Brachiosaurusaltithorax

Overview. In 1993, moviegoers were treated to the quintessential dinosaur blockbuster, Jurassic Park, and the animal that welcomed both the movie's characters and audiences to the park was the majestic Brachiosaurus. Towering above all other animals in the Late Jurassic Morrison Formation of western North America, Brachiosaurus was probably a high browser that had the treetops all to itself, and with an adult weight of up to 51 tons or more, it would have been virtually immune to predators. Discovered by Elmer Riggs at the start of the 20th Century, Brachiosaurus has gone on to become one of the most beloved and iconic Jurassic dinosaurs.

Discovery. Brachiosaurus was discovered in 1900 near Fruita, Colorado by Elmer Riggs, and named by Riggs in 1903. Its genus name is Greek, meaning “Arm Lizard”, and its species name means “Deep Chest”. These names reference the long arms and deep and elevated chest of Brachiosaurus which set it apart from other sauropods at the time of its discovery. The holotype (FMNH P 25107) was discovered in the Kimmeridgian aged rocks of the Brushy Basin Member of the Morrison Formation. It consisted of several ribs, the right humerus (upper arm bone), originally thought to be a femur (thigh bone), the real right femur, the right ilium (a bone in the pelvis), the right coracoid (part of a dinosaur’s shoulder blade), the sacrum (fused hip vertebrae), the seven dorsal (back) vertebrae and two caudal (tail) vertebrae. Riggs noted that the preservation quality was poor, and initially considered it just a big, badly preserved Apatosaurus, not worth studying. Thankfully, after preparing the bones in a lab, he recognized the importance of what he had found. Not only was it unique from other sauropods known at the time, but it was also the largest sauropod known.

Since then, additional, though still incomplete, Brachiosaurus remains from some 12 individuals have been reported from Colorado, Oklahoma, Utah, and Wyoming. More Brachiosaurus remains have also been reported from the holotype locality (called Riggs Hill), but the site has suffered from vandalism and looting, making the remaining fossils virtually worthless to scientists.

Evolution and Description. Brachiosaurus was a sauropod and had many of the typical hallmarks of the Sauropoda, including large size, a long neck, massive body, and pillar-like legs. Brachiosaurus belonged to a family of sauropods called Brachiosauridae, related to the camarasaurids and titanosaurs. This family also includes Abydosaurus, Giraffatitan, and Sonorasaurus, among others. Interestingly, reconstructions of Brachiosaurus are actually based on the much more complete Giraffatitan branchai, once thought to be an African species of Brachiosaurus. Brachiosaurus had a long neck which would have been held aloft like that of a giraffe, probably at about a 60–70-degree angle above horizontal, and it would have had a slight s-curve to it. It probably had a shoulder hump where the neck connected with the body. This hump was made by enlarged vertebral spines with provided extra space for muscle attachments in order to anchor the massive muscles required to support the neck. The hump wouldn’t have looked like a Bison’s hump, but rather formed the base of the neck. The front legs were longer than the back legs giving Brachiosaurus a somewhat vertically oriented torso with its shoulders higher than its hips. This elevated torso angle is partially responsible for giving it is tall neck posture. Its chest was deep, and it had a long, though only moderate by sauropod standards, tail. The skull was tall, giving it a sort of cranial “bump” where its large nostrils sat high up on the head. Its teeth were spoon shaped and would have been shed and replaced throughout the animal’s life.

Though exact size estimates vary, Brachiosaurus was undoubtedly enormous, measuring 18-22 m (59-72 ft) in length and weighing between 28.3–58 tonnes (31.2–64 tons), likely falling on the heavier end of those estimates. It would have been perhaps the heaviest dinosaur of its day, outweighing even its relative Giraffatitan and the immensely long diplodocid Supersaurus. It was also probably the tallest, standing at least 9.4 meters (30.75 ft) tall and perhaps even as tall as 12–13 meters (39–43 ft). Much of this height was neck, which posed a gravity-related challenge for getting blood up to the head. It is thought that the heart of Brachiosaurus would have weighed around 400 kg (880 lb), a massive pump to maintain the necessary blood pressure to conquer gravity and supply the head with blood.

Like most, if not all, dinosaurs, Brachiosaurus was probably warm-blooded. Such a large endothermic animal living in a warm environment would have posed a challenge of overheating. The bigger an animal is, the better it retains heat, less of a problem in cold climates, but a potentially serious threat in hot climates. African Elephants, for instance often face the risk of overheating. Their large ears are an adaptation for dumping excess heat to help avert this risk. Brachiosaurus was several times as massive, and the Late Jurassic climate was warm and tropical, so these animals would have faced similar risks. It has been suggested that the extra-large nostrils of Brachiosaurus helped to expel excess heat. Additionally, like other sauropods and theropods, Brachiosaurus had an avian-style respiratory system complete with air sacs. This made for more efficient breathing and helped to lighten the skeleton, but also probably functioned as an air-cooling system, so whenever the animal breathed, it would effectively act as its own internal air conditioner.

