Brachiosaurus

Brachiosaurus is the type genus of Brachiosauridae. Riggs coined the name "arm lizard" in 1903 because the forelimbs are unusually long. Most sauropods have shorter forelimbs than hindlimbs; Brachiosaurus does the opposite. The result is a strongly inclined back and a giraffe-like, high-browsing silhouette.

The Morrison material Riggs described is the only universally accepted Brachiosaurus material. The famous Tendaguru material from Tanzania, described by Werner Janensch in 1914 as Brachiosaurus brancai, was reassigned to its own genus Giraffatitan by Mike Taylor in 2009. Most subsequent workers have followed Taylor on the split. B. altithorax itself is a sub-adult: the holotype (FMNH P 25107) is a partial postcranium with no skull. Skull material referred to Brachiosaurus sensu lato gives the classic high-arched cranium with spoon-shaped teeth.

Mass estimates have swung wildly. Early 20th-century estimates pushed past 80 tonnes. Modern volumetric reconstructions place the holotype at 28–35 tonnes for a sub-adult, with adults possibly reaching 50.

Brachiosaurus shared the Morrison Formation with Diplodocus, Apatosaurus, Camarasaurus, Stegosaurus, and Allosaurus. As a high-browser, it filled a niche the low-slung diplodocids couldn't reach: conifer canopies. The trickier question is the cardiovascular one. Pumping blood to a head 9 m off the ground is a serious problem. Solutions in the literature include an unusually large heart, accessory neck pumps, or simply a habitually lower neck angle than the most extreme reconstructions show. None of those is fully settled.

• Brachiosaurus altithorax holotype (FMNH P 25107) — Field Museum of Natural History; partial postcranium.
• Felch Quarry specimen — Yale Peabody Museum; long-debated whether it represents Brachiosaurus or close relative.
• Other Morrison material referred to Brachiosaurus — fragmentary, from Colorado, Utah, and Wyoming.

Taylor (2009) split the African material into Giraffatitan, leaving Brachiosaurus as a North American genus. The split is widely but not universally accepted. Mass estimates have settled well below early 20th-century numbers but still vary by author. Neck posture is genuinely contested: full vertical, a sub-vertical "alert posture," and a more habitually horizontal carriage have all been argued in the literature.

Brachiosaurus is the first dinosaur Grant and Ellie see in Jurassic Park (1993), calmly browsing a tree. The scene still gets cited as one of the most affecting dinosaur shots ever filmed. It also appears in the Jurassic World films, in Fantasia, and in countless children's books.

• brachiosauridae
• sauropodomorpha
• diplodocus
• apatosaurus
• camarasaurus

• Riggs, E. S. (1903). Brachiosaurus altithorax, the largest known dinosaur. American Journal of Science, 15, 299–306.
• Taylor, M. P. (2009). A re-evaluation of Brachiosaurus altithorax and its generic separation from Giraffatitan brancai. Journal of Vertebrate Paleontology, 29, 787–806.
• Paul, G. S. (1988). The brachiosaur giants of the Morrison and Tendaguru. Hunteria, 2, 1–14.
• Sander, P. M., et al. (2011). Biology of the sauropod dinosaurs. Biological Reviews, 86, 117–155.