“The Dominant Predator of the Jurassic West”
Binomial Allosaurus fragilis · AL-oh-SOR-us
Late Jurassic · 155-145 Ma
IllustrationAllosaurus fossil records in Fossil Atlas are mapped as selected modern discovery locations, with 205 source-backed records currently shown. Known especially from the Morrison Formation of the western United States, with additional reported Jurassic records from Portugal. Key mapped formations in the current dataset include Morrison Formation, Morrison Fm, Morrison. These pins are fossil record locations, not a complete ancient habitat map.
Allosaurus was a large meat-eating theropod from the Late Jurassic and the apex predator of the Morrison Formation, the rock unit that records the classic western North American Jurassic ecosystem of giant sauropods and stegosaurs. Its fossils are among the most abundant of any large theropod, which is why it is so well understood. Mapped records mark modern discovery sites, not the full extent of its ancient range.
Drawn true to scale on a metre ruler.
Length
measured8.5 m · 28 ft
Largest known specimens
Height
measured3.2 m · 10.5 ft
Body mass
estimate2,000 kg · 4,400 lb
Typical adult
Top speed
estimate34 km/h · 21 mph
Modelled, debated
Bite force
estimate3,500 lbf
Teeth
measured≈ 70
Brain : body (EQ)
estimate1.5
Encephalization quotient
Allosaurus was the apex predator of the Morrison Formation for most of the Late Jurassic. Its skull was lighter and more flexible than a tyrannosaur's, built for a different style of attack: opening wide and driving the upper jaw downward into prey rather than biting and holding. Multiple individuals found in bonebeds have prompted discussion of group behavior, though whether this reflects social hunting or animals drawn to the same carcass is unresolved.
The skull
Light and fenestrated with large openings, allowing a wide gape. The upper jaw moved somewhat independently of the braincase, amplifying the downward striking force.
Feeding
Blade-like, serrated teeth well suited for slicing flesh. Wear patterns and skull mechanics suggest a different feeding style from later large tyrannosaurs.
Bonebeds
Cleveland-Lloyd Quarry in Utah has produced over 70 Allosaurus individuals from a single site, one of the most studied large predator assemblages in the record. Why so many ended up together is still debated.
Size
Typically 8-9 metres, with some individuals estimated larger. Not as heavy as the biggest Cretaceous predators, but well-matched to the largest Morrison prey animals.
Position of this animal’s known range across 252 million years of the Mesozoic and beyond.
155-145 million years ago
Allosaurus is one of the anchor predators of the Morrison Formation.
Several Morrison quarries preserve multiple Allosaurus individuals.
Its skull was lighter and more flexible than a tyrannosaur skull.
Allosaurus shared Morrison ecosystems with Stegosaurus and several large sauropods.
Marsh described Allosaurus in 1877 from Colorado material collected during the Bone Wars. The Cleveland-Lloyd Quarry, excavated repeatedly from the 1920s onward, has yielded more Allosaurus material than any other single site. That assemblage has driven much of what researchers know about its growth, variation, and ecology. The reason so many individuals ended up at the same location, whether it was a predator trap, a drought-related die-off, or something else, has not been settled.
Animals known from the same deposits and time as Allosaurus.
Stegosaurus
A heavily defended contemporary whose tail spikes carry healed puncture evidence directly matching an Allosaurus vertebra.
Diplodocus
One of the long-necked sauropods Allosaurus likely hunted or scavenged, particularly targeting juveniles.
Ceratosaurus
A smaller, horned theropod sharing the same predator niche at a lower body size, probably avoiding direct competition with adult Allosaurus.
Other members of Allosauridae.
Carcharodontosaurus
A giant Cretaceous relative from North Africa in the same broader allosauroid group.
Giganotosaurus
A South American carcharodontosaurid, among the largest theropods known, sharing an evolutionary lineage with Allosaurus.
Sinraptor
A Chinese Jurassic allosauroid showing the family spread across the ancient world during the same period.
Pins show selected fossil records for Allosaurus; use them as modern discovery evidence, not a complete range map. Modern fossil discovery map: pins show where selected fossil and specimen records were found today, not ancient Earth positions. What does this mean?
Specimen evidence
These are sourced specimen assets, separate from reconstruction artwork. Only media with clear open or reusable rights is displayed by default.
USNM PAL 530086_6
Steve Jabo
USNM PAL 530086_5
Steve Jabo
USNM PAL 530086_7
Steve Jabo
USNM PAL 530086_4
Steve Jabo
Allosaurus is represented here by selected fossil records from known especially from the morrison formation of the western united states, with additional reported jurassic records from portugal. Fossil Atlas maps those records as modern discovery locations.
No. The map shows modern fossil discovery locations from selected records. Ancient habitat and paleogeographic reconstructions are separate questions.
The current Fossil Atlas records include Morrison Formation. Formation coverage depends on the selected dataset and may not be complete.
Yes. Use the expedition card generator to turn the Allosaurus map and specimen profile into a shareable card.
Selected fossil records from PBDB and museum biodiversity aggregators. This is not a complete fossil count by country; source labels and confidence notes help distinguish canonical paleobiology records from specimen-media records.
Reconstruction images are labeled illustrations and do not represent fossil evidence. Size, speed, and bite-force figures are typical published estimates and remain subject to revision as new specimens are described.
Maps use curated PBDB, museum, and specimen-source records with visible caveats.
Pins show where fossils were found or reported today, not exact ancient habitat positions.
Artwork is labeled separately from specimen photos, maps, and source records.
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