Genus: Atlantosaurus MARSH, 1877 (nomen dubium)
Etymology: Greek, Atlant- (Atlas), a mythical Titan, and Greek, sauros, “lizard”: “Atlas lizard”.
= Titanosaurus MARSH, 1877 non LYDEKKER, 1877 (Titanosaurus indicus, Sauropoda, Titanosauridae)
Etymology: Greek, Titan, a mythical giant and Greek, sauros, “lizard”: “Titan lizard”.

Species: montanus (MARSH, 1877) MARSH, 1877
Etymology: In reference to the eastern flanks of the Rocky Mountains.
= Titanosaurus montanus MARSH, 1877
= Brontosaurus montanus (MARSH, 1877) KUHN, 1965

Holotype: YPM 1835

Locality: Lakes' YPM Quarry 1, T. 4S., R70W, Sec. 26, Jefferson County, Colorado.

Horizon: Member? Morrison Formation.

Biostratigraphy: Zone?

Age: Age?, Stage?, Malm Epoch, Late Jurassic.

Material: Fragmentary sacrum.