An Ultimate Guide to Allosaurus: The Different Lizard

Leave a comment / / Updated on: 28th October 2023

Name Meaning“The different lizard”Height4-5 meters (13-16.4 feet)
PronunciationAl-oh-sore-usLength9.7 meters (32 feet)
EraMesozoicLate JurassicWeight1.7-2.7 metric tons (1.9-2.5 short tons)
ClassificationDinosauria,‭ Saurischia & TheropodaLocationPortugal, North America

Allosaurus Pictures

3D illustration of Allosaurus
3D illustration of Allosaurus | Warpaintcobra via iStock

The Allosaurus

Gage Beasley Prehistoric's Allosaurus Concept
Gage Beasley Prehistoric’s Allosaurus Concept

The Allosaurus, one of the most popular prehistoric creatures, lived in Portugal and North America roughly 155-145 million years ago. 

This makes it a common Late Jurassic dinosaur that lived among the many other prehistoric creatures in the Lourinha and Morrison Formations.

If you’re wondering what makes the Allosaurus so noteworthy, we encourage you to keep reading! 

We’ve prepared some fascinating details to help you understand this dinosaur better!

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Gage Beasley’s Prehistoric Shirt Collection
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Gage Beasley’s Prehistoric Plush Collection

Physical Characteristics

Gage Beasley Prehistoric's Allosaurus Concept
Gage Beasley Prehistoric’s Allosaurus Size Comparison Chart

The Allosaurus was a typical theropod featuring the following characteristics:

  • It had a massive skull and a short neck.
  • Each dentary had 14-17 teeth with saw-like edges, which became shorter and narrower toward the back of the skull. The Allosaurus shed these teeth regularly and was subsequently replaced, which is why tooth fossils are now very common.
  • It had a pair of horns consisting of lacrimal bone extensions and was likely covered in a keratin sheath.
  • It was bipedal and thus had short forelimbs, representing only 35% of the hindlimb length. Although small, the arms were strong.
  • Each hand had three fingers equipped with large, curved claws. 
  • The hindlimbs were smaller than those of tyrannosaurids. The toe claws were hoof-like. Three toes were weight-bearing, while the fourth was a dewclaw, meaning it didn’t make contact with the ground while the dinosaur was standing.
  • Its tail was long, slightly bent downward, and probably consisted of approximately 45-50 vertebrae.
Gage Beasley Allosaurus Unisex T-Shirt
Gage Beasley Allosaurus Unisex T-Shirt

The size of the Allosaurus has been the subject of numerous debates. 

Moreover, since more than one species are in the genus, it would be difficult to indicate an overall size for all. 

It has been suggested that the type species A. fragilisi measured, on average, 8.5 meters (28 feet) long and weighed 1.7 metric tons (1.9 short tons).

The maximum length was established at 9.7 meters (32 feet) long, and the weight at 2.3-2.7 metric tons (2.5-3 short tons). 

Others suggested a length of 12-13 meters (39-43 feet), while some argued that the more appropriate weight for the Allosaurus was 700 kilograms (1,500 pounds).

Supposedly, A. europaeus was smaller, measuring only 7 meters (23 feet) long and weighing one metric ton (1.1 short tons).

Habitat and Distribution

Allosaurus fossils were discovered in the Morrison Formation. More precisely, they were recovered from the following localities:

  • Middle Park, located near Granby, Colorado
  • Garden Park, located north of Cañon City, Colorado
  • Como Bluff, Wyoming
  • Cleveland-Lloyd Dinosaur Quarry, Emery County, Utah
  • Shell, Wyoming
  • District of Leiria, Portugal

In short, the fossils belonging to this genus were recovered from North America’s Morrison Formation and Portugal’s Lourinha Formation.

Studies show that these two formations were very similar in terms of habitat, flora, and fauna, and the fact that Allosaurus was found outside North America, precisely in Portugal’s Lourinha Formation, isn’t surprising, as many other dinosaurs were distributed this way, one of them being the Stegosaurus.

Both formations had a warm and wet climate, featuring seasonal variations in precipitation. 

A 3D image of a Allosaurus within a hot climate
A 3D image of a Allosaurus within a hot climate | Stocktrek Images via GettyImages

However, the Lourinha Formation was believed to have had a wetter climate as it was much closer to the recently opened North Atlantic. 

As such, the territory had around 766-1394 mm/year of precipitation in the north, even wetter in the south with 877-1360 mm/year.

The Morrison Formation is believed to have been a semiarid to tropical wet-dry habitat. 

It likely consisted of wet and dry seasons. 

Paleontological expeditions revealed the fossils of the following plants:

  • Green algae
  • Horsetails
  • Ferns
  • Conifers
  • Cycads
  • Ginkgoes
  • Mosses
  • Fungi 

Some scientists stated that the seaway between North America and Eurasia was too narrow to prevent plants from spreading, so the Lourinha Formation probably had the same flora. 

