| Named By: | Othniel Charles Marsh in 1877 |
| Time Period: | Late Jurassic, 150 Ma |
| Location: | USA, Colorado - Morrison Formation |
| Size: | Unknown |
| Diet: | Herbivore |
| Fossil(s): | Two vertebrae |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Sauropoda | Diplodocoidea | Apatosaurinae | |
| Also known as: | | Titanosaurus montanus | |
Atlantosaurus (meaning "Atlas lizard") is a dubious genus of sauropod dinosaur. It contains a single species, Atlantosaurus montanus, from the upper Morrison Formation of Colorado, United States. Atlantosaurus was the first sauropod to be described during the infamous 19th century Bone Wars, during which scientific methodology suffered in favor of pursuit of academic acclaim.