Allosaurus

Allosaurus was a large meat-eating dinosaur that lived in what is now North America. It walked the Earth during the late Jurassic period, about 155 to 145 million years ago. That means Allosaurus lived tens of millions of years before Tyrannosaurus rex. The two dinosaurs never met each other. Allosaurus was already extinct long before T. rex appeared.

An adult Allosaurus stood about 15 feet tall and stretched up to 32 feet from nose to tail. It weighed about two tons, close to the weight of a small car. Allosaurus walked on two strong back legs and held its body level with the ground, balanced by a long tail. Its arms were short but powerful, with three curved claws on each hand. Each claw could grow as long as a banana.

The skull tells the story of how Allosaurus hunted. Its jaws held about 70 sharp, saw-edged teeth. If a tooth broke off, a new one grew in to replace it. Allosaurus had two small bony bumps above its eyes, almost like horns. These probably helped it show off to other Allosauruses, a bit like antlers on a deer. Scientists studying its skull have found that Allosaurus did not bite down with huge force. Instead, it may have swung its open mouth like a hatchet, slashing at prey with its upper teeth.

Allosaurus hunted plant-eating dinosaurs of its time. One of its main targets was Stegosaurus, the spiky, plate-backed dinosaur. Fossils show that these two sometimes fought back. One Allosaurus skeleton has a hole in its tail bone that matches the exact size of a Stegosaurus tail spike.

Did Allosaurus hunt alone or in packs? This is still debated. Some scientists think groups of Allosauruses teamed up to bring down huge long-necked dinosaurs like Apatosaurus. Others argue that Allosaurus was not smart or social enough to hunt as a team, and that fossil groups were just hungry animals gathering at the same dead body. The question has not been settled.

Most of what we know about Allosaurus comes from a place in Utah called the Cleveland-Lloyd Dinosaur Quarry. More than 40 Allosaurus skeletons have been dug out of the ground there. Nobody knows for sure why so many died in one spot. Some scientists think a swamp or mud pit trapped them one by one over many years, each one lured in by the last one stuck inside.

Allosaurus is the state fossil of Utah.