Allosaurus

Basic Information

Allosaurus belongs to a family of dinosaurs called Allosauridae, and its name means “different lizard” because its vertebrae were different from other dinosaurs known when it was discovered!

Allosaurus lived during the Late Jurassic period, about 155 to 145 million years ago, which was about 80 million years before Tyrannosaurus Rex!

The first Allosaurus fossil was discovered in 1877 by Oramel Lucas in Colorado and described by Othniel Charles Marsh in the same year. Since then, over 60 specimens have been found!

A fully grown Allosaurus could reach lengths of up to 32 feet (9.7 meters), about as long as a school bus.

Scientists have found Allosaurus fossils in North America, Portugal, and Tanzania, showing these dinosaurs lived in many different parts of the world!

An adult Allosaurus could weigh up to 4,400 pounds (2,000 kg), which is about the same as a modern-day rhinoceros!

Allosaurus was a carnivore (meat-eater) and was one of the top predators of its time, hunting other dinosaurs for food!

Scientists estimate that Allosaurus could run at speeds of up to 21 miles per hour (34 kilometers per hour), about as fast as a horse trotting!

The most complete Allosaurus skeleton ever found is nicknamed “Big Al,” and it’s 95% complete!

Allosaurus is part of the theropod group of dinosaurs, which includes other famous meat-eaters like Tyrannosaurus Rex and modern-day birds!

Physical Features

Allosaurus had a large skull that could reach up to 3 feet (0.9 meters) in length, about the size of a kitchen counter!

An Allosaurus’s brain was about the size of a hot dog, which was actually quite large for a dinosaur of its time!

Allosaurus had about 32 sharp, serrated teeth that were constantly being replaced throughout its lifetime, just like sharks today!

The arms of an Allosaurus were short but strong, with three fingers on each hand ending in sharp claws up to 7 inches (18 centimeters) long!

Allosaurus had special grooves in its skull that helped make its bite stronger, allowing it to open its mouth extremely wide like a snake!

Allosaurus had hollow bones like modern birds, which made it lighter and more agile despite its large size!

The tail of an Allosaurus made up almost half of its total body length and helped it balance while running and hunting!

Scientists have found that Allosaurus had sharp ridges above its eyes, which might have been brightly colored to attract mates!

Hunting & Defense

Allosaurus hunted by ambushing its prey, using its powerful legs to chase down smaller dinosaurs!

Allosaurus didn’t have the strongest bite, but it had a clever way of hunting! Instead of crushing bones like T. rex, it used its sharp teeth and powerful neck to slash at its prey, cutting deep wounds to bring them down.

Fossil evidence shows that Allosaurus sometimes fought with Stegosaurus, and scientists have found Allosaurus bones with puncture wounds from Stegosaurus tail spikes!

Allosaurus could open its jaw up to 79 and 92 degrees, wider than most other predatory dinosaurs!

Habitat & Environment

During the time of Allosaurus, North America was much warmer and more tropical than it is today!

Allosaurus lived in environments that included forests, floodplains, and semi-arid regions with seasonal rainfall!

The Morrison Formation, where many Allosaurus fossils are found, was once a vast plain with rivers, lakes, and seasonal dry periods!

Allosaurus shared its habitat with many famous dinosaurs including Stegosaurus, Diplodocus, and Apatosaurus!

The plants during Allosaurus’s time included giant ferns, cycads, and tall conifers, but no grass or flowering plants!

Allosaurus lived in areas that experienced seasonal droughts, which might explain why so many fossils are found near ancient water sources!

The climate during the Late Jurassic period was generally warmer and more humid than today, with no polar ice caps!

Discovery & Fossils

The first Allosaurus bones were so well preserved that scientists could study the marks where muscles attached to the bones!

Over 60 different Allosaurus specimens have been found, making it one of the best-understood large predatory dinosaurs!

The Cleveland-Lloyd Dinosaur Quarry in Utah has yielded over 46 Allosaurus specimens of all ages!

Scientists can tell how old an Allosaurus was when it died by counting growth rings in its bones, just like tree rings!

Some Allosaurus fossils show evidence of injuries that healed while the dinosaur was alive, proving they could recover from serious wounds!

The most complete Allosaurus skeleton, “Big Al,” shows evidence of 19 different injuries or infections!

Scientists have found Allosaurus teeth marks on other dinosaur bones, helping us understand what they ate!

Recent discoveries of Allosaurus eggs in Portugal have helped scientists understand how these dinosaurs reproduced!

Fossil trackways show that Allosaurus walked with an upright posture, holding its tail off the ground!

The name “Allosaurus” was chosen in 1877, but it wasn’t until 1920 that scientists really understood what this dinosaur looked like!

The first complete Allosaurus skull wasn’t found until 1908, over 30 years after the dinosaur was named!