Apatosaurus
From Greek 'apate' meaning 'deception' and 'sauros' meaning 'lizard'; meaning 'deceptive lizard'
Apatosaurus is a genus of herbivorous sauropod dinosaur that lived in North America during the Late Jurassic period. Othniel Charles Marsh described and named the first-known species, Apatosaurus ajax, in 1877, and a second species, Apatosaurus louisae, was discovered and named by William H. Holland in 1916. Apatosaurus lived about 152 to 151 million years ago (mya), during the late Kimmeridgian to early Tithonian age, and are now known from fossils in the Morrison Formation of modern-day Colorado, Oklahoma, New Mexico, Wyoming, and Utah in the United States. Apatosaurus had an average length of 21-23 m (69-75 ft), and an average mass of 16.4-22.4 t (16.1-22.0 long tons; 18.1-24.7 short tons). A few specimens indicate a maximum length of 11-30% greater than average and a mass of approximately 33 t (32 long tons; 36 short tons).
Diagnosis
- Accessory horizontal lamina in the spinodiapophyseal fossa of the mid- and posterior cervical vertebrae, not connected to any surrounding lamina
- Prezygodiapophyseal lamina of the posterior cervical and anterior dorsal vertebrae lacking a roughened lateral aspect
- Scapular blade straight in lateral view
Species (2)
Apatosaurus ajax Marsh, 1877
Type species
Named after Ajax, a hero from Greek mythology.
- Holotype
- YPM 1860 , Yale Peabody Museum of Natural History
- Material
- Nearly complete skeleton in excellent preservation.
- Horizon
- upper Brushy Basin Member, Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
- Locality
- Lakes' Quarry 10, Morrison, Colorado, United States
Apatosaurus louisae Holland, 1915
Named for Louise Carnegie, wife of industrialist Andrew Carnegie, who funded field research to find complete dinosaur skeletons in the American West.
- Holotype
- CM 3018 , Carnegie Museum of Natural History
- Horizon
- Morrison Formation, Kimmeridgian, Late Jurassic , 154.8–149.2 million years ago
- Locality
- Carnegie Quarry, near Jensen, Utah, United States
Notable specimens
-
CM 11162
Carnegie Museum of Natural History Found 1909 by Earl Douglass complementary
First Apatosaurus skull found, recovered a short distance from skeleton CM 3018 at the Carnegie Quarry. Very similar to the skull of Diplodocus, it challenged the long-held Camarasaurus-like reconstruction and sparked a decades-long dispute over the genus's true skull.
References
- Marsh, O. C. (1877). Notice of new dinosaurian reptiles from the Jurassic formation. American Journal of Science s3-14(84): 514-516. American Journal of Science (AJS). doi:10.2475/ajs.s3-14.84.514 marsh1877c
- Holland, W. J. (1915). A new species of Apatosaurus. Annals of the Carnegie Museum 9(3-4): 381-383. holland1915a
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McIntosh, J. S.; Berman, D. S. (1975). Description of the palate and lower jaw of the sauropod dinosaur Diplodocus (Reptilia: Saurischia) with remarks on the nature of the skull of Apatosaurus. Journal of Paleontology 49(1): 187-199. Cambridge University Press (CUP).
Establishes that Apatosaurus had a Diplodocus-like skull (the jawless skull CM 11162 found with the A. louisae holotype), not the Camarasaurus-like skull historically mounted on it.
mcintosh1975a - Parsons, K. M. (1997). The wrongheaded dinosaur. Carnegie Magazine. parsons1997a
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Tschopp, E.; Mateus, O.; Benson, R. B. J. (2015). A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 3: e857. PeerJ. doi:10.7717/peerj.857
Specimen-level revision of Diplodocidae providing an emended diagnosis of Apatosaurus and restricting the genus to A. ajax and A. louisae, moving other species to Brontosaurus.
tschopp2015a -
Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.
Source of the hip height estimate, and the appearance features.
jones2026b