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Allosaurus fragilis Dinosaur Facts

Allosaurus fragilis is one of the first dinosaurs to appear on the big screen during his cameo appearance in the silent feature film "The Lost World", produced in 1925. This film adaptation of the novel of the same name by Sir. Arthur Conan Doyle also featured the Pteranodon pterosaur and the Apatosaurus sauropod. Although convincing in its role of villain, the celebrity of Allosaurus in Hollywood was only short-lived since it was replaced a few years later in blockbuster King Kong by an even more terrifying creature, the T-Rex.

The Lost World and King Kong

Allosaurus vs Tyrannosaurus

These creatures are both ferocious and fearsome carnivorous theropod giants who occupied the top of the ecological niche in their respective times. Allosaurus dominated the midwestern landscapes of the Upper Jurassic while the Tyrannosaurus terrorized the Laramidia forests in South Dakota during the Late Cretaceous era. Although these apex predators are similar in many ways - they were large bipedal theropods with small hands and strong legs and torso - there are, however, several anatomical differences between the two. The T-Rex was only a few meters taller than Allosaurus (about 5 meters in larger specimens) but was much heavier. While Allosaurus weighed only 2 or 3 tons, the Tyrannosaurus could easily reach a weight of more than 10 tons. This lighter silhouette gave this dinosaur mobility and increased movement speed. Another noticeable difference between these two monsters is that Allosaurus had longer arms; his hands were also bigger and had three fingers rather than two.

The jaw of the Tyrannosaurus is well known to be extremely powerful, literally grinding and smashing bones by applying a compression force comparable to the weight of an elephant. That of Allosaurus, by comparison, is surprisingly weak. Estimates based on scientific models have shown that the bite force of the latter is less than that of lions, alligators and leopards. The hunting methods used by the animals should therefore differ slightly.

The T-Rex wins all the popularity contests since it is so widely known because of its recent film roles that it is virtually impossible for other dinosaurs to compete. It is so popular that most people know its scientific name as well as its abbreviations. However, this does not detract from Allosaurus which is greatly appreciated by dino lovers and enjoys a celebrity comparable to that of Dilophosaurus.

Allosaurus had two little horns in front of his eyes

Allosaurus skull

Allosaurus can easily be distinguished from other large carnivorous theropods since this carnosaur possessed two small horns in front of the eyes which were extensions of the lacrimal bones of the skull and which are strangely reminiscent of the double ridges of the Dilophosaurs. His head was disproportionate to the rest of his body and his neck was short and strong. He also had small streaks that spread from the top of his nasal bones to his horns.

Allosaurus teeth

Allosaurus teeth

Like many other predatory dinosaurs of the Mesozoic era, Allosaurus' teeth grew and fell rapidly and had to be constantly replaced. Each fang was 3 to 4 inches long, much shorter than the Tyrannosaurus whose teeth were the size of a big banana. Curiously, the mouth of this dinosaur had the same number of teeth as those of humans, 32, distributed equally between the upper and lower jaw. Because the fossils of Allosaurus are very common, anyone willing to shell out a few hundred dollars can acquire an authentic tooth. Who would not like to be able to boast of owning a dinosaur tooth?

Origin of the name

Allosaurus vertebrae

The name Allosaurus means "different lizard". It has been named because its vertebrae are different from any other dinosaur species known at the time. These have a concave shape on each side creating small cavities that make them look like an hourglass. This feature made the bones lighter but also weaker and brittle. We also find these small empty spaces in modern birds and it is believed that they were used to contain small bags of air for breathing.

Allosaurus diet

We know beyond any doubt that this dinosaur was a carnivorous hunter. Its prey of choice were large herbivorous dinosaurs such as sauropods (Brachiosaurus, Diplodocus), ornithopods and possibly Stegosaurus. Paleontologists have unearthed strong evidence that Allosaurus at least engaged in vigorous fights with stegosaurs. Puncture wounds (the same type of wounds inflicted by pointed weapons) have been found on the vertebrae of a specimen whose size and shape correspond perfectly to the stegosaur's tail tip (thagomizer). In addition, Allosaurus bite marks were also found on the cervical bones of stegosaurs.

