Brachiosaurus

About Brachiosaurus

Features - Ecology and the Controversy over Neck Posture

The most prominent feature of Brachiosaurus is that its forelimbs are longer than its hindlimbs, and its spine slopes backward from the shoulders to the hips. Due to this unique proportion, it could keep its head at an extremely high position (9.4 meters to a maximum of 13 meters). Its estimated weight reached 28.3 to 46.9 tons.

They had a different dietary style from other sauropods. They selectively ate the leaves of tall trees such as conifers, ginkgos, and large cycads at a height of 5 to over 9 meters above the ground. Because leaves at high altitudes do not have sand or mud attached, their teeth did not wear out easily, and the time it took for their teeth to be replaced was about 83 days, which was very slow compared to other sauropods (Diplodocus was about 35 days). They spent up to 16 hours a day eating, tearing off large amounts of leaves with chisel- or spoon-shaped teeth, swallowing them whole without chewing, and fermenting them in their huge intestines for digestion.

In the past, it was thought that "Brachiosaurus was a cold-blooded animal (ectotherm)" to maintain such a huge body. This is because if they were warm-blooded (endotherms), it was expected that they would not be able to release the heat generated inside their bodies, overheat and die.
However, as a result of analyzing fossilized teeth with the latest technology (clumped isotope thermometer) in 2011, it was proved that their body temperature in life was about 38.2 degrees Celsius, and they were active warm-blooded animals just like mammals. To prevent overheating due to their massive bodies, it is thought that they had a powerful cooling system that efficiently released body heat to the outside using a huge nasal arch on top of their heads and a system of air sacs spread extensively inside their bones.

For many years, it was thought that the towering long neck was held vertically high like a giraffe, and it has been depicted that way in many restorations. However, recent biomechanical studies have reconsidered this image.

To pump blood to a brain high off the ground would require a blood pressure twice that of a modern giraffe and a massive heart, which is physiologically unrealistic. Current research concludes that the most stable posture with the least strain on the bones and intervertebral discs was not to hold the neck completely vertical, but to keep it at a diagonal upward angle of about 60 to 70 degrees from the ground.

Habitat of Brachiosaurus

It was once thought that "Brachiosaurus lived in water such as swamps." It was believed that they used buoyancy in the water to support their large weight, like modern hippopotamuses, and breathed with only the nostrils on top of their heads sticking out of the water surface.

However, this "aquatic life theory" is now completely rejected. If a creature as huge as a Brachiosaurus dove deep into the water, tremendous water pressure would be applied to its chest. Since dinosaurs did not have a diaphragm like humans, their lungs would be crushed by the water pressure and they would be unable to breathe.
Furthermore, according to recent biomechanical studies calculating the forces acting on the cartilage of their limb joints, vigorous exercise or running was impossible, and it was found that they walked slowly near the endurance limit of their joints. Rearing up on their hind legs alone was also physically impossible. For these reasons, the view that they lived completely on land has become the established theory.

By the way, an interesting theory has been proposed in recent years about why the nostrils were on top of the head. With a long neck and long forelimbs, it was difficult for Brachiosaurus to lower its head to the ground to drink water. Therefore, when drinking water in a river or lake, it is thought that they may have stretched their necks straight down, submerged their snouts deep into the water, and drank water while continuing to breathe by keeping only the nostrils on top of their heads above the water surface.

Discovery and Classification - Relationship with Giraffatitan

In 1900, American paleontologist Elmer Riggs discovered a huge bone in an abandoned goat ranch in Colorado. Initially, due to its immense size, he mistook it for a poorly preserved Apatosaurus femur and tried to put it off, but later discovered a real, even larger femur, and realized that the bone he found earlier was a humerus (forelimb bone). Due to the unprecedented feature of the forelimbs being longer, he was convinced that he had discovered the largest dinosaur in history.

Judging from the situation at the excavation site, it is thought that the front half of this individual was washed away by the strong current of a river after death, and only the back half, which was deeply buried in mud, miraculously remained as a fossil. In 1903, Riggs officially published a paper naming it "Brachiosaurus altithorax", meaning "arm lizard with a deep chest".

Between 1909 and 1912, many well-preserved complete sauropod skeletons were excavated in Tanzania, East Africa. Because these were similar to the North American Brachiosaurus, they were named as a new species, "Brachiosaurus brancai". For many years, this complete African skeleton has been exhibited in museums around the world as the "representative of Brachiosaurus" and has been a model for encyclopedias.

However, in 2009, paleontologist Michael Taylor compared the skeletons of both in detail and proved that there were too many differences in bone shape (26 places) to classify them in the same genus. The original North American Brachiosaurus had a longer torso, a deeper rib cage, and a longer, sturdier tail than the African one.
As a result, the African species was separated and reclassified as a different genus, "Giraffatitan". Currently, the genus Brachiosaurus in a strict sense refers to only one species discovered in North America (Brachiosaurus altithorax).

New Discoveries - Excavations in Utah

Because Brachiosaurus lived only in limited environments along tall tree-rich rivers within a geological formation called the Morrison Formation, their fossils are extremely rare, with only about 10 individuals discovered to date. This contrasts with other giant sauropods (such as Camarasaurus and Diplodocus), of which hundreds of individuals have been found.

However, in 2019, a massive Brachiosaurus humerus was newly discovered in a rugged desert area of Utah. The site was an extremely desolate, remote area where vehicles and heavy machinery could not enter. So the excavation team brought in two large Clydesdale draft horses to the site and successfully pulled out the fossil, which was over 2 meters long and weighed over 450 kilograms, using horsepower, an unusual classic method that became a hot topic.

This fossil was found in the oldest strata discovered so far, making it a very important discovery indicating that Brachiosaurus appeared and settled on the North American continent from an early stage of the Late Jurassic.