Allosaurus, a prominent bipedal predator, roamed Earth during the Late Jurassic period, approximately 155 to 145 million years ago. Its name, meaning “different lizard,” refers to its unique hollowed vertebrae, a feature that distinguished it from other dinosaurs known at the time of its discovery in 1877. As a large theropod, Allosaurus stood as a significant carnivore in its ecosystem, with its fossil remains predominantly found in North America’s Morrison Formation.
Typical Dimensions of Allosaurus
The most recognized species, Allosaurus fragilis, typically reached a substantial size. An average adult measured about 8.5 meters (28 feet) in length. These animals stood approximately 2.9 to 4.9 meters (9.5 to 16.1 feet) tall at the hip. Weight estimates for an average Allosaurus fragilis adult range from around 700 kilograms (1,500 pounds) to 1,000 kilograms (2,200 pounds).
Larger individuals of Allosaurus fragilis could exceed these average measurements. The largest definitive specimen, AMNH 680, is estimated to have been around 9.7 meters (32 feet) long. Weight calculations for such larger specimens suggest they could reach between 2.3 to 2.7 metric tons (2.5 to 3.0 short tons).
Unearthing the Allosaurus’s Scale
Paleontologists rely on fossil evidence to reconstruct the size of extinct dinosaurs like Allosaurus. This process involves meticulous examination of skeletal remains, often piecing together fragmented bones to form a complete picture. Comparing these fossil bones to those of related, more complete specimens or even modern animals provides crucial insights into overall body proportions.
Estimating length typically involves measuring the skull and the series of vertebrae, accounting for the intervertebral discs that would have been present. For weight, scientists use methods such as analyzing the circumference of leg bones or creating fleshed-out scale models. Muscle attachment scars on the bones also offer clues about the musculature and approximate bulk of the animal. While these methods provide estimates, the incomplete nature of many fossil finds means that some degree of estimation and variation in results is inherent.
Diverse Sizes and Record Holders
The size of Allosaurus was not uniform across all individuals, exhibiting natural variation influenced by factors such as age and species within the genus. Fossil discoveries, like those from the Cleveland-Lloyd Dinosaur Quarry, show a wide range of sizes, from juvenile specimens less than 1 meter long to adults reaching up to 12 meters. This diversity highlights the growth stages and individual differences within Allosaurus populations.
Beyond typical Allosaurus fragilis specimens, some exceptionally large allosaurids have been discovered. Historical estimates suggested some individuals could reach 12 to 13 meters (40 to 43 feet) in length. Another notable large form, Saurophaganax maximus, is estimated to have measured approximately 10.5 to 10.9 meters (34 to 36 feet) long and could weigh around 4 metric tons. These larger finds highlight the potential for greater sizes within the Allosauridae family.