‘Different Lizard’

The name Allosaurus came from the Greek language meaning “different lizard”. This was the name given at the time of its discovery due to the very unique features of its vertebrae which scientists at that time were fascinated by. Why? Well, Allosaurus’s vertebrae were concave on both sides and contained shallow cavities, which gave them a similar shape to that of an hourglass. These cavities and shape didn’t make the bones’ very strong, but made them much lighter.

Allosaurus lived on earth 155 to 145 million years ago during the late Jurassic period and the largest specimens may have been very similar in size to the Tyrannosaurus Rex.

Who discovered allosaurus?

The first Allosaurus was discovered in Colorado, North America in 1877 by palaeontologist Othniel Charles Marsh. There were only a few fragments of the dinosaur which caused quite a bit of confusion at first. Two years later a more complete skeleton was found but not fully examined until 1903 and it turned out to be one of the most complete theropod fossils ever found.

In 1991 a discovery of an Allosaurus resulted in the finding being named “Big Al”. Amazingly this at the time then became the best preserved Allosaurus to date. The fossil fascinated scientists as they were able to examine and conclude that the living Allosaurus sustained a great number of injuries and infections.

Scientists stated that “Big Al” was only 87% fully grown and the injuries, which included, toes, ribs, and vertebrae, healed poorly and may have indirectly lead to its early death. The fossil was so well preserved that scientists could tell it had developed infections from the trauma of its injuries.

Quick Allosaurus Facts

Name: Allosaurus
First Found: USA by Barnum Brown
When it lived: Late Jurassic period, 155 to 145 million years ago
Weight: Estimated 1 to 2 tons
Length & Height 12 to 13 meters (39 to 43 foot)
Diet: Carnivore

More sparse finds of a smaller species similar to Allosaurus and dating from the Early Cretaceous of North America and Australia, indicate that this versatile hunter might have survived the mass extinction at the end of the Jurassic period.

Allosaurus is the most common theropod in the vast tract of dinosaur-bearing rock in the American Southwest known as the Morrison Formation. Remains have been recovered in Montana, Wyoming, South Dakota, Colorado, Oklahoma, New Mexico and Utah, in the United States. There have also been finds in Portugal. Allosaurus shared the Jurassic landscape with several other theropods, including Ceratosaurus and the massive Torvosaurus.

what did allosaurus eat?

Allosaurus was an active predator of other large dinosaurs and a pure carnivore. There have been some dinosaur fossils of sauropods, stegosaurs, and ornithopods, which shows evidence of Allosaurus bite marks. There is evidence in Stegosaurus fossil’s that shows they were bitten by an Allosaurus, and there are Allosaurus fossils showing puncture wounds from a Stegosaurus tail. This proved they hunted other dinosaurs. Furthermore scientists believed they hunted in packs to take down larger prey, as a single Allosaurus wouldn’t have been able to take down a large dinosaur such as a Diplodocus.

Like the Tyrannosaurus Rex, the Allosaurus was likely to be a scavenger as well as a predator. They will simply chose the best route to get the maximum amount of meat and protein, and if that means feeding off a dead dinosaur then that is an easy way to get a full meal.

How big was allosaurus?

Allosaurus was a large theropod dinosaur, it was as tall as a giraffe in fact, and was also one of the most lethal predators that roamed the earth at the time.

Allosaurus was a large predator, and the largest fossil found, named “Big Al”, was 12 to 13 meters (39 to 43 feet) in length and weighed 1,500 kilograms (3,300 pounds). Using the theory that Big Al was only 87% fully developed, researchers have stated the range of an Allosaurus’s weight could have been between 3100 – 4400 Ibs (1400 kg – 2000 kg).

Allosaurus was a typical large theropod, having a massive skull on a short neck, a long tail and reduced forelimbs. This dinosaurs most distinctive feature was a pair of blunt horns, just above and in front of the eyes. Although short in comparison to the hindlimbs, the forelimbs were massive and bore large, eagle-like claws. The skull showed evidence of being composed of separate modules, which could be moved in relation to one another, allowing large pieces of meat to be swallowed. The skeleton of Allosaurus, like other theropods, displayed bird-like features, such as a furcula (wishbone) and neck vertebrae hollowed by air sacs.

Allosaurus size

Steveoc 86 Marmelad Scott Hartman, [4], Henrique Paes [5]., CC BY-SA 2.5, via Wikimedia Commons

‘short neck, massive body’

Allosaurus had a short neck, a massive body, and powerful arms and claws. The forearm was shorter than the upper arm and each claw was strong and sharp enough to tear open the soft underbelly of any other Dinosaur. Allosaurus had a claw on each of the three fingers of both hands and used these claws to attack and hold onto its prey with devastating effect.

Their bodies were balanced by a muscular and long tail with estimations of the amount of vertebrae in the tail is between 45 and 50 and the tail was useful for lashing out at rival males during mating season when males fought for the attentions of females.