Behavior and Diet

Theropods such Allosaurus are know to be bipedal
Theropods such as Allosaurus are known to be bipedal | leonello via iStock

The Allosaurus was a bipedal predator that fed on large animals. 

Strong evidence suggests these creatures attacked and killed Stegosaurus individuals, but they probably weren’t the only prey the Allosaurus went for. 

They’re considered to have been both active predators and scavengers.

On the other hand, unless it hunted alongside other allosaurs, it probably preferred attacking smaller or juvenile prey, as the size of its skull and teeth didn’t give it the upper hand against much larger dinosaurs. 

Some studies show that, although the skull was strong, the bite force was relatively small, producing a maximum bite force of approximately 8,724 N.

As such, specialists argue that the Allosaurus likely attacked prey with its mouth open, slashing the flesh with its teeth but leaving the bones intact, as its bite force wasn’t strong enough to damage them.

These dinosaurs probably preyed upon ornithopods as well, attacking them in a way similar to modern big cats, meaning they grasped it with the forelimbs and delivered several bites on the throat.

Allosaurus killed its prey by attacking the neck area
Allosaurus killed its prey by attacking the neck area | MARK GARLICK via GettyImages

The Allosaurus is thought to have moved at a maximum speed of 30-55 kilometers per hour (19-34 miles per hour). 

It likely possessed binocular vision, but it was very limited. 

Still, it was enough to see prey and understand the distance between them.

Like other allosaurs, the members of the Allosaurus genus may have hunted in packs. 

However, some scientists suggest they were probably quite aggressive toward others of their kind, and cooperative hunting, if possible, was rare. 

Other scholars support the theory that they gathered together not to engage in cooperative hunting but to feed on the abundant dinosaurs in the area. 

A pair of Allosaurus attacking a much bigger prey
A pair of Allosaurus attacking a much bigger prey | Fred Wierum via Wikipedia CC BY-SA 4.0

Evidence shows that they might have even engaged in cannibalistic behavior!

Life Cycle

Like all dinosaurs, the Allosaurus reproduced by laying eggs, two at a time. 

An illustration of an Allosaurus egg
An illustration of an Allosaurus egg | Image via ARK: Survival Evolved Fandom

Compared to modern birds, which lay only one egg at a time because they have only one functional oviduct, female dinosaurs had two functional oviducts.

Paleontological discoveries revealed medullary bone tissue in at least one specimen. 

This medullary bone was rich in calcium and was grown only in females because it served as an aid in supplying the eggshells with calcium. 

The presence of this bone helped scientists establish the sex of the dinosaurs and indicate when juveniles became sexually mature. 

On the other hand, other studies disapprove of this theory and suggest that the bone should be linked merely with bone pathology.

The discovery of fossils belonging to a juvenile revealed that they had longer hindlimbs compared to adults, and the shin and foot were longer than the thigh. 

As such, juvenile Allosaurus individuals were probably faster than adults, thus having different hunting strategies. 

Restoration of a juvenile Allosaurus
Restoration of a juvenile Allosaurus | Fred Wierum via Wikipedia CC BY-SA 4.0

It has been suggested that, as juveniles, these dinosaurs chased small prey. 

They switched to an ambush technique and went for larger dinosaurs when they reached adulthood.

It is believed that Allosaurus individuals reached sexual maturity by age ten and stopped growing by age 15, adding approximately 148 kilograms (326 pounds) per year. 

The same study shows that these dinosaurs’ age limit was 22-28 years.

Evolution and History

Life restoration of A. fragilis
Life restoration of A. fragilis | Fred Wierum via Wikipedia CC BY-SA 4.0

The Allosaurus is part of the Allosauroidea superfamily. 

Paul Sereno was the first to define this superfamily, naming its members all neotetanurans closer to Allosaurus than to Neornithes (birds). 

Kevin Padian described this superfamily, stating that it consisted of the Allosaurus, the Sinraptor, and all the descendants of their most recent common ancestor. 

As such, Allosaurus fragilis is now the type species of the Allosauroidea superfamily.

Different species of Allosaurus
Different species of Allosaurus | Steveoc 86 et al. via Wikipedia CC BY-SA 2.5

The first described fossil belonging to this genus was discovered in 1869. 

It was a bone obtained in 1869 by Ferdinand Vandeveer Hayden and had been recovered from Middle Park. 

At first, locals thought that the bone was a petrified horse hoof. 

Who would’ve thought this petrified horse hoof would soon become one of the most important fossils in a superfamily of dinosaurs?

At first, this fossil was identified as being half of a tail vertebra. 

At the time, it was attributed to Poekilopleuron, a genus of European dinosaurs. 

Later, specialists coined a genus only for this newly discovered creature – Antrodemus.

The type specimen of the Allosaurus consists of a collection of fragmentary bones. 

Based on these remains, Othniel Charles Marsh named the species Allosaurus fragilisi

A. fragilis at the Cleveland-Lloyd Dinosaur Quarry museum
A. fragilis at the Cleveland-Lloyd Dinosaur Quarry museum | James St. John via Wikipedia CC BY 2.0

In 1920, Charles W. Gilmore suggested that the tail vertebra attributed to Antrodemus was identical to those attributed to Allosaurus, but he stated that the former name should be kept.

