Paleo Profiles: Brachiosaurus

Today on Paleo Profiles we're looking at one of the best known dinosaurs to ever walk the face of the planet: Brachiosaurus. When first discovered it was described as being 'the largest known dinosaur' and is one of the dinosaurs which come to mind when we think of the prehistoric reptiles. One of the most iconic scenes in Jurassic Park featured the Brachiosaurus - when we first fully see a dinosaur. However, quite ironically our image of the Brachiosaurus over the last decade has been shown to be inaccurate - another dinosaur for almost a century believed to be Brachiosaurus was used for reconstructions.

Discovery and Fossils

An excavator next to the humerus of a Brachiosaurus

Dentist and amateur collector Stanton Merill Bradbury wrote to palaeontologists believing that he had found signs of dinosaur fossils. He struck up a conversation with one in particular - Elmer Riggs - who believed they were more likely to be mammal fossils from the Eocene, a time not too long after the dinosaurs went extinct. Going out to Colorado in 1900 he discovered something far bigger than any mammal to walk the land. During excavation they happened upon the humerus which was so long that Riggs thought it be to a deformed femur - the longest bone in the body. He quickly surmised that the bones were from a group of dinosaurs called sauropods - large herbivorous dinosaurs characterised by long necks and tails. At first he believed it to be an Apatosaurus but looking at the ribs realised it was a new animal. Due to the length of the femur and the size of the animal's chest he named it Brachiosaurus altithorax - 'Arm lizard of deep chest' - in 1903. The specimen wasn't complete - it lacked a head for one - but other specimens were discovered. In 1914 German palaeontologist Werner Janensch found several specimens from the Tendaguru Formation in what is now Tanzania which he described as being two new species of Brachiosaurus - B. altithorax and B. fraasi. However, since then, as well as another one from Portugal and a much younger specimen, they have been separated into a new genus entirely. The African species were reclassified as Giraffititan and most reconstructions were based on Giraffatitan before it was known to be distinct.

We have discovered several different specimens of Brachiosaurus since the initial one in 1900. However, they are far from complete, and it is only because of how closely Brachiosaurus resembles its African cousin that we picture what it looked like. In fact, the most complete specimen that we have is from a sub-adult so it died before all of its bones could fuse together. In 2012 in Wyoming a 2-metre long skeleton missing a skull was discovered, and for some time was it was initially thought to be a diplodocid. In 2018 a foot was discovered, the largest to be discovered in the region, in Wyoming but missing the femus - it is thought to be the largest Brachiosaurus discovered based on the foot's size.

Biology

Femur (left) and the humerus (right) of a Brachiosaurus

As mentioned Brachiosaurus was a sauropod which were some of the largest land animals to ever exist - a giant named Patagotitan weighed the same as 10 African elephants. Brachiosaurus was a giant in both height and weight. With what fossil evidence we have it is very difficult to estimate how much one weighed so we have results varying from 28 metric tons to a staggering 58 tons! To put it in perspective, the smallest estimate will put Brachiosaurus as weighing the same as four and a half bull African elephants. Sauropods normally had long tails to act as a counterbalance their long necks so Brachiosaurus had a shorter but muscly tail - about 7 metres in length. A large part of this is due to the dinosaur's neck posture - although long it was held in an S-pose or at an angle. Past depictions in museums, which continue in popular media, try and portrayed extinct animals as large as they could, so Brachiosaurus was portrayed holding its long neck directly upwards. Instead, it likely would have held it at a slight angle in the same way that giraffes do. From snout to tail the Brachiosaurus was around 26 metres long. Due to their size it was once believed that sauropods were aquatic using the water to support their immense size - Elmer Riggs argued against this when he described the Brachiosaurus. The theory has, for a very longtime, been disproved - if anything the water could have crushed the dinosaur's chest.

A Giraffatitan in the Berlin Natural History Museum

Most of what we know about Brachiosaurus comes from what we know about Giraffatitan. Luckily, several important parts of the dinosaur is known. The arms were exceptionally long, the humerus was longer than the femur causing confusion for Riggs, making the shoulders very high. This allowed Brachiosaurus to be like a giraffe and browse from the tops of trees. Like many other sauropods the feet were wide, mostly for balance, but they could also be used for communication. Elephants make rumbles which humans cannot detect which travel along the ground - their wide feet pick up these rumbles. Quite possibly sauropods did so as well. How did such a large animal function? Steven Perry and Christian Reuter have hypothesised what types of lungs the dinosaur would have, and they believed that one found in birds would be the best. In 2016 Mark Hallett and Mathew Weddel used Brachiosaurus to find how sauropods managed to breathe. Instead of acting like a bellows, as in our lungs, birds have 'air sacs' where one pumps in air and another pumps waste out allowing quick air exchange. Sauropods had openings in their bones to allow air sacs to sit in and pump the oxygen to their muscles. As we discover more fossils we have begun to understand that all dinosaurs were closer to birds than crocodiles - before the discovery of the air sacs it was thought that if it was warm-blooded Brachiosaurus would overheat. Air sacs also served to cool the body so they were likely endothermic and homeothermic. 

