Allosaurus was death on two legs – two very strong, very powerful legs. With a length of 35-40 feet, a height of 16 feet and weighing in at 3 tons, Allosaurus was a ferocious carnivorous dinosaur that terrorized the earth during the Late Jurassic Period 150 million years ago. Until 50 million years later, when the tyrannosaurs emerged, Allosaurus was the largest predator in existence. The giant lizard was grouped with theropod dinosaurs, carnivorous beasts with small forelimbs that were propelled by strong hind legs. It resembled a downsized version of the fearsome Tyrannosaurus Rex. Allosaurus is generally ranked fifth among the most immense meat-eating dinosaurs.
Meaning "other reptile" – since its vertebrae differed from those of other dinosaurs – Allosaurus was equipped to mercilessly kill. It had steely neck muscles and a tough skull outfitted with massive jaws harboring 4-inch, back-curving teeth resembling serrated daggers. Because the teeth faced backwards, Allosaurus' victim would be forced farther down the dinosaur's throat with each struggle. Allosaurus, like numerous meat-eaters, frequently grew and shed its teeth, and generally had 16 teeth at any given time, so it left behind many fossilized fangs.
Its short front limbs belied their strength, and the three fingers on each hand were topped off with menacingly curved, razor-sharp claws that were over 6 inches long. Scientists have surmised that Allosaurus could move at speeds up to approximately 20 mph. If it traveled any faster, it would lose its balance, falling and crushing its arms under its body weight. However, because Allosaurus was so immense and violent, speed was moot.
Allosaurus was the primary foe of the giant sauropods, or plant-eaters, such as Apatosaurus (formerly Brontosaurus) and Diplodocus, even though these enormous creatures weighed 30 tons, compared to Allosaurus' 3 tons. What Allosaurus lacked in size, it made up for in sheer viciousness. To bring down such large quarry, it may have used its formidable upper jaw like a hatchet, knocking its prey sideways and then tearing away flesh with its teeth. It is speculated that the ferocious Allosaurus may have competed with the meat-eater Ceratosaurus for iguanodonts, stegosaurs and sauropods.
Any animal it could overpower or ambush was fair game for Allosaurus. The earth-shaking bulk of the sauropods may have, at times, been a hindrance for even the most sizeable Allosaurus. Becoming opportunistic in these situations, Allosaurus attacked old or weak animals, or stole carcasses that had been brought down by other animals. There is even evidence that it often clashed with the 20 foot-long, 2 ton Stegosaurus, an otherwise peaceful plant eater with an armor of bony plates on its back, and a formidable spiked tail or "thagomizer."
As an apex predator, Allosaurus faced little chance of having its life cut short. Baby Allosauruses ate insects, including dragonflies and centipedes, until age 2, when they started consuming small dinosaurs. Paleontologists estimate that Allosaurus was a full-sized adult by age 15, putting on 330 pounds per year. In lieu of starvation, disease or thagomizer injuries, it could have lived to be about 25 or 30 years old.
Allosaurus was a very common dinosaur to roam North America. At Utah's Cleveland-Lloyd Dinosaur Quarry, a vast number of its bones have been found. Since 1927, over 10,000 bones have been excavated, and approximately half are Allosaurus bones. The quantity of the predator's bones is unique, because there is usually one meat-eater for every 10 plant-eaters. It's been speculated that this was an area where prey animals were trapped, possibly by tar. Then the predators came to feed on them, and also became entrapped. None of the Allosaurus skeletons are intact – they were probably trampled and jostled in the ensuing panic.
The Allosaurs acquired from this quarry spanned all ages and sizes. Animals were discovered that were only a bit more than a foot long to over 40 feet long, with a weight of over 2 tons. Other Allosaurs topped out at 49 feet long and weighed 3 tons.
In 1991 – after an entire century of Allosaurus unearthings – researchers discovered a magnificently preserved, nearly complete fossil which they named Big Al, and which became the most famous Allosaurus fossil. Twenty-six feet long and still a teenager, Big Al was subject to numerous bone fractures and bacterial infections which, unfortunately, cut his life short. Later, the same team unearthed a comparable Allosaurus fossil which was even better preserved than Big Al, and which was dubbed Big Al 2.
Another area rich in Allosaurus fossils is North America's Morrison Formation, where the great beast's bones have been preserved for the last 150 million years. The Morrison Formation is comprised of ancient rock stretching all the way from Montana to New Mexico, that used to pass through a prehistoric world of rivers, lakes and plains, making it the ideal ecosystem for Allosaurus to thrive.
Even though Allosaurus is gone, its fearsome mystique of aggression, ferocity and sheer savagery live on. For years, it reigned at the top of the food chain. And that's a very good place to be.