During multiple paleontological expeditions at the Cleveland-Lloyd Dinosaur Quarry, paleontologists discovered at least 46 Allosaurus fragilis specimens, alongside 30 other dinosaurs. 

These discoveries represented a major step in understanding this creature’s appearance and behavior.

The first Allosaurus fossils discovered in Portugal were reported in 1999. 

They were found in the Lourinha Formation and led to the naming of a new species, Allosaurus europaeus

At first, Allosaurus was proposed to consist of six species:

  • Allosaurus amplus
  • Allosaurus atrox
  • Allosaurus europaeus
  • Allosaurus fragilis
  • Allosaurus jimmadseni
  • Allosaurus Lucas.

In 2020, scientists argued that only A. fragilis, A. jimmadseni, and A. europaeus should be recognized. 

Diagram comparing skulls of the three recognized species of Allosaurus
Diagram comparing skulls of the three recognized species of Allosaurus | Daniel J. Chure et al. via Wikipedia CC BY 4.0

However, since the latter doesn’t possess unique characteristics, its validity is often questioned. 

Interactions with Other Species

The Morrison Formation, where Allosaurus was discovered, is one of the richest fossil localities in North America. 

Our different lizard was happy (or maybe not, who knows?) to coexist with so many other dinosaurs and prehistoric creatures! 

Most of them were theropods, like Ceratosaurus and Torvosaurus.

However, sauropods like Brachiosaurus and Diplodocus were also common, as were ornithischians like Stegosaurus. 

Allosaurus fossils are often associated with fossils belonging to Apatosaurus, Diplodocus, Camarasaurus, and Stegosaurus

The territory in Portugal likely had a similar fauna diversity.

The Allosaurus shared its habitat with other carnivores like the Torvosaurus and Ceratosaurus, so they had to coexist somehow and avoid competition for food, right? 

Dry season at the Mygatt-Moore Quarry
Dry season at the Mygatt-Moore Quarry | Brian Engh via Wikipedia CC BY 4.0

Some studies suggest that the other two carnivores were more active around water sources and in forest and underbrush terrains. 

The different lizard, on the other hand, was more compact and hunted in dry floodplains. 

This way, competition for food was limited.

Although Allosaurus was a carnivore, scientists do not rule out the possibility of it being preyed upon by other carnivores, possibly even by one of the two other theropods mentioned above.

Other prehistoric creatures thriving in the same ecosystem include:

  • Snails
  • Ray-finned Fishes
  • Crocodylomorphs
  • Mammals
  • Salamanders
  • Frogs
  • Turtles
  • Lizards
  • Sphenodonts

Cultural Significance

Big Al II" was discovered in the Morrison Formation from the famous Howe Ranch near Shell, Wyoming
This specimen known as “Big Al II” was discovered in the Morrison Formation from the famous Howe Ranch near Shell, Wyoming | The_Wookies via Wikipedia CC BY 2.5

Without a doubt, Allosaurus is one of the most well-studied dinosaurs of all time, thanks to the numerous fossils discovered over the years! 

Its appearance and behavior served as areas of interest for scientists worldwide. 

Thanks to their efforts in studying this prehistoric creature, dinosaur enthusiasts can discover more secrets of our world’s prehistory!

Naturally, media portrayals followed these discoveries, thus making the Allosaurus popular among people not working in the paleontological field! 

Jurassic Park fans may already be acquainted with this creature, as it has some notable appearances in the franchise. 

It also appeared in the Walking with Dinosaurs series, in several episodes of the Jurassic Fight Club, in Dinosaur Revolution, and in Planet Dinosaur.

Did you know that Allosaurus fragilis is also Utah’s state fossil?


Having been one of the most common carnivores in its habitat, the Allosaurus is now certainly among the world’s most popular dinosaurs!

This creature had short horns in front of its eyes, a light yet robust skull, and sharp teeth. 

It is known to have preyed on even large sauropods, although scientists suspect that pack hunting might have played an important role in subduing such large animals. 

Allosaurus was also thought to be quite aggressive, even toward those of the same species.


Was Allosaurus bigger than T-Rex?

The Allosaurus was similar to the T-Rex in terms of size. 

However, scientists state that the Allosaurus maximum length highly depends on each individual and the species. 

Some scientists indicate a maximum length of 9.7 meters (32 feet), while others are in favor of 12-13 meters (39-43 feet) long. 

The T-Rex measured 12.3-12.4 (40.4-40.7 feet) long.

Who would win: Allosaurus vs. Stegosaurus?

Allosaurus would probably win in a fight with Stegosaurus

In fact, it is known to have preyed upon this herbivorous ornithischian. 

Although the Stegosaurus might have been able to defend itself thanks to its armored body, this doesn’t guarantee a win.


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