Brachiosaurus

There are some dinosaurs that everybody thinks of when they hear the word “dinosaur”. Among these is a very large sauropod which was the reptilian analog of a giraffe. I am, of course, talking about Brachiosaurus.

Brachiosaurus is one of the more famous dinosaurs. This animal was the iconic “giraffe of the Jurassic”, and for a while it held the record of being the largest dinosaur known. It has been featured in countless books and TV documentaries about dinosaurs, and got a major role in the 1993 movie Jurassic Park. But how much do we really know about it?

Brachiosaurus makes its debut appearance in Jurassic Park (1993).

Considering that Brachiosaurus is one of the more familiar dinosaur names, we actually know surprisingly little about it. This largely has to do with the fact that fossils of this animal are extremely rare. Our total knowledge about this animal’s anatomy comes from bits and pieces of several skeletons that were found here and there across much of the Rocky Mountains within the states of Wyoming, Utah, and Colorado, as well as one location in the extreme westernmost parts of the Oklahoma pan-handle. That’s it.

Map of locations where Brachiosaurus fossils have been found, as of 2020:
1) KU Quarry, Wyoming (KUVP 129724; KUVP 133862; KUVP 142200; KUVP 144767)
2) Freeze-out Hills, Wyoming (one caudal vertebra, undescribed)
3) Reed’s Quarry 13, Wyoming (undescribed specimen)
4) Jensen/Jensen Quarry, Utah (FHPR 17108)
5) Fruita, Colorado (undescribed specimen)
6) Riggs’ Quarry 13, Colorado (FMNH P 25107) (this is the holotype)
7) Dry Mesa Quarry, Colorado (BYU 9462; BYU 12866; BYU 12867; BYU 13023)
8) Potter Creek, Colorado (BYU 4744; USNM 21903)
9) Felch Quarry 1, Garden Park, Colorado (USNM 5730)
10) Kenton Pit 1, Oklahoma (OMNH 01138)

The discovery of Brachiosaurus dates back to the very beginning of the 20th Century. In 1900, a few very large bones were discovered in western Colorado near the small town of Fruita, located only a short distance away from the Utah-Colorado border. There wasn’t much to go on: some vertebrae, one hip bone, one femur, one humerus, and part of the shoulder. Still, the bones were distinctive enough from other sauropod dinosaurs known from the Morrison Formation to warrant classifying it as a new genus. In 1903, the creature was officially named Brachiosaurus altithorax, “arm lizard with a wide chest” by Elmer Riggs.

In 1909, a German paleontological expedition led by Wilhelm von Branca were exploring in the German colony of Tanzania when they discovered some large bones near a site called Tendaguru, meaning “steep hill” in the Mwera language. Excavations revealed that it was a partial skeleton, and similarities were soon observed between these bones and the bones that had been unearthed by Elmer Rigg’s team in Colorado several years earlier. In 1914, these bones were classified as another species of Brachiosaurus, named Brachiosaurus brancai. It helped that there was a lot more of the skeleton in this specimen, and for decades afterwards, the African species of Brachiosaurus served as the model for the North American species. However, beginning in the 1980s, doubts arose whether these animals were, in fact, two species of the same genus. A thorough compare-and-contrast analysis showed that there were actually more differences noted in each bone than similarities. Consequently in 1988, the African species was re-named as Giraffatitan brancai.

Both genera had similarities. Both Brachiosaurus and Giraffatitan were very large animals, both of them belonged to the sauropod group known as “Macronaria”, both of them had necks which could be held vertically or near-vertically rather than the horizontally-oriented necks of many other sauropods, both of them had arms which were longer than their legs (hence Brachiosaurus‘ name) which resulted in high shoulders and the back sloping downwards towards the hips, and the neck was longer than the tail. Now that we have established what they had in common with each other, how different was Brachiosaurus from Giraffatitan? Since neither skeleton is complete, and in fact Brachiosaurus is known from scant remains, it is impossible to do a comprehensive 100% compare-and-contrast analysis of both of their skeletons. However, based upon the remains which we do have, we can draw a few conclusions.

