Allosaurus, a bipedal predator, roamed the Earth during the Late Jurassic period, approximately 155 to 145 million years ago. This dinosaur, whose name translates to “different lizard,” was a top predator of its time. This article explores the physical dimensions of Allosaurus and how its size influenced its existence.
Allosaurus Dimensions
Allosaurus was a large theropod, with an average length for A. fragilis, the best-known species, estimated at 8.5 meters (28 ft) from snout to tail tip. Some definitive specimens reached about 9.7 meters (32 ft) in length, while fragmentary remains suggest some individuals might have grown up to 12 to 13 meters (39 to 43 ft) long. Its standing height at the hip was typically around 2.9 to 4.9 meters (9.5 to 16.1 ft). Weight estimates for an average adult A. fragilis generally range from 1.5 to 2.3 metric tons (3,300 to 5,070 lbs), with some larger individuals potentially weighing up to 2.7 metric tons (3.0 short tons).
The skull of Allosaurus was large yet relatively light, equipped with sharp, serrated teeth. Its jaws contained numerous teeth, with 5 in the premaxilla and 14 to 17 in the maxillae and dentaries. These teeth were continually shed and replaced, making them common fossils. Allosaurus also featured brow horns above its eyes, which varied in shape and size among individuals.
Size in Context
To visualize its scale, an average adult Allosaurus, at 8.5 meters (28 ft) long, was comparable to a typical school bus. The largest individuals, approaching 12 meters (39 ft), could stretch the length of two large cars. Its height, around 4.5 meters (15 ft) at the hip, allowed it to look over a single-story building.
Among its Jurassic contemporaries, Allosaurus was a predator, though not the largest dinosaur. While an Allosaurus typically weighed 1.5 to 2.3 tons, a Stegosaurus, a common prey item, could weigh up to 7 metric tons (15,400 lbs). Despite being shorter than Allosaurus, Stegosaurus had a more robust build. Larger sauropods like Diplodocus dwarfed it, reaching 24 to 26 meters (79 to 85 ft) and weighing 12 to 14.8 metric tons. Allosaurus was also smaller than the later Tyrannosaurus rex, which could reach 13 meters (43 ft) long and weigh 7 metric tons.
What Its Size Meant
Allosaurus’s physical dimensions played a significant role in its predatory lifestyle. Its powerful hind limbs and muscular tail provided propulsion and balance for an active hunter. The ability to open its jaws very wide suggests a feeding strategy using its skull like a hatchet to inflict deep wounds, rather than relying on a crushing bite force, which was relatively weaker than some other large theropods. This “strike and lock” mechanism, combined with its sharp, serrated teeth, allowed it to slice through flesh.
Allosaurus likely tackled large prey, including ornithopods, stegosaurids, and juvenile sauropods. Fossil evidence indicates it hunted live animals and scavenged carcasses. Some paleontologists suggest cooperative social behavior for larger prey, while others propose they were solitary predators that congregated at food sources. Its speed, estimated up to 21 mph (9.4 m/s), aided in ambushing and pursuing prey.