Allosaurus, a prominent predator of the Jurassic Period, roamed the Earth approximately 155 to 145 million years ago. Its name, meaning “different lizard,” refers to its unique vertebrae, distinguishing it from other known dinosaurs. As a well-understood large carnivorous dinosaur, Allosaurus provides a clear example of a formidable ancient hunter. Its physical characteristics offer insights into its predatory lifestyle and how it interacted with its environment.
Overall Build and Stature
Allosaurus had a robust body, standing on powerful hind legs. An average adult Allosaurus fragilis reached about 8.5 meters (28 feet) in length. Some larger specimens suggest individuals could grow up to 9.7 meters (32 feet) long. Estimates for its weight vary, but a large adult A. fragilis likely weighed around 1.5 metric tons (3,300 pounds). This substantial build indicates a powerful and agile animal.
The Distinctive Head
The skull of Allosaurus was large, elongated, and lightened by numerous internal openings. Its jaws held dozens of sharp, serrated teeth, designed for slicing through flesh. These teeth were continually shed and replaced throughout the animal’s life.
A pair of bony crests or “horns” sat above and in front of each eye. Low ridges also ran along its nasal bones, connecting to these crests. While their precise function is debated, these crests were likely used for display. The eyes were large and forward-facing, providing good binocular vision, a useful trait for a predator.
Powerful Limbs and Tail
Allosaurus had short, muscular forelimbs, significantly smaller than its hindlimbs. Each hand possessed three fingers, tipped with large, curved claws suited for grasping and holding struggling prey.
The hindlimbs were long and powerful, built for swift movement and supporting its massive body. Each foot had three toes, along with a smaller, raised dewclaw. The long, heavy, and muscular tail provided a counterbalance to the front of its body. This tail enabled Allosaurus to maintain stability during movement and rapid turns.
Visualizing the Living Animal
Paleontologists reconstruct Allosaurus’s appearance from its skeletal remains, inferring muscle attachment points and body shape. Its robust bones indicate a muscular physique, particularly in the legs and neck, supporting its predatory capabilities.
While the skeletal structure provides a strong foundation, features like skin texture and coloration are more speculative, relying on comparisons with modern reptiles and birds. Rare skin impressions offer clues about scale patterns, indicating a scaly or pebbly texture. Coloration is often inferred based on principles like countershading, where a darker back and lighter belly could provide camouflage. These reconstructions combine scientific evidence and informed speculation to create an image of the Allosaurus.