CMC VP 7180 mount
Allosaurus fragilis • “Different lizard, fragile”
The most common and lethal apex predator of the Late Jurassic Morrison Formation, hunting with gaping jaws, slashing bites, and robust three-clawed forelimbs.
FMNH P 25107 mount
Brachiosaurus altithorax • “Arm lizard with high chest”
A colossal macronarian sauropod with disproportionately long forelimbs and an elevated neck built for high-canopy conifer browsing during the Late Jurassic.
Allosaurus fragilis and Brachiosaurus altithorax were both Jurassic dinosaurs. Fossils of both species have been discovered within the Morrison Formation, demonstrating that they lived during overlapping geological intervals and shared the same ancient regional environment. Allosaurus fragilis was an adapted carnivore, whereas Brachiosaurus altithorax was a herbivore, representing fundamentally distinct ecological roles. Based on available fossil estimates, Brachiosaurus altithorax was larger than Allosaurus fragilis in both overall length and estimated body mass (approximately 17.5× heavier and 3.06× longer). Estimates vary between individual specimens.
Anatomical dimensions compared on a shared proportional baseline against an adult human (1.8 m / 5.9 ft).
Brachiosaurus altithorax was longer by approximately 17.5 m.
Brachiosaurus altithorax stood taller by approximately 9 m.
Brachiosaurus altithorax had a greater estimated mass by 33 tonnes.
Based on available fossil estimates, Brachiosaurus altithorax was larger than Allosaurus fragilis in both overall length and estimated body mass (approximately 17.5× heavier and 3.06× longer). Estimates vary between individual specimens.
Paleontological Note on Mass Estimates: Dinosaur body weights are derived through volumetric laser scanning and femoral circumference scaling equations. Because soft tissue does not fossilize directly, mass values carry statistical margins of uncertainty and represent scientific estimates rather than exact weights.
Direct answers to the most important comparative questions about how these two prehistoric species differed.
Based on available fossil estimates, Brachiosaurus altithorax was larger than Allosaurus fragilis in both overall length and estimated body mass (approximately 17.5× heavier and 3.06× longer). Estimates vary between individual specimens.
Allosaurus fragilis was an adapted carnivore, whereas Brachiosaurus altithorax was a herbivore, representing fundamentally distinct ecological roles.
Allosaurus fragilis lived during the Jurassic (Late Jurassic, 155–145 Ma), while Brachiosaurus altithorax lived during the Jurassic (Late Jurassic, 154–150 Ma).
Fossils of Allosaurus fragilis were recovered from Western United States (Morrison Formation), Portugal, whereas Brachiosaurus altithorax was discovered in Colorado, Utah, Wyoming (Morrison Formation).
Allosaurus fragilis had a bipedal locomotion, contrasted with Brachiosaurus altithorax which had a quadrupedal stance.
Their recorded fossil ranges overlap by approximately 4 million years (between 154 and 150 Ma). This demonstrates that Allosaurus fragilis and Brachiosaurus altithorax existed on Earth during the same geological epoch. However, chronological coexistence does not automatically prove they shared the exact same localized ecosystem, hunted one another, or directly interacted.
Side-by-side catalog of verified anatomical measurements and geological records.
| Scientific Parameter | A Allosaurus fragilis | B Brachiosaurus altithorax |
|---|---|---|
| Scientific Binomial | Allosaurus fragilis | Brachiosaurus altithorax |
| Name Meaning | “Different lizard, fragile” | “Arm lizard with high chest” |
| Taxonomic Clade / Group | Theropods | Sauropods |
| Geological Period | Jurassic | Jurassic |
| Fossil Time Range | Late Jurassic, 155–145 Ma | Late Jurassic, 154–150 Ma |
| Diet & Trophic Guild | Carnivore | Herbivore |
| Maximum Length | 8.5 m (27.9 ft) | 26 m (85.3 ft) |
| Standing / Hip Height | 3 m (9.8 ft) | 12 m (39.4 ft) |
| Estimated Body Mass | 2 tonnes (2,000 kg) | 35 tonnes (35,000 kg) |
| Locomotion / Stance | Bipedal | Quadrupedal |
| Geographic Localities | Western United States (Morrison Formation), Portugal | Colorado, Utah, Wyoming (Morrison Formation) |
| Geological Formation | Morrison Formation, Lourinhã Formation | Morrison Formation |
| Discovery History | Historical holotype | Historical holotype |
Visualizing both species across the 186-million-year span of the Mesozoic Era.
Their recorded fossil ranges overlap by approximately 4 million years (between 154 and 150 Ma). This demonstrates that Allosaurus fragilis and Brachiosaurus altithorax existed on Earth during the same geological epoch. However, chronological coexistence does not automatically prove they shared the exact same localized ecosystem, hunted one another, or directly interacted.
Comparing the rock strata, paleoclimates, and ancient landscapes where their fossils were entombed.
Western United States (Morrison Formation), Portugal
North America
Colorado, Utah, Wyoming (Morrison Formation)
North America
Stratigraphic Synthesis:
Direct comparisons between extinct animals are inherently shaped by the incomplete nature of the fossil record. Skeletal dimensions reflect holotype or well-preserved paratype specimens, but individual ontogenetic age, sexual dimorphism, and intraspecific variation all influence the true living size of any prehistoric animal.
Body mass estimates shown above represent calculated averages from published volumetric models and biomechanical limb scaling. As modern synchrotron imaging and 3D digital skeletal mounts advance, museum measurements are continually refined.