Due to all of the adults being killed in the bombings carried out nearly a decade ago, all Brachiosaurs on Nublar are decedents of juveniles that had sought shelter during the fires; or unhatched eggs in the laboratories.
- Male: Mainly a pale green and gray mottling, with pale yellow striping on their bodies and a red crest.
- Female and juvenile (both sexes): Brown and gray mottling, with some individuals having darker striping.
Brachiosaurus can be found in wide-open spaces where there is sufficient tree coverage, often close to a water-source such as a lake or a river, where they may bathe.
Brachiosaurus females live in small groups of 5-10 individuals dominated by a single matriarch. These herds are well-spread out so that they do not overgraze. Long-distance communication and mating contests are carried out through song-like calls. Males are more solitary, seeking out the female groups when it is time to breed.
Brachiosaurus is by far the largest dinosaur on Isla Sorna, indeed the biggest animal cloned by InGen. Yet despite its enormous weight and volume, Brachiosaurus is surprisingly graceful when in motion. Its long neck allows the animal to reach heights of up to 14-15 metres (even higher when the dinosaur rises up on its hind legs), enabling it to feed on treetop foliage inaccessible to all other herbivorous dinosaurs. As well as its huge size and long neck, this sauropod is also easily recognizeable for its considerably longer forelimbs than its hindlimbs, resulting in its distinctive downward-sloping back, as well as its relatively short tail. The Brachiosaur’s head is tiny and high-crested, with nostrils on the forehead, and teeth shaped like chisels.
Brachiosaurus is a peaceful animal that enjoys the company of various different species of herbivorous dinosaur such as hadrosaurs and other sauropods, and can often seen grazing together in harmony. Brachiosaurus keep in constant contact with one another over long distance through a variety of musical honks and bugles as well as infrasonic booms which can travel incredible distances. Their song-like calls are also used to settle disputes between individuals, and to warn others of approaching danger.
Fights between Brachiosaurus are practically non-existent, with disputes normally being settled by their calls and in extreme circumstances, by standing side by side and shoving one another until one backs down. It is its massive size which makes the sauropod so dangerous; in that when agitated, Brachiosaurus pays little attention to where it steps. Full-grown Brachiosaurus typically have little to fear from carnivores Ceratosaurus-sized or smaller. Even Tyrannosaurus tend to avoid them; with the pack hunting Giganotosaurus being the biggest threat.
After mating, female Brachiosaurus will congregate together, often amongst Apatosaurus and Mamenchisaurus, to lay their eggs in mass nests in dirt or sand. The adults then quickly move away due to the risk of crushing the eggs and hatchlings with their large feet. Some individuals may remain at a distance in order to discourage predators; however the football-sized eggs are greatly sought after and a majority of the eggs and hatchlings are taken by small nest raiders such as Gallimimus, Segisaurus, Ornitholestes, and Herrerasaurus, thus helping to keep the numbers of these gigantic dinosaurs under control. The hatchlings that survive remain hidden amongst the forests and when grown large enough, the young Brachiosaurus join the feeding groups of adults. Although still vulnerable to canivores, the young benefit from the protection the larger individuals provide.