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 is said to have reached 28.3 tons to 46.9 tons.

It had a different feeding style from other sauropods. It selectively ate the leaves of tall trees such as conifers and ginkgoes at heights of 5 to over 9 meters above the ground. Because the leaves at high places were free of sand and mud, its teeth did not wear out easily, and the time it took to replace its teeth 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, biting off large amounts of leaves with chisel or spoon-shaped teeth, swallowing them whole without chewing, and fermenting them for digestion in their huge intestines.

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

Pumping 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 burden on the bones and intervertebral discs was not to make the neck completely vertical, but to hold it at a diagonal upward angle of about 60 to 70 degrees from the ground.

Where Brachiosaurus Lived

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

However, this "aquatic life theory" has now been completely denied. If a creature as huge as a Brachiosaurus dove deep into the water, tremendous water pressure would be applied to its chest. Because dinosaurs did not have a diaphragm like humans, their lungs would be crushed by the water pressure and they would not be able to breathe.
In addition, according to recent biomechanical studies that calculated the forces acting on the cartilage of the joints of their limbs, strenuous exercise and running were impossible, and it has been found that they walked slowly near the durability limit of their joints. Standing 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.

Incidentally, an interesting theory has been proposed in recent years regarding the reason why the nostrils were on the 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 in the water, and drank water while continuing to breathe by sticking only the nostrils on the top of their heads above the water surface.

Discovery and Classification: Relationship with Giraffatitan

In 1900, American paleontologist Elmer Riggs discovered a huge bone on 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, realizing that the bone he found earlier was a humerus (forelimb bone). Because of the unprecedented characteristic that the forelimbs were 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 the body of this individual was washed away by the strong current of a river after death, and only the rear 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, a large number of well-preserved full skeletons of sauropods were excavated in Tanzania, East Africa. Since these were similar to the Brachiosaurus of North America, 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 a "representative of Brachiosaurus" and has been a model for encyclopedias.

However, in 2009, paleontologist Michael Taylor compared the skeletons of the two in detail and proved that there were too many differences in bone shape (26 places) to put them in the same genus. The original North American Brachiosaurus had a longer torso, 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 rivers rich in tall trees within a geological formation called the Morrison Formation, their fossils are extremely rare, and only about 10 individuals have been discovered to date. This is in contrast to other giant sauropods (such as Camarasaurus and Diplodocus), of which hundreds of individuals have been found.

However, in 2019, a huge humerus of Brachiosaurus 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 draft horses of the Clydesdale breed and successfully pulled out the fossil, which was over 2 meters long and weighed more than 450 kilograms, using horsepower, an unusual classical method that became a hot topic.

This fossil was found in the oldest stratum 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.