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Name means: Deceptive Reptile


Species: ajax, louisae

Range: Late Jurassic (Tithonian, 150-145 MYA) from Arizona to South Dakota, including Utah, Wyoming, and Oklahoma

Size estimate: 70-75 ft length, 18-25 tons

Discovery: Othniel Charles Marsh, 1877

Classification: dinosauria, saurischia, sauropoda, diplodocidae, apatosaurinae


What makes Apatosaurus so deceptive? When scientists first found its backbones, they labeled them Mosasaur backbones. At the time, no one had ever seen a dinosaur that grew so large. Apatosaurus has tricked scientists more times than that, though. In 1903 Elmer Riggs argued that Apatosaurus and its close relative, Brontosaurus, were the same animal. 112 years later an even more detailed study found that Brontosaurus might be a distinct dinosaur after all. Scientists still have to test that idea with different methods before anyone can be sure.


Apatosaurus had a heavier build than its cousin Diplodocus. Its neck was especially thick and had a triangular cross-section. If sheer size didn’t protect them, their whip-like tails could fend off attacks. Their long necks and tails balanced evenly at their hips. This let them rear up on their hind legs for short periods. Adults could not walk on two legs, but fossil trackways show babies could run for short distances on just their hind legs.

Other dinosaurs in the world of Apatosaurus include Camptosaurus, Dryosaurus, Stegosaurus, and the sauropods Diplodocus and Camarasaurus. Although small predators like Marshosaurus, Stokesosaurus, and Ornitholestes probably didn’t pose a threat to Apatosaurus, teeth marks on some Apatosaurus bones show that Torvosaurus, Allosaurus, and Ceratosaurus may have hunted it.

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