Apatosaurus considered a junior synonym of "Apatosaurus"; its only species was reclassified as "A.excelsus" in 1903. A 2015 study concluded that "Brontosaurus" is a valid genus of sauropod distinct from "Apatosaurus", but not all paleontologists agree with this division. As it existed in North America during the late Jurassic, "Apatosaurus" would have lived alongside dinosaurs such as "Allosaurus", "Camarasaurus", "Diplodocus", and "Stegosaurus". "Apatosaurus" was a large, long-necked, quadrupedal animal with a long, whip-like tail. Its forelimbs were slightly shorter than its hindlimbs. Most size estimates are based on specimen CM3018, the type specimen of "A.louisae". In 1936 this was measured to
Jurassic for the large herbivorous dinosaurs known as the sauropods—"Camarasaurus", "Apatosaurus", "Diplodocus", "Brachiosaurus", and many others—that roamed the land late in the period; their foraging grounds were either the prairies of ferns, palm-like cycads and bennettitales, or the higher coniferous growth, according to their adaptations. The smaller Ornithischian herbivore dinosaurs, like stegosaurs and small ornithopods were less predominant, but played important roles. They were preyed upon by large theropods, such as "Ceratosaurus", "Megalosaurus", "Torvosaurus" and "Allosaurus". All these belong to the 'lizard hipped' or saurischian branch of the dinosaurs. During the Late Jurassic, the first avialans, like "Archaeopteryx", evolved from small