Name: Brachiosaurus (Arm lizard). Phonetic: Brak-he-o-dore-us. Named By: Elmer S. Riggs - 1903. Classification: Chordata, Reptilia, Dinosauria, Saurischia, Sauropoda, Titanosauriformes, Brachiosauridae. Species: B. altithorax (type). Type: Herbivore. Size: Approximately 26 meters long. Known locations: USA, Morrison formation. Time period: Kimmeridgian of the Jurassic. Fossil representation: Several specimens, the most complete of which is believed to have come from a sub adult.
Brachiosaurus earned its name from the fact that the arms, or rather the fore legs as it was quadrupedal, are actually longer than the hind legs. The fact that these are longer offers Brachiosaurus a passive advantage in reaching up into the tree canopy to feed as the neck is always arched upwards as a result. Since the skeleton and vertebrae would be angled in such a way, Brachiosaurus would not need extra powerful muscles to lift the head and neck all the way up, reducing the effort to feed in such a specialised way. A further adaptation were the presence of air sacs located along the neck and trunk of Brachiosaurus. These connected to the lungs and had the effect of lowering the body density which in turn would reduce the total weight of the neck and trunk areas. These adaptations meant that Brachiosaurus could easily live the life of a high browser feeding upon the tree canopy. Such specialisation also meant that Brachiosaurus would not have to compete with other herbivorous dinosaurs such as the low browsing Stegosaurus. Brachiosaurus could not chew its food as its jaws were only capable of opening and closing. Because of this it would use its spatulate (chisel like) teeth to crop the vegetation from the tops of trees. Its possible that Brachiosaurus was gigantothermic meaning its massive body would hold onto body heat for longer than a smaller animal. This would give Brachiosaurus a higher metabolism than a 'standard' cold blooded or 'ectothermic' animal. However, the air sacs that would have been present inside of the body may also have provided extra cooling allowing Brachiosaurus to lower its body temperature and metabolism. This would also reduce the required calorie intake to keep its body going, reducing the required amount of time for feeding.