Genus: Apatosaurus MARSH, 1877
Etymology: Greek, apatao, “deceive” and Greek, sauros, “lizard”: Deceptive lizard. Because the caudal vertebrae were first thought to belong to a mosasaur then found out it really belonged to a sauropod.

Species: ajax MARSH, 1877

Holotype: YPM 1860

Locality: Lakes' YPM Quarry 10, T4S, R70W, Sec. 35, Como Bluff, Albany County, Wyoming.

Horizon: Member? Morrison Formation.

Biostratigraphy: Zone?

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

Material: Fragmentary skeleton, with braincase and quadrates of a juvenile?
Note: Gastroliths were found? CANON, 1906.

Referred material:

= Atlantosaurus immanis MARSH, 1878

Holotype: YPM 1840

Locality: Lakes' YPM Quarry 10, T4S, R70W, Sec. 35, Como Bluff, Albany County, Wyoming.

Horizon: Member? Morrison Formation.

Biostratigraphy: Zone?

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

Material: Femur, fragmentary skeleton.
Note: Gastroliths were found? CANON, 1906.