Allosaurus possibly hunted in packs

It has long been speculated that the only way this dinosaur could overcome huge sauropods of 50 tons was to hunt in packs. There is however no scientific evidence that supports this theory. It is more likely that it was lurking in the undergrowth while waiting for a carefree herbivore to pass by. Like a lion quietly stalking his victim in the savannah, Allosaurus waited for the perfect opportunity before going out of his hiding place and rushing towards his meal. It almost certainly had to catch the stragglers in the large nomadic herds of herbivores: the young, the old, the wounded and the sick. It is inconceivable that an animal of barely three tons could attack a healthy one of several tens of tons directly.

Allosaurus used his jaw like a hatchet

Since the pressure of his jaw was relatively small (350 pounds per square inch) compared to other predators, Allosaurus had to have another way to kill his prey. His mouth could open very large and expand. This fact combined with his powerful neck muscles lead some people to speculate that it was using his mouth as a hatchet. It leaped on his victim, grabbing it with more developed hands and claws, and stabbing the unfortunate on the trachea with his upper jaw in a vertical up and down motion. His prey, in a severe state of shock, fainted and died shortly afterwards at the end of his blood. This is a very effective way to kill and probably one of the reasons why Allosaurus was such an energetic hunter. The element of surprise also played a decisive role in the success of the attack when it attacked larger animals.

The element of surprise

Occasionally scavenger

On the rare occasions when it could not feed himself by hunting, Allosaurus was a scavenger. It ate the little protein available on the carcasses it came across on his way. Although this was not enough to quell hunger, it was a sufficient source of energy until the hunt came to fruition.

Interesting Allosaurus facts

There is still debate as to whether Allosaurus is actually the same dinosaur as Saurophaganax, another two-ton theropod that lived in North America during the Upper Jurassic. Since physical resemblances are striking and fossil evidence is scarce, one can only speculate.

Another interesting fact, since it is one of the first fossils to be found, it is also the instigator of the "War of fossils - Bone wars" which opposes two of the greatest paleontologists in history: Othniel C. Marsh and Edward Drinker Cope. In a wave of rivalry, the latter frequently "diagnose" new species based on meager amounts of bones that turned out to be different kinds of Allosaurus.

In addition, as is common when you discover a new species of dinosaur, Allosaurus found itself in many bins of rankings. The American paleontologist Joseph Leidy originally gave it the name of Antrodemus and it was not until the 1970s that we began to refer to this dinosaur under the name of Allosaurus.

Allosaurus Fossils

Skeleton fossil of Allosaurus

Allosaurus was one of the most common carnivorous dinosaurs of the Morrison Formation and therefore fossils are very abundant and for this reason one can retrieve information in large quantities on this beast. To date, researchers have unearthed more than a hundred remains of this dinosaur. It is considered the quintessential carnivorous predator of the Jurassic and is the fossil representative of the state of Utah. It is found in Colorado and Utah, and mainly in the Cleveland-Lloyd dinosaur quarry and at the Dinosaur Monument.

Big Al

Allosaurus fossil - Big Al
Big Al

The earliest remains date as far back as 1869 but the best-preserved fossil, nicknamed "Big Al", was discovered in the 90s and is shown at the University of Wyoming. This skeleton is nearly 12 meters long and scientists believe he was still immature at the time of his death. "Big Al" does not seem to have had a rosy life since skeletal tests revealed numerous fractures and bacterial infections that sentenced this teenager to an untimely painful death.

Big Al 2

Allosaurus fossil - Big Al 2
Big Al 2

Five years later, paleontologists have unearthed in the same vicinity a second fossil even better preserved than "Big Al", "Big Al 2, Resurrection". This fossil is also known to have suffered multiple injuries during its short existence; suffice to say that life as a predator during the Jurassic era was no piece of cake.

The Utah Museum of Natural History houses the world's largest collection of Allosaurus fossils. The age range is as follows: from babies up to three feet tall to larger adult specimens up to 35 feet long. The abundance of bones allows researchers to study the evolution of dinosaur morphology over time and old age.

Allosaurus species

In the history of this dinosaur, new species of theropods have often been named to realize after the fact that it was actually an Allosaurus. To date, there are three officially recognized species:

  • A. fragilis
  • A. europaeus
  • A. lucasi


People often wrongly believe that Allosaurus is a Tyrannosaurus since it looks a lot like the T-Rex. In fact, this dinosaur is a carnosaur and belongs to the family of allosaurids.

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