Brachiosaurus

About Brachiosaurus

Features - Ecology and the Neck Posture Controversy

The biggest feature of Brachiosaurus is that its forelimbs were longer than its hindlimbs, and its spine sloped backward from its shoulders to its hips. Due to this unique proportion, it was able to keep its head at an extremely high position (9.4 meters to a maximum of 13 meters). Its estimated weight is said to reach 28.3 to 46.9 tons.

They had a different feeding style from other sauropods. They selectively ate the leaves of tall trees such as conifers and ginkgoes located 5 to over 9 meters above the ground. Because leaves at high altitudes do not have sand or mud on them, their teeth did not wear out easily, and the period required for tooth replacement was about 83 days, which was very slow compared to other sauropods (about 35 days for Diplodocus). They spent as much as 16 hours a day eating, biting off large amounts of leaves with chisel or spoon-shaped teeth, swallowing them whole without chewing, and fermenting and digesting them in their huge intestines.

In the past, to maintain such a huge body, it was thought that "Brachiosaurus was a cold-blooded animal (ectotherm)". This is because if it were a warm-blooded animal (homeotherm), it was predicted that it would not be able to release the heat generated inside its body and would die of overheating.
However, as a result of analyzing fossilized teeth with the latest technology in 2011, its body temperature during its life was about 38.2 degrees Celsius, proving that it was an active warm-blooded animal just like mammals. To prevent overheating due to its massive body, it is thought to have possessed a powerful cooling system to efficiently release body heat to the outside, utilizing a huge nasal arch on top of its head and air sacs spread extensively inside its bones.

For many years, it was thought that its long neck towering high in the sky was raised vertically like a giraffe, and it was drawn that way in many restorations. However, recent biomechanical research has reconsidered this image.
Sending blood to the brain located high off the ground would require twice the blood pressure of a modern giraffe and a massive heart, which is physiologically unrealistic. Current research concludes that the neck was not held completely vertical, but rather kept diagonally upward at about 60 to 70 degrees from the ground, which was the most stable posture with the least burden on the bones and intervertebral discs.

Where Brachiosaurus Lived

It used to be thought that "Brachiosaurus lived in water such as swamps". This is because to support its heavy weight, it was thought to use the buoyancy in the water like a modern hippopotamus, breathing with only the nostrils on top of its head sticking out of the water surface.

However, this "aquatic lifestyle theory" is now completely denied. If a creature as huge as a Brachiosaurus dives deep into the water, tremendous water pressure is 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 be unable to breathe.
Also, according to the latest biomechanical research calculating the forces acting on the cartilage of their limb joints, intense exercise or running was impossible, and they were walking slowly near the endurance limit of their joints. Rearing up on their hind legs was also physically impossible. For these reasons, the view that they lived entirely on land has become the established theory.

By the way, an interesting theory has been proposed recently regarding the reason why the nostrils were located on top of the head. With a long neck and long forelimbs, it was hard for Brachiosaurus to lower its head to the ground to drink water. Therefore, it is thought that when drinking water in rivers or lakes, it stretched its neck straight down, sank its snout deep into the water, and drank while continuing to breathe by leaving only the nostrils on top of its head above the water surface.

Discovery and Classification: Relationship with Giraffatitan

In 1900, American paleontologist Elmer Riggs discovered huge bones at an abandoned goat ranch in Colorado. Initially, due to their sheer size, he mistook them for "poorly preserved Apatosaurus femurs (hind leg bones)" and was going to put them off, but after discovering a genuine, even larger femur later, he realized that the bone he found first was a humerus (front leg bone). From the unprecedented feature of having longer front legs, he was convinced that he had discovered the largest dinosaur in history.

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

From 1909 to 1912, many exceptionally well-preserved complete skeletons of sauropods were excavated in Tanzania, East Africa. Because these were similar to the North American Brachiosaurus, they were named the 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 served as a model for encyclopedias.

However, in 2009, paleontologist Michael Taylor made a detailed comparison of their skeletons and proved that there were too many differences in bone shape (26 locations) to classify them in the same genus. The original North American Brachiosaurus had a longer torso, a deeper rib cage, and a longer, more robust tail than the African one.
As a result, the African species was made independent and reclassified as the separate genus "Giraffatitan." Currently, the genus Brachiosaurus in the strict sense refers only to the single species discovered in North America (Brachiosaurus altithorax).

New Discoveries - Excavation 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 sharp contrast to other giant sauropods (such as Camarasaurus and Diplodocus), of which hundreds of individuals have been discovered.

However, in 2019, a huge humerus of a Brachiosaurus was newly discovered in a rugged desert area of Utah. The site was an extremely desolate, remote area where the entry of vehicles or heavy machinery was impossible. Therefore, the excavation team brought two large working horses called Clydesdales to the site, and succeeded in the unusual, classical method of towing out the fossil, which was 2 meters long and weighed over 450 kilograms, using horsepower, which became a big topic.

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