Brontosaurus and Brachiosaurus fit the standard characteristics of a sauropod dinosaur, with their long, massive necks, small heads, robust bodies and herbivorous diets. Due to their similar morphology and behavior, the two are easily confused with each other.
How is Brontosaurus different from Brachiosaurus?
The main difference between a Brontosaurus and a Brachiosaurus is observable in their size, posture, and feeding habits – among some other traits. Brontosaurus is longer on average and adopts a more low-leaning neck position to graze on low vegetation, while Brachiosaurus is taller and much heavier, with an upright neck and taller forelimbs to browse leaves on tall trees, and a shorter tail.
What is a Brontosaurus?
The Brontosaurus genus contains three species: B. excelsus, B. yahnahpin, and B. parvus. As with other sauropods in the Diplodocidae family, they were among the longest dinosaurs in the Earth’s history, owing to their long necks and tails, relatively slender builds, and short legs.
Brontosaurus had short and stumpy legs in contrast to their elongated and low-lying necks, earning them the title of the “dachshunds” among other giant dinosaurs. The dinosaur’s tail’s length and unique structure allowed it to be used as a whip.
Their teeth were long and lean, terminating into a blunt triangle-shaped point, suggesting that Brontosaurus fed primarily by stripping leaves off of branches with their rows of teeth.
What is a Brachiosaurus?
Brachiosaurus is a genus with currently only one type species: B. altithorax. It belongs to another sauropod family to which it has lent its name: Brachiosauridae. As with other members of this family, the Brachiosaurus is prominent for being very large.
While their necks were long by themselves, they were distinctly inflexible in side-to-side movement, while being flexible vertically, resulting in a neck posture that was higher and more upright.
Brachiosauruses had pronouncedly taller forelimbs compared to other sauropods, leading them to adopt a giraffe-like gait.
Their teeth, as with other Brachiosauridae species, were thick and broad, and likely enabled them to cut through food rather than scrape them off of trees.
Differences between Brontosaurus and Brachiosaurus
Physical Measurements
Brontosaurus had a longer body than a Brachiosaurus’; in contrast, the Brachiosaurus was taller and significantly heavier.
The Brontosaurus’ type species, B. excelsus, is estimated to span roughly 22 meters from head to tail, with a weight of approximately 15 tons (13.6k kg) and a height of 8.5 m.
Brachiosaurus owes its taller stature to its upright neck: paleontologists believe it stood as tall as 9.4 meters, with a length of 18-21 m. It had a prodigious mass for any dinosaur; its weight is reported to be around 35 metric tons (35k kg).
Neck Posture
Observing the silhouette or assembled skeleton of a Brontosaurus and Brachiosaurus reveals one distinct difference – the Brontosaurus had a neck that leaned lower and closer to the ground, and was somewhat shorter. Its neck bones had paired spines to support the colossal structure.
Meanwhile, the Brachiosaurus held its larger and longer neck high, similar to the posture of a modern giraffe. Their cervical (neck) vertebrae allowed them to angle and lift their heads up more easily to graze at tall treetops.
Limbs and Gait
Brontosaurus forelimbs were actually slightly shorter than their hind legs, and as a result, their vertebrae sloped downward as it reached the neck.
Alongside other diplodocids, the Brontosaurus has earned the affectionate nickname of the “dachshund” among other giant dinosaurs due to their short limbs.
In comparison, the forelimbs of a Brachiosaurus were longer than the rear limbs, and likewise supported much more of their body weight. This allowed them to stride farther, although scientists believe it also caused them to walk unevenly.
Teeth
Brachiosaurus teeth were tough and broad, resembling spoons or spatulas. The structure of their teeth allowed them to cut away at plant parts and chew foliage more efficiently compared to other sauropods.
This is in sharp contrast with diplodocids like Brontosaurus, whose teeth were the shape of pencils or pegs – long, slender, with blunt triangular ends. This comb-like arrangement suggests that Brontosaurus was unable to tear away tough plant material, and instead ate by scraping the foliage off of branches.
Period
Both Brachiosaurus and Brontosaurus lived in the same temporal range – they existed during the Late Jurassic Period from its Kimmeridgian to its Tithonian stages.
Evidence suggests that Brachiosaurus dinosaurs existed between 154 to 150 million years ago. In contrast, traces of Brontosaurus have been discovered over a slightly longer range, from 156 to 146 million years ago.
Feeding Habits
The two dinosaurs were obligate herbivores, eating a diet that consisted solely of the flora available at the time, with a few subtle differences.
The Brachiosaurus’ taller stature, vertically flexible and upright necks, and taller forelimbs enabled it to feast on the foliage found atop treetops and high places. Its broad and durable teeth also cut through plants entirely, breaking up chunks of the food to eat.
Brontosaurus had a more horizontal neck posture, which was better suited for the consumption of low-lying vegetation, although its height meant it could also eat from some trees and tall areas.
Neither dinosaur chewed their food. They took in gizzard stones (gastroliths) to grind down tough and fibrous plant parts.
