Brachiosaurus walked on four legs and, like the other Brachiosaurids and unlike most dinosaurs, its front legs were longer than its hind legs. These unusual front legs together with its very long neck gave Brachiosaurus a giraffe-like stance and great height, up to 40-50 feet (12-16 m) tall.
Brachiosaurus was about 85 feet (26 m) long, and weighed about 33-88 tons (30-80 tonnes). It had a claw on the first toe of each front foot and claws on the first three toes of each rear foot (each foot had five toes with fleshy pads).
Like other Brachiosaurids, it had chisel-like teeth, its nostrils were on the top of its head, and it had large nasal openings indicating that it may have had a good sense of smell. Brachiosaurus had 26 teeth on its top jaw and 26 on the bottom for a total of 52 teeth towards the front of the mouth.
Brachiosaurus was an herbivore, a plant eater. It probably ate the tops of tall trees with its large spatulate (chisel-shaped) teeth. It swallowed its food whole, without chewing it, digesting the plant material in its gut.
Brachiosaurus lived in the middle to late Jurassic period, about 156-145 million years ago, near the middle of the Mesozoic Era, the Age of Reptiles. Some dating estimates have Brachiosaurus surviving until 140 million years ago, during the dawn of the Cretaceous period.
Brachiosaurus was a terrestrial animal. It was assumed for many years that giant sauropods spent most of their time in water, letting the water support their weighty bodies while breathing through their lofty nostrils. Now it is believed that they were fully terrestrial, just as Elmer S. Riggs, who first described Brachiosaurus, argued in a 1904 article. He believed, as most modern scientists do, that Brachiosaurus' feet and limbs were not broad enough to support the heavy animal in mud, that its back was flexible enough to support it on land, and that its chest was narrow and deep, which is insufficient for breathing underwater, and inconsistent with modern-day water-dwelling large animals (like hippos). A healthy, adult Brachiosaurus probably had no predators. The largest-known meat-eaters from that time (the late Jurassic period) and place (North America and Africa) were Allosaurus, Ceratosaurus, and Torvosaurus. These theropods were less than half the size of Brachiosaurus, and probably had much easier prey to hunt (like smaller sauropods and ornithischians like stegosaurs).
Brachiosaurus probably travelled in herds and may have migrated when they depleted their local food supply.
Brachiosaurus may have hatched from eggs, like other sauropods. Sauropod eggs have been found in a linear pattern and not in nests; presumably the eggs were laid as the animal was walking. It is thought that sauropods did not take care of their eggs.
Sauropod life spans may have been in the order of 100 years.
Brachiosaurus' best defense was size. In addition, its long tail could whip away most attackers. Also, they had leathery skin, although this wasn't much of a defense against long, sharp theropod teeth. They also had clawed feet that were more pronounced in the young.Brachiosaurus was first found in the Grand River Valley, in western Colorado, USA, in 1900. This incomplete skeleton was described by paleontologist Elmer S. Riggs, who named Brachiosaurus in 1903. In 1909, Werner Janensch found many Brachiosaurus fossils in Tanzania, Africa. Many Brachiosaurus fossils have been found, in North America and Africa.