Allosaurus fragilis
"The first big killer, the terror of the Jurassic: Allosaurus, the most advanced flesh-eater of its day. Now these are the lions of the Jurassic. The top predators of their age."

Allosaurus ("Different" or "Strange Lizard"), also known as "The Terror of the Jurassic", was a genus of large carnivorous theropod dinosaur (an allosaurid) that lived some [156 -145] during the Late Jurassic period. It was also the largest, most common, and most dangerous predator of the Late Jurassic period.



Allosaurus was the largest and top predator of the Late Jurassic Period, from 156-145 million years ago, ruling Western North America for 11 million years. It was the apex predator of its time, the King of the Jurassic. Allosaurus died out at the end of the Jurassic period, alongside with its contemporaries - Camarasaurus, Ceratosaurus, Stegosaurus, etc.


As the the largest Jurassic meat-eating dinosaur and the first giant predator dinosaur the ever walked North America, Allosaurus was one of the largest predatory dinosaurs that ever lived. Measuring on average between 30 to nearly 40 feet long, standing 13 to 16 feet tall, and weighing up to 3 to 5 tons, they were the size of a railroad box car. The largest allosaurus ever found stood about 16.5 feet tall, measured 45 feet in length, and weighed up to 6-7 tons, making it almost as large as Tyrannosaurus Rex.

Like most meat-eating dinosaurs, its jaws were filled with serrated teeth shaped like blades. Computer studies suggest that Allosaurus attacked by using its upper jaw like a battle axe to hack at its victim, then it used its lower jaw to bite out a slice of meat.

It might have been easy for an Allosaurus to kill a fairly defenseless dinosaur like Camptosaurus, but Stegosaurus could certainly put up a fight, and the sauropods (giant long-necks) were so huge that they could easily crush even an adult Allosaurus with a blow from their tail, or a stomp from their legs.


Like most predatory dinosaurs, Allosaurus hunted alone, in pairs or in packs of up to 3-4 individuals. Though probably not much smarter than a modern crocodile, it was still a literally bigger and better model than the earlier carnivores, such as Ceratosaurus, who died out under the pressure of the bigger Allosaurus.

Allosaurus led a dangerous life. The Allosaurus on display at the Smithsonian Institute has a smashed shoulder blade, many broken ribs, and a lower jaw so damaged that paleontologists didn't realize it was an Allosaurus jaw for over 100 years! But these were tough dinosaurs: Their bones show that they lived long enough for their wounds to heal.

Nevertheless, for its day, it was top of the line in a general context, and a deadly carnivore rivaled by few other Theropods on Earth in the Late Jurassic Period, outclassing the more primitive Ceratosaurs and Coelophysoideans. In short, the Allosaurus were plucky carnivores that probably endured just into the Early Cretaceous (the Berriasian Stage, it seems likely because a finger bone was found from this time). They were after all, the 'Lions of the Jurassic'.

Allosaurus gave its family their name, and the Allosaurs lasted for tens of millions of years, only being replaced in importance during the Cretaceous. Torvosaurus may have been a rival, one could speculate, as it was just as fearsome. Allosaurus was one of the most succesful predators of its day.


Allosaurus fossils have been found in Western North America in states such as Colorado, Utah, Wyoming, and Montana.