Brachiosaurus and Camarasaurus: similarities and differences

Brachiosaurus and Camarasaurus lived in the Late Jurassic of North America and were large herbivorous sauropods. Popular reconstructions can make them look alike because both had long necks and heavy bodies. Their limb proportions, skull shapes and likely feeding heights, however, were noticeably different.

“Brachiosaurs” can refer to the family Brachiosauridae, whereas Brachiosaurus is one particular genus. Camarasaurus belongs to another branch of Macronaria and is not a species of Brachiosaurus.

At a glance

Body proportions

The name Brachiosaurus means “arm lizard”. Its upper arm bone was very long, and its forelimbs exceeded its hind limbs in length. The shoulder girdle sat high, the trunk sloped down toward the pelvis, and the neck rose markedly from the front of the body.

Camarasaurus also had powerful forelimbs, but they did not create the same high-shouldered outline. Its body appeared more compact. The neck was built from large, pneumatic vertebrae, and its tail was shorter and more robust than that of Diplodocus.

Skull and teeth

The skull of Camarasaurus is much better known than those of many sauropods. It was short and deep, with large openings that kept the bones relatively light. The genus name refers to chambers in its vertebrae, not to openings in the skull.

The skull of a brachiosaurid was more elongated. The bony nostrils sit high on the skull, but the fleshy nostrils of the living animal need not have been at the very top of the head. Older pictures that placed them almost between the eyes read the fossil openings too literally.

Both genera had large, spoon-shaped teeth that could strip relatively tough vegetation. Their teeth were replaced through life. They did not have the grinding surfaces of mammalian molars.

How high did they feed?

The high shoulders and long neck gave Brachiosaurus a greater vertical reach. It could use vegetation beyond the reach of lower-bodied sauropods. That does not mean its head was always held at maximum height: the animal could change posture while moving and feeding.

Camarasaurus probably fed more often at middle heights. Its strong teeth and broad skull differed from the narrow muzzle of diplodocids. Several sauropod species in one ecosystem may have divided food resources by plant type and feeding height, although overlap was also possible.

Size

The type species, Brachiosaurus altithorax, is known from a partial skeleton in the Morrison Formation. Its length is usually reconstructed at roughly twenty metres, and mass estimates reach several tens of tonnes. The African giraffatitan was long classified as a species of Brachiosaurus, but most researchers now recognise it as a separate genus. Many famous museum outlines labelled “Brachiosaurus” are in fact based on Giraffatitan.

Camarasaurus commonly reached about 15–18 m, with size varying by species and age. It was shorter than large brachiosaurids but had a heavy trunk. Direct comparison of mass is less certain because the Brachiosaurus skeleton is incomplete.

Air spaces in the skeleton

The vertebrae of both animals contained complex spaces associated with air sacs. Pneumaticity reduced the mass of the neck and trunk while leaving strong internal struts. In Brachiosaurus, air-filled extensions also entered some ribs.

This anatomy shares a broad principle with the respiratory system of birds. It does not mean that sauropod bones were empty tubes: walls and internal braces distributed the loads. Fossils preserve the cavities and struts; the complete soft-tissue arrangement is inferred.

Where and when they lived

Both genera are known from the Morrison Formation in western North America, which dates to the Late Jurassic. Camarasaurus is represented by many skeletons of different ages and is one of the formation's most common sauropods. Brachiosaurus is much rarer.

Diplodocus, Apatosaurus, Stegosaurus, Allosaurus and many other dinosaurs shared the broader fauna. Their fossils in the same formation do not mean that every species lived in the same herd or occupied the same patch of habitat at one time.

How reconstructions changed

During the twentieth century, Brachiosaurus was often shown as a semi-aquatic animal that supposedly used its high head to breathe underwater. Water pressure would have made such breathing difficult, and sauropod limbs and trackways instead support a terrestrial way of life.

Camarasaurus was sometimes given an excessively heavy, cumbersome posture. Modern skeletal reconstructions place its limbs beneath its trunk and do not drag the tail along the ground. New research has not made these animals less massive; it has returned them to a more biologically plausible range of movement.

Relationship

Both genera belong to Macronaria, a major branch of the sauropod family tree described in the dinosaur encyclopedia. Camarasaurus lies closer to the base of this branch. Brachiosaurids are titanosauriforms, within the lineage that also leads toward titanosaurs.

Their similarities are not accidental, but Brachiosaurus did not descend from Camarasaurus. They were different branches that lived at the same time, sharing a general body plan while evolving different specialisations.