Social Behavior
Many sauropods preferred to travel in large herds – Brachiosaurus is no exception, as scientists theorize that the large herbivore roamed alongside members of its own species. Together, Brachiosaurus herds would feast on all the vegetation in an area and move on to another location once their food supply was exhausted.
In stark contrast, it is believed that the Brontosaurus was a much more aloof herbivore that occasionally traveled in herds but largely kept to itself while eating.
Habitat and Range
The Brachiosaurus and Brontosaurus shared the historically semiarid region known as the Morrison Formation, which currently contains the most fertile grounds for dinosaur remains in North America.
Although Brontosaurus remains have only been found within the Morrison, incomplete Brachiosauridae fossils have been retrieved from other countries, including Algeria, Portugal and Tanzania.
Naming
Due to their long forelimbs, the American paleontologist, Elmer S. Riggs, described the fossils retrieved from the Colorado River valley as belonging to a dinosaur that he christened with the name Brachiosaurus (βραχιων σαυρος), which was Greek for “arm lizard.”
Brontosaurus was likewise named by the U.S. paleontologist Othniel Charles Marsh, from the Greek words for “thunder lizard” (βροντη σαυρος).
Species
Three Brontosaurus species are known: B. excelsus, B. yahnahpin and B. parvus. Of this trio, B. excelsus acts as the type species, is the largest, and the first to be discovered.
Brachiosaurus currently consists of only one species: B. altithorax, the type species. The genus used to contain B. brancai, although the species has since been reclassified as Giraffatitan brancai, while a third presumptive species was moved to its own genus, Lusotitan.
Comparison Chart: Brontosaurus vs Brachiosaurus
| Areas | Brontosaurus | Brachiosaurus |
| Physical Measurements | Longer; 22 m long, 8.5 m tall, 13.6k kg | Taller and heavier; 18-21 m long, 9.4 m tall, 35k kg |
| Neck Posture | More horizontal and low-leaning | Upright |
| Limbs and Gait | Shorter forelimbs | Longer forelimbs, uneven gait |
| Teeth | Long, slender, pencil-shaped | Tough, broad, spatula-shaped |
| Period | Late Jurassic | Late Jurassic |
| Feeding Habits | Ate low-lying vegetation | High browsing herbivore |
| Social Behavior | Solitary | Ate and traveled in large herds |
| Habitat and Range | Morrison Formation, North America | Ditto; Algeria, Portugal, Tanzania |
| Naming | Greek: “Thunder lizard” (brontē sauros) | Greek: “Arm lizard” (brachion sauros) |
| Species | 3 | 1 |
How are Brontosaurus and Brachiosaurus similar?
By virtue of being sauropods, Brontosaurus and Brachiosaurus enjoy many of the same adaptations to their physiology, feeding habits and other traits.
Apart from their characteristically-long necks and small heads, they both stuck to a diet of foliage and other plant parts. These hulking dinosaurs would have needed to graze frequently to sustain their large bodies.
Brachiosaurus and Brontosaurus occupied the same temporal range and habitat, living together in the exact same stages of the Late Jurassic Period as inhabitants of the Morrison Formation in North America.
FAQ
Did sauropods live in the water?
There has been a long-standing belief that sauropods were partially-aquatic creatures that lived in water to lessen the burden of moving their hulking bodies, with their long necks apparently helping them keep their heads above water.
Modern consensus, however, agrees that sauropods lived entirely in terrestrial ecosystems. They wouldn’t have even waded into ponds.
Scientists beginning in the 1960s’ “Dinosaur Renaissance” proved that sauropod bodies were strong and sturdy enough to support themselves on land, and that many of their “aquatic” adaptations, such as large “nostrils,” hollow bones, and air sacs, served entirely different roles.
How did Brachiosaurus defend itself?
As with other sauropods, especially its cousin Brontosaurus, the Brachiosaurus dinosaur would have been large enough to repel most predators: even the largest carnivores at the time, such as Allosaurus, were barely half its size.
Should the Brachiosaurus find any threats, its primary defensive weapon would be its long tail, which it would have used like a whip, similar to Brontosaurus. However, its tail was shorter relative to other sauropods, and would have less range.
Their skin was also tough and leather-like, although it would still be penetrable to the sharp teeth of smaller theropods.
Conclusion
The key differences between Brontosaurus and Brachiosaurus involve physical features, such as variations in size and structure in their neck and limbs; as well as certain behavioral traits.
Brontosaurus specimens were longer and leaner, with larger tails and shorter necks that leaned more horizontally; forelimbs that were short compared to their rear legs; and pencil-like teeth. They fed by scraping foliage off of low-lying vegetation, and lived largely by themselves.
The Brachiosaurus was taller and much heavier, possessing shorter tails and longer and wider necks that stood upright, allowing them to graze on treetops and high areas, cutting away at resistant plant materials with tough teeth shaped like spatulas. Their forelimbs were taller than their hind legs. Furthermore, they were more social, and lived among large herds.
Both dinosaurs likely encountered each other, as they existed together in the Late Jurassic Period within the dinosaur fossil hotspot of the Morrison Formation of North America.
