Brachiosaurus

Neck Bones like a Balloon

If you try to make a model of a Brachiosaurus with its neck extended forward, the long, heavy neck would make it lose balance and topple over. An actual Brachiosaurus didn’t have this problem because its neck was light, and its body was heavy at the back. A CT scan of a Brachiosaurus’s neck bones reveals that the inside was almost completely hollow. This made its neck light, while its leg and tail bones were solid, keeping its center of gravity toward the back. It’s believed that the neck bones of juveniles were solid but became hollowed out as they grew. As an adult, the interior of the neck bones was almost entirely hollow, with the surface and internal structures being very thin—the thinnest parts were even thinner than a postcard.

An adult Brachiosaurus’s neck bones were like balloons made of thin bone. With such thin bones, it couldn’t support large muscles. Therefore, it’s thought that its neck had almost no muscle. In older reconstructions, it’s depicted with a thick, muscular neck, but in reality, such muscles would have broken the thin bones.

So how did it support its neck? It must have had ligaments connecting the bones, so it is likely that the ligaments alone supported the bones from its back to its neck.

It supported its bones from its back to its neck with ligaments alone.

The bodies of super-sized sauropods like Brachiosaurus are thought to have had a “suspension bridge” structure. A suspension bridge hangs its deck from towers with wires extending from the towers to both ends of the bridge. Similarly, with Brachiosaurus, its hind legs and pelvis served as the towers, and the ligaments (acting as wires) suspended the bones of its neck in the front and tail in the back.

With almost no muscles in its neck and the bones being supported only by ligaments, its neck was likely very stiff, like a balloon hanging by a string, and could not be moved much.

Why the Long Neck?

To sacrifice function in favor of making bones light and muscles minimal—all to make the body bigger and emphasize the length of the neck. It seems it evolved this way to be big and have a long neck without being too heavy. The question is, why was it so necessary to have such a large body and a long neck?

It was once thought that its neck grew long to reach the leaves of tall trees. However, with almost no muscles and a structure that couldn’t bend upward, it would have been impossible for it to lift its head up. The limit was likely keeping its head nearly horizontal at shoulder height. Since its shoulder was about 5 meters off the ground, it could reach trees as tall as a giraffe without needing to raise its neck. Also, if it had held its head high, it would have required a heart of an impossibly huge size to pump blood to its head. Raising its neck high was impossible in every way.

On the other hand, it needed to lower its neck to drink water, so it had some muscles to do so. It likely lowered its neck by contracting the muscles on the underside of its neck and then let it rise back to its natural position by relaxing them.

A Brachiosaurus drinking water

There seems to be no logical reason for its long neck. In fact, a long neck was likely a handicap. With a 9-meter neck, a single breath would take tens of seconds. It could only take a few breaths per minute, so it naturally couldn’t engage in strenuous activity. Furthermore, it would have taken a considerable amount of time for food to reach its stomach.

So, why did it have such a long neck? A hint is that juveniles didn’t have very long necks.

A feature that is absent in juveniles and only develops as an adult is likely for sexual display. It was a feature to show off to potential mates and rivals. In the world of Brachiosaurus, it’s thought that the longer the neck, the more attractive it was to mates. This is why it is believed to have evolved a long neck, even though it had few benefits and many drawbacks in its daily life.

Brachiosaurus Skeleton

Its arms were long, and its shoulders were positioned higher than its hips, much like a giraffe.

It was once thought to be a semi-aquatic animal, but the slimness of its limbs and other evidence have led to the conclusion that it was entirely a land-dwelling animal.

It was also believed that its nostrils were on the top of its head, acting like a snorkel, but recent theories suggest that they were likely located near the tip of its snout.

The Diet of Sauropods

Sauropods, including Brachiosaurus, were huge, and their food—plants—had low nutritional value and was difficult to digest. Therefore, they had to eat a lot. They likely ate almost non-stop throughout the day, hardly sleeping.

A Brachiosaurus eating

A wild elephant spends about 20 hours a day eating. It needs to eat that much to maintain its huge body.

Sauropods were much larger than elephants, but a day only has 24 hours, so they couldn’t possibly spend more time eating than an elephant. It’s likely that sauropods spent about 20 hours a day eating, similar to an elephant. Sauropods had a higher metabolic efficiency due to a process called “inertial homeothermy,” which allowed them to maintain their huge bodies with a similar amount of food as an elephant.

The Great Migration of Sauropods

The discovery of numerous dense sauropod footprints suggests that they traveled in very large herds. A herd of hundreds of such massive creatures on the move would have been a sight to behold. These herds likely created paths wherever they went, not just along rivers and coasts, but possibly even through forests.

A herd of Brachiosaurus on the move

Since their lives were almost entirely about eating, they likely lived by slowly wandering and grazing in areas with abundant plants. They didn’t move aimlessly; their routes were probably fixed. They would eat the plants along their path.

By the time they completed a cycle and returned to their starting point, the plants would have grown back, creating a sustainable cycle that allowed them to thrive for over 100 million years without a shortage of food.