Brachiosaurus

Colossal Body and Astonishing Physical Structure

Brachiosaurus was an extra-large sauropod that was about 25 meters long and weighed a minimum of 23 tons, with some estimates reaching up to 50 tons.
This size is comparable to a modern blue whale, and it is thought that this giant grew to this size in just about 30 years.
If this giant were alive today, it could stretch its head up to look into a window on the fifth floor of a building.

Its most distinctive features were its very long neck and its forelimbs, which were much longer than its hind limbs.
Most sauropods have longer hind limbs, but Brachiosaurus had longer forelimbs, which is also the origin of its name.

A very long neck and forelimbs that are longer than the hind limbs.

The Mystery of Its Neck: The Immobile Neck and the “Suspension Bridge” Theory

In older reconstructions, Brachiosaurus was often depicted with a thick, muscular neck held vertically.
However, a computer tomography (CT) scan of a Brachiosaurus’s neck bones revealed that the inside was almost completely hollow.
It had a structure like a balloon made of thin bone, with the thinnest parts said to be thinner than a postcard.
Bones that thin could not support large muscles.

So how did it support its neck?
It is believed that the bodies of extra-large sauropods like Brachiosaurus had a “suspension bridge” structure.
With the hind limbs and pelvis as the pillars, strong ligaments, which served as the wires, suspended the bones from the neck in the front to the tail in the back.

Ligaments suspended the bones from its neck to its tail.

In this structure, the neck is thought to have been mostly immobile, making it impossible to lift its head high.
The limit was likely to keep its head in a mostly horizontal position at shoulder height (about 5m from the ground), which would still have allowed it to reach the tops of trees at a height equivalent to a giraffe.
It has also been suggested that if it had tried to force its head up, it would not have been able to send enough blood to its brain and would have fainted.

The Real Reason for Its Long Neck: A Mating Display

Why was it so necessary to make the bones light and the muscles minimal, even at the expense of function?
Why did it have to make its body so big and its neck so long?

It was once thought that it was to eat the leaves of tall trees. However, this theory has lost its credibility when considering the many handicaps of a long neck, such as taking tens of seconds for a single breath, a long time for food to reach the stomach, and an inability to perform strenuous exercise.

A hint is the fact that juveniles did not have such long necks.
A feature that is absent in juveniles but develops as an adult is often considered a sexual display for reproduction.
In the world of Brachiosaurus, it’s possible that the longer the neck, the more attractive it was to potential mates.
Despite having very few practical advantages and many disadvantages in its daily life, it is believed that Brachiosaurus evolved a long neck as a result of prioritizing reproduction over survival.

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

A Brachiosaurus drinking water

Diet, Social Behavior, and Fossil Rarity

Brachiosaurus was a herbivore with a downward-pointing snout. It is believed to have used a thick beak to pluck plants and its back teeth to grind them.
Since it was impossible for it to lift its head, which weighed nearly a ton, it couldn’t eat tall plants.
Due to its massive body and a diet of low-nutrient plants, it had to eat a lot continuously.
However, its metabolism was highly efficient due to a mechanism called “inertial homeothermy,” which allowed it to maintain its huge body with a similar amount of food as an elephant (about 20 hours a day), despite being much larger.

While Brachiosaurus was once considered a semi-aquatic animal, it is now known to have been a fully terrestrial animal.
The discovery of numerous dense footprints suggests that they traveled in large herds of hundreds of individuals.
They lived by slowly grazing in areas with abundant plants.

A herd of Brachiosaurus on the move

Instead of moving aimlessly, they maintained a rational cycle of moving along fixed routes. By the time they returned to their starting point, the plants would have grown back, allowing them to thrive for over 100 million years without a shortage of food.

Despite having such a huge body, Brachiosaurus’s skull was not very large, measuring only about 50 cm.
If an enemy appeared, it is said that it would not have fought with its small head but instead used its long tail as a weapon.

Although Brachiosaurus flourished during the Late Jurassic, fossils of this dinosaur are extremely rare and have been found almost exclusively in geological layers from that period.
However, fossils of a close relative have been discovered in Early Cretaceous layers, confirming that the brachiosaurid lineage continued to thrive long after the Jurassic period ended.

Despite its high fame, many mysteries still surround this great “arm lizard.”
New discoveries and research will undoubtedly continue to update our understanding of its appearance and life.