Apatosaurus, the correct name for what is also known as Brontosaurus, was approximately 20 feet shorter and 32 tons lighter than Brachiosaurus. Apatosaurus stood 30 to 35 feet tall and 65 to 75 feet long, weighing 18 tons. It had a 15- to 17-foot neck. The Brachiosaurus was 40 to 50 feet high and 85 to 95 feet long, weighing more than 50 tons. It had a 30-foot neck.
Both Apatosaurus and Brachiosaurus were members of the sauropod family and were among the largest land animals ever. Both lived during the Jurassic Period, 146 to 157 million years ago.
The name Brachiosaurus means “arm lizard,” due to its limbs being unusually long for a sauropod.
The name Apatosaurus means “deceptive lizard," because when an incomplete set of fossils was discovered in 1877, it was originally confused with Mosasaurus. Later, in 1879, paleontologist Othniel C. Marsh named one of his fossil set discoveries Brontosaurus excelsus, which means "thunder lizard." In 1903, scientists at the Carnegie Museum realized that the bones used to reconstruct the Brontosaurus were actually a combination of remains from the species Apatosaurus, mixed with the head of a Camarasaurus. Although the name Apatosaurus came first, the name Brontosaurus has become better known.