Allosaurus was as tall as a giraffe, but unlike this gentle herbivore, it was a lethal killer that may have hunted its prey in packs.
The most well-known of the late Jurassic theropods, Allosaurus was unearthed by Othniel Charles Marsh during the ‘bone wars’, and since then many specimens have been found. The Cleveland-Lloyd quarry alone has yielded more than 44 individuals. Species attributed to Allosaurus have been found as far away as Tanzania and Portugal. Sauropod bones have been found bearing marks gouged by Allosaurus teeth.
It was a theropod and it could grow up to 12m long. Although it was not as large as the largest carnivorous dinosaur Tyrannosaurus, it was just as vicious. Allosaurus was armed with enormous jaws, full of sharp, jagged teeth. It also had curved claws and a powerful tail to lash out at any animal brave enough to attack it.
Name: Allosaurus, meaning ‘different lizard’
Size: about 12m long
Food: meat, especially other dinosaurs
Lived: about 150 million years ago in the Late Jurassic in North America, and possibly Portugal and Tanzania
Allosaurus is a familiar animal, with its massive hind legs, its strong S-shaped neck, its huge head with jaws that could bulge sideways to bolt down great chunks of meat; sharp, serrated, steak-knife teeth with 5cm-long crowns, and its short, heavy arms with three-fingered hands bearing ripping claws that were up to 15cm long. This enormous carnivore would have hunted the biggest herbivores of the time, including the massive sauropods, the remains of which were found in the Cleveland-Lloyd quarry.
If a tall man could have stood on another’s shoulders when Allosaurus was alive, he would have been at just the right height to peer into its mouth. He would have seen rows of about 70 saw-edged teeth. All its teeth curved backwards, perfect for biting the flesh of its prey and preventing it from escaping. If any of its teeth fell out or were wrenched out in a fight, each was replaced by a new one that quickly grew to fill in the gap.
Scientists think that Allosaurus moved at about 8km/h. A jogger could have just about kept up with it as it strode along on its back legs like an enormous bird. Experts can also tell from fossil footprints that each step Allosaurus took was as long as a car.
The four toes on both feet ended in sharp, bird-like claws. Three of them pointed forwards and one backwards. Each claw was strong and sharp enough to tear open the soft underside of any other dinosaur. Allosaurus also had a claw on each of the three fingers of both hands. It used them to attack and hold onto prey.
Allosaurus probably held up its long, powerful tail when walking or running, to balance the weight of its body. Its tail had about 50 bones in it and was useful for lashing out at a rival during the mating season – when male fought male for the attentions of a female. Small, carnivorous dinosaurs which attacked Allosaurus’ young were probably seen off one mighty sweep of the tail.
Allosaurus was so large that it must have needed a considerable amount of meat to fill its ever-hungry stomach. It preyed on the herbivorous dinosaurs that lived in the same area.
Allosaurus’ toothmarks have been found on the tail bones of Apatosaurus, a North American herbivore. Some of the really huge herbivores, such as Diplodocus, were far too large for Allosaurus to attack on its own, so Allosaurus may have grouped together and hunted in packs.
Several members of the Allosaurus pack charged in to attack, biting and clawing at defenceless Diplodocus until it slumped to the ground to be ripped apart by the rest of the pack. Allosaurus would have had no hesitation in attacking the young of these large dinosaurs.
Catching fresh meat was a hit and miss business, so Allosaurus probably also fed on the leftovers of animals killed by other carnivores. This is called scavenging.
Allosaurus fossils have been found at sites in Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah and Wyoming, USA.