Allosaurus skeleton

Artwork by Scott Hartman, published by Daniel J. Chure, Mark A. Loewen, CC BY 4.0, via Wikimedia Commons

‘teeth as sharp as a steak knife’

The Allosaurus skull was of modest proportion compared to other theropods of its size. Their jaws had 14 to 17 teeth on both top and bottom which were each as sharp as a steak knife. The teeth were shed easily during feeding and were continually replaced.

Scientists have stated they used their skulls similar to swinging a sword. With an open mouth, swinging violently and from side to side to make sure its teeth were causing maximum damage to its prey. The thought behind this was because Allosaurus had a bite that was weaker than modern day predators such as lions and crocodiles, so it needed to attach and kill its prey differently.

Its vision was thought to be better than other dinosaurs as its eyes were in front of its head meaning it was likely to be good at working out distance and time. Good vision was counterbalanced with poor hearing, Allosaurus had crocodile like ears and only able to hear low frequency sounds.

Allosaurus’s sense of smell was well developed which allowed it to be able to smell its prey from a distance.

allosaurus habitat

Allosaurus’s have been found discovered in the famously rich Jurassic fossil area of the Morrison Formation which is in the Western area of the United States. Fossils have been found in US states Colorado, Montana, New Mexico, Oklahoma, and South Dakota, as well as in another country Portugal.

Allosaurus shared the landscape with several genera of giant sauropods such as Apatosaurus, Diplodocus and Camarasaurus as well as other herbivores such as Stegosaurus and Camptosaurus, all of which may have been potential prey to the Allosaurus.


Allosaurus’S legs were not suited for speed when compared to other dinosaurs such as the T- Rex, but still the estimated top speed of the Allosaurus is 30 to 55 km per hour (19 to 34 miles per hour). It is also believed that Allosaurus may have been able to swim if needed too.


Fossilised droppings have been found and were 1.52 meters (5 feet) in length and 10.2cm (4 inches thick). That is an enormous amount of dung.

Baby or young Allosaurus

Fred Wierum, CC BY-SA 4.0, via Wikimedia Commons

Similar dinosaurs to allosaurus

Tyrannosaurus Rex

Although Allosaurus was not an ancestor of the Tyrannosaurus Rex, and they were on earth at different times (T-Rex was on the earth 90 million years later), they have often been talked about in the same conversations due to their pure predatory nature, and physical similarities.

T-Rex was first discovered in 1902 by American Palaeontologist, Henry Fairfield Osborn, when a huge skeleton was uncovered in Montana. Tyrannosaurus Rex could grow up to 43 feet in length and up to 20 feet tall. It weighed between 5.5 and 9 tons. That’s basically the equivalent to the height of the tallest giraffe, and weighs as much as a big African elephant.

Tyrannosaurus Rex was a pure carnivore, and like Allosaurus, was an active predator and scavenger. T-Rex grew incredibly quickly and went through hundreds of pounds of meat and carcasses at a time to fuel this growth.

The T Rex had tiny arms which measured only 1m or 3.3 ft long and it has been hypothesized that it used these for slashing its prey by using its claws to cause harm to its prey. Having short arms may have been beneficial as long arms could be broken and susceptible to disease. Others believe that the arms were an evolutionary left over which served for no predatory purposes.

Tyrannosaurus rex

DataBase Center for Life Science (DBCLS), CC BY 4.0, via Wikimedia Commons


Velociraptor was a very strange looking Dinosaur. Almost like a large ‘bird of prey’ but completely flightless. It had plenty of feathers,  which ran all the way down its tail. Velociraptor didn’t have a beak however, just a short and powerful jaw packed full of razor-sharp teeth. 

Velociraptor was a small theropod and carnivorous dinosaur. It is also thought that it would have hunted larger prey in packs.

On August 11th 1923, Peter Kaisen discovered the first Velociraptor fossil known to science. Velociraptor was the first dromaeosaurid to be discovered and is still the most well-known to scientists and palaeontologists, due to several incredibly detailed skeletons being found and studied extensively since its discovery. 

Velociraptor with feathers

Fred Wierum, CC BY-SA 4.0, via Wikimedia Commons

Summary of Allosaurus

  • Allosaurus was a pure carnivore predator
  • The very first Allosaurus fossils were discovered in 1877 by American Palaeontologist, Othniel Charles Marsh.
  • Allosaurus fossils have been found in North America, Portugal
  • Allosaurus lived 155 to 145 million years ago in the late Jurassic period. 
  • Allosaurus was estimated to measure up to 12 to 13 meters (39 to 43 feet) in length Diplodocus weighed up to 1,500 kilograms (3,300 pounds).
  • Allosaurus was a theropod dinosaur

Last Updated on 15/07/2022 by