First, it appears that either A) Giraffatitan was larger, or B) Both animals were the exact same length but Giraffatitan was more physically massive. Brachiosaurus is estimated to have reached a length of 70 feet long or thereabouts with a 30 foot neck. By contrast, Giraffatitan may be the same length, but differences in body proportions (which I will describe later) meant that it was bulkier than its North American counterpart. Other estimates state that Giraffatitan exceeded Brachiosaurus in size, measuring 75 to 85 feet long.

Second, the skull shape was different. When most people imagine what the head of a Brachiosaurus looked like, they are actually imagining the head of a Giraffatitan, with its high firefighter-helmet crest. Only one partial skull of a Brachiosaurus has been found near Garden Park, Colorado; it was found in 1883, but it wasn’t identified as belonging to a Brachiosaurus until decades later. Although the skull is not complete, enough of it was preserved to indicate that it was not as tall as the skull of Giraffatitan. It appears to have had a much lower crest, sort of in-between the low curvaceous skull of an Apatosaurus and the tall crested skull of a Giraffatitan.

Skulls of Brachiosaurus altithorax (A) and Giraffatitan brancai (B). Carpenter, Kenneth; Tidwell, Virginia (1998). “Preliminary description of a Brachiosaurus skull from Felch Quarry 1, Garden Park, Colorado”. Modern Geology, volume 23. Page 73 (Pages 69–84).

Third, Brachiosaurus had larger and bulkier shoulders compared to Giraffatitan, despite the fact that Giraffatitan seems on the whole to have been larger and more robustly-built than Brachiosaurus. However, Brachiosaurus might (emphasis on “might”) have had a wider chest than its African counterpart.

Fourth, Brachiosaurus may have had a longer chest compared to Giraffatitan. This cannot be stated with 100% certainty because we have not yet found a complete vertebral column or a complete ribcage of Brachiosaurus which could give us a clear picture of the animal’s body proportions. However, if it is true that Brachiosaurus had a longer torso, it would mean that its back would have had a much gentler slope than its African counterpart.

Fifth, Brachiosaurus might have had a longer tail. Only one tail vertebra of Brachiosaurus has been found so far. However, based upon its features, it has been hypothesized that the tail would have been substantially longer than that of Giraffatitan.

The scarcity of remains hints that Brachiosaurus might have been a rare animal out on the Jurassic plains. Other sauropods such as Camarasaurus were far more common.

Like Camarasaurus, Brachiosaurus was a member of a group of sauropod dinosaurs called the “macronarians”, meaning “the large nostrils”. The skull likely acted as a resonating chamber, able to produce loud low frequency long-range noises, which would be very helpful for communicating over the vast expanses of the Morrison Formation plains. If it is true that Brachiosaurus was rare, or perhaps even a solitary animal by nature, it would still need to communicate with other members of its kind, especially during the mating season. Being able to produce such sound, which could travel over long distances, would help these animals to communicate with each other even if individuals were located miles apart from one another.

Unlike the diplodocid sauropods of the Morrison Formation such as Apatosaurus, Barosaurus, and Diplodocus, Brachiosaurus did not hold its neck in a horizontal position. Instead, it held its neck either vertically or at a diagonal angle. The act of the head sticking far above the ground would minimize the chance that the sounds that it produced would be broken up and dissipated due to ground clutter, such as rocks, trees, and even other dinosaurs. This head attached to a long vertical neck would act like a submarine’s periscope, enabling it to see for long distances, and also enabling other members of its kind to spot it from a long distance away. To make sure that it could be seen from long distances away, it is possible that the head and the neck were very brightly and vividly colored while the rest of the body was comparatively drab. It’s also possible that the head might have sported some type of decoration to further ensure that it could be spotted from miles away by other members of its species – perhaps a frill or a mane of quills or baleen-like bristles. However, color and adornment are only hypothetical conjecture and should not be taken as fact.

Below are a pair of drawings that I made of Brachiosaurus altithorax. I have adorned the top part of the neck with a series of long quills forming a mane, and I also made its head bright red in order to stand out amidst the Morrison landscape. As to the remaining colors of grey with blue stripes, I based this on the Brachiosaurus model made for the Carnegie Collection in the 1980s. The drawings were made with No. 2 pencil, No. 3 pencil, and assorted Crayola and Prismacolor colored pencils.

Brachiosaurus altithorax. © Jason R. Abdale (April 26, 2021).

Keep your pencils sharp, everyone.



Categories: Paleontology, Uncategorized

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