Allosaurus

Allosaurus was a large meat-eating dinosaur that lived in prehistoric North America.

It had three-fingered hands and distinctive horns above its eyes.

Saurophaganax, a related dinosaur, was once thought to be a larger cousin of Allosaurus. But recent research has shown that Saurophaganax was probably named by mistake, and many of the bones actually belonged to Allosaurus.

Multiple Allosaurus specimens have been discovered together in the same bone beds, causing some researchers to wonder if Allosaurus may have hunted in packs.

However, there may be other reasons for the grouped fossils. Some Allosaurus remains have been found with possible evidence of bite marks from other Allosaurus, suggesting they may have attacked one another.

Nobody can say for sure whether individual Allosaurus cooperated with one another, but it’s likely they sometimes competed and fought.

While Allosaurus and Tyrannosaurus looked similar – both were large, two-legged carnivores – they weren’t closely related.

Allosaurus lived during the Late Jurassic Period, around 145 million years ago, whereas Tyrannosaurus lived many millions of years later during the Late Cretaceous – around 66 million years ago.

But both would have been top of the food chain during their respective time periods.

No one knows for sure why Allosaurus had small horns on its skull. There are several possibilities.

The horns might have been used for species recognition – in other words, to help Allosaurus recognise other Allosaurus. It’s also possible male and female Allosaurus may have had differently sized or coloured horns, perhaps as a mating display.

Some experts think the horns might have helped protect their eyes from sunlight. Some modern animals, such as eagles, have ridges above their eyes for this reason.

It’s also possible the horns played a role in protecting the skull during fights with other Allosaurus if they took part in headbutting or snout-pushing contests. But the horns probably weren’t strong enough to withstand direct, full-power combat.

Since the 1930s, scientists had thought that a collection of fossils from Oklahoma, USA, belonged to a larger relative of Allosaurus that eventually came to be called Saurophaganax.

However, some experts weren’t convinced. Some of the bones looked like they could belong to Allosaurus – and some of them might not even belong a meat-eating dinosaur at all.

Recently it was decided that some of the bones should be renamed to belong to a new species of Allosaurus – Allosaurus anax.

The rest of the remains are too fragmentary to say for sure what they belong to. They might even be from a plant-eating sauropod dinosaur, such as Diplodocus.

Allosaurus hunted many of the plant-eating dinosaurs that shared its environment in the Late Jurassic Period.

Researchers have found Stegosaurus fossils showing Allosaurus bite marks, and there’s also evidence of Allosaurus scavenging large sauropod remains. Experts aren’t sure if Allosaurus would have attacked very large herbivorous dinosaurs while they were alive or mostly fed on them after they were already dead.

It’s possible Allosaurus was a flesh grazer – meaning it may have bitten meat from large dinosaurs without killing them, allowing the prey dinosaur to survive and heal.