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Visit the museum to meet our young Allosaurus. He’s quite friendly, usually. He hasn’t even a visitor in weeks.

Fast Facts

NAME: Allosaurs fragilis

Meaning: Allosaurus means “different lizard,” named for its unusual vertebrae that have hollow places in some of them. This was different than other dinosaurs known at the time. The hollows may have held air sacs like similar spaces in the bones like modern birds. “fragilis” means fragile, or easily broken.

Pronounced: AL-oh-SAWR-us

Named by: Othniel Charles Marsh, in 1877.

DIET: Carnivore (meat eater) it ate plant eating dinosaurs, like stegosaurus and iguanodonts

SIZE:      Length: about 40 ft (12 m) long

Height: 10 ft (2 m) tall at the hips

Weight: up to 4.5 tons (9,000 lbs)

WHEN IT LIVED: Late Jurassic Period, about 155-145 million years ago

WHERE IT LIVED: North America and Europe. Fossils have been found in Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah, and Wyoming. Arizona has few rocks of the right age but there is little doubt it lived here too. Allosaurus fossils have also been found in Portugal, Europe, and perhaps Tanzania, Africa, and Australia.


 Family Allosauridae

  Genus Allosaurus

   Species: Five species are known, plus one type that has not yet been formally described.

  All the North American species may have been found in Arizona.

  1. A. fragilis Marsh 1877, from North America. The most common species.
  2. A. atrox Marsh 1878, from North America.
  3. A. amplus Marsh 1879, from North America.
  4. A. lucasi Dalman 2014, from North America.
  5. A. europaeus Mateus et al. 2006, from Portugal
  6. “A. jimmadseni”, from Portugal (not yet formally named)

Quick Facts:

Allosaurus was the most common top predator of its time. It had a huge head, and a mouth that opened extremely widely to expose its sharp, serrated teeth. Its short arms were powerful and built for grasping, it could even hold prey against its body.


Some dinosaurs related to Allosaurus are known to have had feathers, and some have speculated that Tyrannosaurus did too. Most paleontologists now seem to agree that they probably had feathers as young, but adults would have had few if any. They may very well have had a feathery crest running along their back, and perhaps more.

 Allosaurus fragilis portrait show it’s wide gape.

Art by Bob Hole

Allosaurus fragilis: A Predatory Titan of the Jurassic


Allosaurus fragilis is one of the most well-known and awe-inspiring dinosaurs from the Late Jurassic period. This magnificent theropod dinosaur roamed the Earth approximately 150 million years ago, and its fossils have captivated paleontologists and biologists for over a century.

Discovery and Taxonomy

Allosaurus fragilis was first described by the American paleontologist Othniel Charles Marsh in 1877. The name “Allosaurus” is derived from Greek, meaning “different lizard,” while “fragilis” refers to the delicate nature of its fossils. Several species of Allosaurus have been named, but Allosaurus fragilis is the most widely recognized and studied among them.

The first fossil specimens were unearthed in the Morrison Formation, a geological unit in western North America, primarily found in present-day Utah, Colorado, Wyoming, and Montana.

Fossil evidence of Allosaurus includes skeletal remains, teeth, and trackways, providing researchers with valuable information about its physical attributes and behavior.

Anatomy and Morphology

Allosaurus fragilis was a formidable predator, belonging to the theropod group of dinosaurs. It was a large bipedal carnivore, possessing a unique combination of physical features that made it a successful hunter. The dinosaur measured approximately 30 feet in length, although some individuals might have grown even larger. Its massive head was equipped with strong jaws lined with serrated teeth, which allowed it to effectively tear into its prey.

One of Allosaurus‘ most distinctive features was its three-fingered hands with sharp claws, which were undoubtedly instrumental in capturing and dispatching its victims. Its long, muscular tail acted as a counterbalance during locomotion, providing stability and agility while pursuing prey or engaging in territorial disputes.

Behavior and Ecology

As a top predator of its time, Allosaurus fragilis likely played a crucial role in shaping the Late Jurassic ecosystems in which it lived. Its predatory behavior suggests that it was an active hunter capable of taking down various types of other dinosaurs that shared its habitat, including sauropods like Brachiosaurus and Diplodocus.

Based on fossil evidence, paleontologists believe that Allosaurus might have exhibited both solitary and social behaviors. Solitary individuals could have been responsible for ambushing smaller prey, while larger social groups might have cooperated to take down larger herbivores. Trackways and bonebeds provide valuable insights into possible herding and social structures within this dinosaur species.

Feeding Habits

The sharp, serrated teeth of Allosaurus were highly adapted for slicing through flesh and tearing into the bodies of its prey. Analysis of its teeth indicates that it was well-suited for both inflicting puncture wounds and causing extensive damage to the tissues of its victims. This ability made Allosaurus an efficient predator, able to bring down relatively large and powerful dinosaurs.

Its feeding habits likely included scavenging, like most predators, allowing it to take advantage of the carcasses left behind by other predators or animals that died due to natural causes. This scavenging behavior would have provided an additional food source to support the energy demands of such a large and active predator.

Allosaurus and Other Dinosaurs

The Morrison Formation, where Allosaurus fragilis fossils are predominantly found, is famous for its diverse dinosaur fauna. Alongside Allosaurus, other Jurassic dinosaurs such as Stegosaurus, Apatosaurus, and Ceratosaurus inhabited the same region. Understanding the interactions between these different species provides valuable insights into the paleoecology and food webs of the ancient ecosystems.

Paleontologists have found evidence of Allosaurus interacting with other dinosaurs. Fossilized footprints reveal instances of Allosaurus trackways intersecting with those of herbivorous dinosaurs, indicating possible predator-prey interactions. Additionally, there is evidence of bite marks on herbivore bones that suggest predation or scavenging.

Extinction and Legacy

Despite its impressive adaptations, Allosaurus fragilis eventually succumbed to the mass extinction event that marked the end of the Jurassic period. The exact reasons for its decline and extinction remain a subject of ongoing research and debate among paleontologists.

Allosaurus‘ legacy lives on through the extensive research and popular culture references it has inspired. Its prominence in books, films, and documentaries has captured the imagination of people worldwide, further highlighting the allure of these ancient giants and the richness of our planet’s prehistoric past.


Allosaurus fragilis remains an iconic figure of the Late Jurassic, a time when colossal dinosaurs dominated the landscapes. As a powerful and intelligent predator, it played a pivotal role in shaping the ecosystems of its time. Its discovery and subsequent study have allowed us to gain a deeper understanding of the ancient world, providing valuable insights into the biology, behavior, and ecology of this remarkable dinosaur.

Through continued research and exploration, we hope to unravel even more secrets about Allosaurus fragilis and the ecosystem it inhabited.