# Apatosaurus ajax

> A massive, long-necked diplodocid from the Late Jurassic Morrison Formation of the western United States. For a century it absorbed Brontosaurus, and its museum skeletons wore the wrong skull until 1979.

- Classification: Dinosauria (clade) > Saurischia (clade) > Sauropodomorpha (clade) > Sauropoda (clade) > Diplodocoidea (superfamily) > Diplodocidae (family) > Apatosaurinae (subfamily) > Apatosaurus (genus) > Apatosaurus ajax (species)
- Length: 21–23 m
- Hip height: 3.3–4 m
- Mass: 16.4–22.4 t
- Age: 154.8–143.1 million years ago (Late Jurassic)
- Fossils found in: Morrison Formation (Colorado); United States
- Diet: herbivore
- Described: Othniel Charles Marsh, 1877
- In films: Jurassic World (2015), Jurassic World: Fallen Kingdom (2018), Jurassic World Dominion (2022), Jurassic World Rebirth (2025)

Canonical page: https://dinodex.club/dinosaurs/apatosaurus-ajax
Last updated: 2026-09-27

## Overview

Apatosaurus ajax lived in western North America in the Late Jurassic. Othniel Charles Marsh named it in 1877 from a partial skeleton (YPM 1860) collected at Morrison, Colorado. In 1903 Elmer Riggs merged Brontosaurus into it, and Apatosaurus stayed the scientific name for both until 2015.

It was a very heavy sauropod with a long, deep neck and a whip-like tail. The best skeleton belongs to a second species, A. louisae (CM 3018), found at the Carnegie Quarry in Utah; a Diplodocus-like skull found nearby (CM 11162) was long rejected, and museums mounted Camarasaurus-like heads until the 1970s, when Berman and McIntosh showed the long, low skull was correct.

Bone histology suggests it grew quickly: Curry (1999) estimated that it reached near-adult size in about ten years, while later studies proposed closer to twenty.

## Name meaning

"Deceptive lizard", from Greek apatē ("deception") and sauros ("lizard"), for chevron bones Marsh thought resembled those of mosasaurs; ajax after the Greek hero (Marsh 1877).

## Sources

1. (2026). Paleobiology Database: Apatosaurus occurrences. The Paleobiology Database (paleobiodb.org), data service 1.2, accessed 2026-09-23. https://paleobiodb.org/data1.2/occs/list.txt?base_name=Apatosaurus&show=coords,paleoloc,strat,loc,ref&pgm=gplates
2. (2026). Wikipedia: Apatosaurus. Wikipedia (English), accessed 2026-09-23. https://en.wikipedia.org/wiki/Apatosaurus
3. Curry, K. A. (1999). Ontogenetic histology of Apatosaurus (Dinosauria: Sauropoda): new insights on growth rates and longevity. Journal of Vertebrate Paleontology 19: 654-665. https://doi.org/10.1080/02724634.1999.10011179
4. Holland, W. J. (1915). A new species of Apatosaurus. Annals of Carnegie Museum 10(1-2): 143-145.
5. Marsh, O. C. (1877). Notice of new dinosaurian reptiles from the Jurassic formation. American Journal of Science (series 3) 14: 514-516.
6. Paul, G. S. (2016). The Princeton Field Guide to Dinosaurs (2nd edition). Princeton University Press.
7. Tschopp, E., Mateus, O. & Benson, R. B. J. (2015). A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 3: e857. https://doi.org/10.7717/peerj.857

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Cite as: "Apatosaurus ajax". DinoDex. https://dinodex.club/dinosaurs/apatosaurus-ajax (updated 2026-09-27).