Allosaurus fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphans, several species of pterosaur, numerous dinosaur species, and early mammals such as docodonts, multituberculates, symmetrodonts, and triconodonts. Dinosaurs known from the Morrison include the theropods "Ceratosaurus", "Ornitholestes", "Tanycolagreus", and "Torvosaurus", the sauropods "Haplocanthosaurus", "Camarasaurus", "Cathetosaurus", "Brachiosaurus", "Suuwassea", "Apatosaurus", "Brontosaurus", "Barosaurus", "Diplodocus", "Supersaurus", and "Amphicoelias", and the ornithischians "Camptosaurus", "Dryosaurus", and "Stegosaurus". "Allosaurus" is commonly found at the same sites as "Apatosaurus", "Camarasaurus", "Diplodocus", and "Stegosaurus". The Late Jurassic formations of Portugal where "Allosaurus" is present are interpreted as having been similar to the Morrison but with a stronger marine influence.
Apatosaurus was found a short distance from a skeleton (specimen CM3018) identified as the new species "Apatosaurus louisae", named after Louise Carnegie, wife of Andrew Carnegie, who funded field research to find complete dinosaur skeletons in the American West. The skull was designated CM11162; it was very similar to the skull of "Diplodocus". Another smaller skeleton of "A.louisae" was found nearby CM11162 and CM3018. The skull was accepted as belonging to the "Apatosaurus" specimen by Douglass and Carnegie Museum director William H. Holland, although other scientistsmost notably Osbornrejected this identification. Holland defended his view in 1914 in an address to the