Reptilia - Dinosauria - Diplodocidae

Alternative combination: Atlantosaurus ajax

Synonyms: Apatosaurus laticollis Marsh 1879, Atlantosaurus immanis Marsh 1878, Atlantosaurus laticollis Marsh 1879

Full reference: O. C. Marsh. 1877. Notice of new dinosaurian reptiles from the Jurassic formation. American Journal of Science and Arts 14:514-516

Belongs to Apatosaurus according to P. Upchurch et al. 2004

Sister taxa: Apatosaurus excelsus, Apatosaurus louisae

Type specimens:

• Apatosaurus ajax: YPM 1860, a partial skeleton. Its type locality is Lakes Quarry 10, Morrison (YPM), which is in a Kimmeridgian/Tithonian channel mudstone/sandstone in the Morrison Formation of Colorado.
• Apatosaurus laticollis: YPM 1861. Its type locality is Lakes Quarry 10, Morrison (YPM), which is in a Kimmeridgian/Tithonian channel mudstone/sandstone in the Morrison Formation of Colorado.
• Atlantosaurus immanis: YPM 1840. Its type locality is Lakes Quarry 10, Morrison (YPM), which is in a Kimmeridgian/Tithonian channel mudstone/sandstone in the Morrison Formation of Colorado.

Average measurements (in mm): femur length 2137.8, tibia length 1130.0

Estimated body mass: 42.1 tons based on femur length