How these prehistoric animals compare
Brachiosaurus and Apatosaurus were giant plant-eating sauropods from Late Jurassic North America, but they belong to different families and had very different body proportions.
Shared Jurassic setting
Both genera are known from the Morrison Formation of the western United States, so they belong to the same geological story. Occurring in the same formation does not show that individuals met each other, because the formation covers a long span of time and a large area.
Body proportions
Brachiosaurus belongs to Brachiosauridae and had forelimbs longer than its hindlimbs, giving a sloping back and a tall shoulder. Apatosaurus belongs to Diplodocidae, with a more level back, a long neck and a long, whip-like tail. These differences are visible in the preserved bones.
Evidence and names
Apatosaurus is known from several good skeletons, while Brachiosaurus is known from less complete material, and the better-known African relative Giraffatitan was once included in the genus. Care is needed when reading older size comparisons that mix specimens of related genera.
Sources and specimen context: Brachiosaurus references · Apatosaurus references · Geological timeline
