Apatosaurus

Apatosaurus, a diplodocid sauropod from the Late Jurassic, is among the most recognisable Mesozoic herbivores. Othniel Charles Marsh named the type species, A. ajax, in 1877 using material found at Como Bluff, Wyoming. Two years later, he described Brontosaurus excelsus from similar remains. Elmer Riggs re-evaluated these in 1903, concluding that Brontosaurus was a junior synonym of Apatosaurus. This remained the consensus for over a century until 2015, when a specimen-level analysis by Tschopp, Mateus, and Benson suggested that Brontosaurus should be resurrected as a distinct genus. While many paleontologists have adopted this change, the split remains a point of contention in the field.

The animal followed a classic diplodocid body plan but was built more robustly than its relative Diplodocus. Its neck was long, though slightly shorter than that of Diplodocus, and featured sturdy vertebrae with bifid neural spines and complex pneumatic structures. Its limbs were columnar and its tail was long and whip-like. Early reconstructions of Apatosaurus used Camarasaurus skulls, leading to decades of scientific error regarding its appearance. The correct skull type was not definitively associated with the genus until 1979.

Apatosaurus shared its Morrison Formation habitat with other giants like Diplodocus, Brachiosaurus, and Camarasaurus, as well as predators like Allosaurus. Fossil trackways indicate that these sauropods likely moved in herds. Biomechanical studies of skull and tooth wear suggest they were low-to-mid-level browsers. Like its relatives, Apatosaurus possessed a whip-like tail that may have served as a defensive or display tool. Models developed by Conti et al. (2022) suggest that the tail tip could have produced supersonic cracks like a bullwhip, potentially creating an incredibly loud noise.

According to bone histology, Apatosaurus reached its adult size in about 8 to 12 years. These dinosaurs likely lived between 30 and 80 years, remaining reproductively active throughout most of their adult lives.

• Apatosaurus louisae holotype (CM 3018) — Carnegie Museum; one of the most-mounted sauropod skeletons in the world.
• CM 11162 — second key Carnegie specimen.
• YPM 1860 — original Marsh material.
• Brontosaurus excelsus (resurrected) holotype (YPM 1980) — Yale Peabody Museum.

Brontosaurus split — Tschopp et al. (2015) resurrected Brontosaurus as separate; some workers accept, some don't. Whip-tail supersonic crack — biomechanically defensible. Species count — A. ajax, A. louisae, A. parvus (or Brontosaurus parvus), A. yahnahpin (or Eobrontosaurus) — under various splittings.

Apatosaurus / Brontosaurus is the platonic "long-neck" of The Land Before Time (Littlefoot is generically diplodocid), the Sinclair Oil dinosaur, and countless children's books. The 2015 Brontosaurus resurrection generated international news coverage and a brief consumer-confusion media moment.

• diplodocidae
• diplodocus
• brachiosaurus
• camarasaurus
• allosaurus

• Tschopp, E., Mateus, O., & Benson, R. B. J. (2015). A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae. PeerJ, 3, e857.
• McIntosh, J. S. (1981). Annotated catalogue of the dinosaurs (Reptilia, Archosauria) in the collections of Carnegie Museum of Natural History. Bulletin of Carnegie Museum, 18, 1–67.
• Riggs, E. S. (1903). Structure and relationships of opisthocoelian dinosaurs. Part I. Apatosaurus Marsh. Field Columbian Museum Publication, 82, 165–196.
• Conti, S., et al. (2022). Multibody analysis and soft-tissue strength refute supersonic dinosaur tail. Scientific Reports, 12, 19245.