Ecology. Brachiosaurus lived in the Late Jurassic in the western United States in the environment represented by the Morrison Formation. The Morrison was a large, mostly flat floodplain, which had a warm tropical and probably semi-arid climate with distinct dry and wet seasons. Much of it probably consisted of scrub and fern savannah with forests of ginkgo, conifers, ferns, tree ferns, horsetails, and cycads closer to permanent sources of water. Despite the dry seasons, the environment was evidently productive enough to support Brachiosaurus, as well as several other large sauropod genera, most prominently Apatosaurus, Barosaurus, Camarasaurus, Diplodocus, Haplocanthosaurus, and Supersaurus. Compared to some of these other sauropods, Brachiosaurus may have been a more uncommon animal. There are 12 known specimens of Brachiosaurus, compared to 98 specimens of Diplodocus, 112 of Apatosaurus, and over 179 of Camarasaurus. Smaller herbivores included the large ornithopod Camptosaurus, the medium-sized ornithopod Dryosaurus, the small ornithopod Nanosaurus, the large and iconic stegosaur, Stegosaurus, and the small early ankylosaur Gargoylosaurus. Brachiosaurus would have occupied a different niche than most of these other herbivores, avoiding competition with these smaller herbivores by focusing its feeding on the treetops while the others would have been fern-grazers and low-browsers. Camarasaurus had similar teeth to Brachiosaurus and also had a somewhat vertical neck posture similar to Brachiosaurus and may have also been a high browser as well, however, Camarasaurus was smaller and shorter and so wouldn’t be able to reach as high as Brachiosaurus. Additionally, studies on the inner ears of brachiosaurids suggest that they moved their heads laterally (side to side) much more frequently than up and down, suggesting they had a very consistent browsing height which was unlikely to overlap with other sauropods, and supporting the idea of niche partitioning between Brachiosaurus, Camarasaurus, and the other Morrison herbivores. Brachiosaurus likely would have consumed about 200 to 400 kilograms (440 to 880 lb) of plant matter every day, about 1.5 % of its total body mass, which is similar to the feeding requirements of a modern elephant. Like other sauropods, Brachiosaurus didn’t chew its food. It used its spatulate (spoon shaped) to snip vegetation which it then swallowed whole and fermented in its gargantuan gut.

Herbivores weren’t the only animals living alongside Brachiosaurus. Carnivorous theropods hunted the abundance of prey. Small carnivores like Koparion, Stokesosaurus, and Ornitholestes would have posed no threat to Brachiosaurus past the hatchling stage. Larger theropods like Allosaurus and Ceratosaurus may have been threats to juvenile Brachiosaurus and scavengers of dead Brachiosaurus. The largest theropods of the Morrison, Torvosaurus and Saurophaganax may have been capable of taking larger prey, and thus may have been the biggest threats to Brachiosaurus. However, even these giant predators likely wouldn’t have dared to attack a healthy adult Brachiosaurus, which may have weighed as much as 12 times their weight. Adult Brachiosaurus were truly in a league of their own. If an individual survived long enough, there wouldn’t have been a predator around that could take it down, nor any animal that it couldn’t look down upon. In the world of Brachiosaurus, the only things taller were the trees.

Extinction and Legacy. Brachiosaurus lived toward the end of the Jurassic and may have gone extinct along with much of the other Jurassic fauna as the continents continued to separate, climate changed, and ecosystems shifted. However, Brachiosaurus is mostly known from the Kimmeridgian about 155-153 Ma, slightly older than the very end of the Jurassic (the Tithonian age). It is unclear if it survived until the end of the Jurassic, or if it went extinct a bit before the rest of its ecosystem. Brachiosaurus was comparatively rare, possibly due to the rarity of giant trees (like redwoods) in the Morrison, compared to the abundance of such trees elsewhere where other brachiosaurids, like Giraffatitan thrived. Perhaps Brachiosaurus went extinct because the Morrison was simply not as well suited to a brachiosaurid as other environments. However, this may not be entirely accurate as related Brachiosaurids including Abydosaurus and Sonorasaurus did inhabit North America in the Early Cretaceous. Whenever and whatever caused Brachiosaurus’s extinction, it is alive and well in the minds of human beings today. It was discovered during a period of public fascination with sauropods due to their large size, and Riggs was able to play into this public sentiment very effectively when he announced his Brachiosaurus, which was one of the largest dinosaurs yet found. Brachiosaurus has appeared in numerous movies and television shows, including the 1999 BBC documentary Walking with Dinosaurs, Disney’s Dinosaur (2001), and most famously, the Jurassic Park Franchise, with its first appearance in the latter being its iconic scene in 1993’s Jurassic Park, being the first dinosaur the characters see in the park. The holotype of Brachiosaurus resides in the Field Museum of Natural History in Chicago, IL, USA. A complete skeletal reconstruction that was once on display at the field museum can now be seen welcoming travelers in Chicago’s O’Hare Airport. Other museums also have Brachiosaurus material on display, including The Museum of Ancient Life at Thanksgiving Point in Lehi, UT, USA, which has another full skeletal replica of Brachiosaurus along with part of Brigham Young University’s Dry Mesa Quarry Brachiosaurus remains.