Allosaurus, a large predatory dinosaur, roamed the Earth during the Late Jurassic period, approximately 155 to 145 million years ago. It was a dominant predator, with many fossil remains unearthed across North America, particularly within the Morrison Formation. Its scientific name, “Allosaurus,” translates to “different lizard,” a reference to the unique structure of its vertebrae.
Measuring Allosaurus
The average adult Allosaurus, specifically the well-known species Allosaurus fragilis, typically measured around 8.5 meters (28 feet) in length. Some individual specimens were larger, with the largest definitive fossil, AMNH 680, estimated to be 9.7 meters (32 feet) long. Fragmentary evidence suggests even larger individuals might have existed, potentially reaching up to 12 to 13 meters (39 to 43 feet), although these larger estimates may sometimes be attributed to different, related genera.
At the hip, an Allosaurus stood approximately 2.9 to 4.9 meters (9.5 to 16.1 feet). The average mass for Allosaurus fragilis is estimated at about 1.7 metric tons (1.9 short tons). Larger specimens could weigh between 2.3 and 2.7 metric tons (2.5 to 3.0 short tons), with some adult weight estimates ranging from 1 to 4 metric tons, reflecting the natural variability within the species.
Allosaurus Size in Perspective
An average Allosaurus, at 8.5 meters (28 feet) in length, was shorter than a standard school bus, which typically ranges from 11 to 14 meters (36 to 45 feet) long. Its hip height, around 3.3 meters (11 feet), is comparable to or slightly taller than a large African elephant.
When compared to Tyrannosaurus rex, Allosaurus was smaller and less massive. A typical T. rex could reach lengths of 12 meters (40 feet) and weigh between 5 to 9 metric tons, making it a heavier predator. Conversely, Allosaurus was similar in length to Stegosaurus, which measured about 9 meters (30 feet) long, though Stegosaurus could be heavier, weighing around 5 metric tons.
Uncovering Allosaurus Dimensions
Scientists determine the size of extinct dinosaurs like Allosaurus primarily by studying fossilized skeletal remains. Since finding a complete dinosaur skeleton is uncommon, paleontologists often use comparative anatomy, relying on well-preserved bones to infer the dimensions of missing parts. By measuring elements such as skull length, the number and size of vertebrae, and the circumference of limb bones, researchers can estimate the creature’s overall length, height, and body mass.
Size estimates can vary due to several factors. These include the completeness of the fossil record, natural individual differences among animals of the same species, and the various methods paleontologists employ for reconstructing skeletons and estimating mass.