatosaurus names; he grouped "Apatosaurus" within Opisthocoelia. Sauropoda is still used as the group name. In 2011, John Whitlock published a study that placed "Apatosaurus" a more basal diplodocid, sometimes less basal than "Supersaurus". Cladogram of the Diplodocidae after Tschopp, Mateus, and Benson (2015). It was believed throughout the 19th and early 20th centuries that sauropods like "Apatosaurus" were too massive to support their own weight on dry land. It was theorized that they lived partly submerged in water, perhaps in swamps. More recent findings do not support this; sauropods are now thought to have been fully terrestrial animals. A study