A reconstructed skull in the Denver Museum of Nature and Science

Finally, we get to the skull - the most iconic and yet dubious part of the dinosaur. We only have a partial skull and most reconstructions are based on Giraffatitan. There were enough distinctions between the two skulls, however, to present evidence that they were distinct. The skull was small for its size - so small, in fact, that Fabien Knoll and Daniel Schwarz-Wings believed that they could not accurately work out the animal's intelligence. A key feature of the skull is the crest and there have been various theories about what its use was. One major theory is that these crests were where the nostrils were located; as the animal drank it could keep its nostrils out of the water. Another theory has been suggested that they were really a resonating chamber for communication. Finally, we have the dinosaur's teeth. These chisel-shaped teeth were replaced across the animal's life, and would nip off vegetation. Brachiosaurus could not chew - instead it had to slice through vegetation with its very muscular jaws and leave the rest to ferment in its gut. Due to that it had to eat a lot - possibly up to 400 kg of foliage a day.

When and Where

Brachiosaurus lived around 154 million years ago in the Jurassic period - in the original Jurassic Park it is one of two dinosaurs to appear on-screen which actually came from the Jurassic. The supercontinent Pangea had started to break apart, most of the world was humid, and the air was rich in oxygen. Brachiosaurus was found in the Morrison Formation - perhaps the most famous dinosaur fossil formation, tied with the home of the Tyrannosaurus Hell Creek. Today it covers a huge area of the US; most of it is in Colorado and Wyoming with outreaches into Montana, North and South Dakota, Nebraska, Kansas, and even parts of Oklahoma and Texas. The Great Hall of Dinosaurs at Yale's Peabody Museum even has a mural by Rudolph Zallinger entitled The Age of Reptiles mostly depicts the inhabitants of Morrison Formation. The Morrison Formation was made of semiarid most of the year with the exception of the wet seasons - floodplain prairies and riverine forests were where Brachiosaurus could be found.

Neighbours

Zallinger's now outdated mural depicting some of the Morrison Formation dinosaurs

The Morrison Formation was rich in dinosaur life. Brachiosaurus was far from the only sauropod - Diplodocus, Camarasaurus, Apatosaurus, Brontosaurus, and Barosaurus were just some of the sauropods to call Morrison Formation their home. Brachiosaurus likely filled the same role as a giraffe; competition with other sauropods would drive it to reach the top of the trees, out of the way of the shorter sauropods. Other herbivores lived alongside the sauropods including nimble Dryosaurus and the formidable Stegosaurus. An adult Brachiosaurus had few natural predators - much like an elephant they were too big to attack without injury. However, younger ones had several potential predators. The horned Ceratosaurus, giant Torvosaurus and Saurophaganax, and the 'Lion of the Jurassic' Allosaurus all could prove deadly for a growing Brachiosaurus. As the Morrison Formation had floodplains and rivers which could easily burst their banks or flood the land during the wet season. These flash floods could easily drown helpless dinosaurs, and these floods help preserve their fossils. As a result, we know quite a bit about fauna in Jurassic Colorado and Wyoming, and every year we make new discoveries. 

Thank you for reading. The sources I have used are as follows:

-Gregory S. Paul, The Princeton Field Guide to Dinosaurs, Second Edition, (Princeton: Princeton University Press, 2016)

-Steve Brusatte, The Rise and Fall of the Dinosaurs: The Untold Story of a Lost World, (London: Macmillan, 2018)

-Mark Hallett and Mathew Wedel, The Sauropod Dinosaurs: Life in the Age of Giants, (Baltimore: Johns Hopkins University Press, 2016)

-'Brachiosaurus', Prehistoric-wildlife.com, [Accessed 06/02/2019]

-'Giraffatitan', Prehistoric-wildlife.com, [Accessed 06/02/2019]

-E.S. Riggs, 'Brachiosaurus altithorax, the largest known dinosaur', American Journal of Science, 4:15, (1904), 299-306

-Micahel Taylor, 'A Re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and Its Generic Separation from Giraffatitan brancai (Janensch 1914)', Journal of Vertebrate Paleontology, 29:3, (2009), 787-806

-Steven Perry and Christian Reuter, 'Hypothetical Lung Structure of Brachiosaurus (Dinosauria: Sauropoda) Based on Functional Constraints', Fossil Record, 2:1, (1999), 75-79

-Fabian Knoll and Daniela Schwarz-Wings, 'Palaeoneuroanatomy of Brachiosaurus', Annales de Paléontologie, 95, (2009), 165-175

-Anthony Maltese, Emanuel Tschopp, Femke Holwerda, and David Burnham, 'The real Bigfoot: a pes from Wyoming, USA is the largest sauropod pes ever reported and the northern-most occurrence of brachiosaurids in the Upper Jurassic Morrison Formation', PeerJ, 6, (2018)

Thank you for reading. As this is a hobby of mine, not my speciality, if you feel that I have got something wrong or have omitted something please mention it in the comments. For other Paleo Profiles please see our list. For future blog updates please see our Facebook or catch me on Twitter @LewisTwiby.