Utah Fossil

Theropod Dinosaur

(Allosaurus fragilis)

Adopted in 1988.

The Theropod Dinosaur, Allosaurus fragilis,  was designated the State Fossil in 1988. There are different meanings of the word allosaurus, "Different Lizard" and "Strange Reptile," are two examples. Allosaurus was a carnosaur, one of the groups of theropod meat-eaters. This animal was large and probably too bulky to move at speed over any distance, however, the large sauropods and stegosaurs on which it fed were not fast-moving themselves.

One of the largest Jurassic Carnosaurs of North America. An average Allosaurus weighed about 4 tons (3.6 metric tons) and measured 35 feet (10.5 m) from the tip of its nose to the end of its TAIL. The largest known was 45 feet (13.5 m) long. When Allosaurus stood upright, it was 16.5 feet (5 m) tall.

Allosaurus was a carnivorous "lizard-hipped" dinosaur or theropod. It had a bony red crest above each eye, a strong s-shaped neck. Its teeth were 5-10 cm long and curved backward with serrated front and back edges. Allosaurus' strong back and neck aided its jaws in tearing off chunks of flesh.

Like all Theropods, Allosaurus Walked on two legs with its heavy tail stretched out behind for balance. Its strong legs were built for speed; they had powerful muscles and heavy bones. Although its arms were short, each finger on its three-fingered hands was armed with a sharp claw that could be up to 6 inches (15 cm) long. The three long toes on its feet were equipped with eagle-like talons.

This meat eater had a strong neck. Its huge 3-foot (90 cm) long head had heavy bony knobs, or ridges, above its eyes; its enormously powerful jaws were filled with saber-like teeth 2 to 4 inches (5 to 10 cm) long. The jaws were hinged like those of a snake, so Allosaurus would have been able to swallow huge hunks of meat whole. Scientists have found APATOSAURUS vertebrae with Allosaurus tooth marks on them, evidence of a Jurassic feast! Although not really built for speed, it had two sturdy legs and a powerful tail. It was a fearsome predator of its time.

The genus Allosaurus is based on the virtually complete skeleton discovered by M. P. Felch in 1883.

More than 60 complete and partial Allosaurus skeletons have been recovered from the Morrison Formation between Wyoming and New Mexico, in the USA. It is the largest and most common carnivore found in these widespread deposits. At the Cleveland Lloyd Quarry in Utah, USA, Allosaurus is by far the most numerous fossil type and is represented by at least 44 individuals. These ranged in size from adults to juveniles.
 

Geologic Time: 145 to 150 million years ago (Late Jurassic)

Geographic Range: Wyoming, Montana, Colorado, New Mexico, South Dakota, Utah, and Oklahoma

Adult Weight: 1.5 - 2 tons

Adult Length: 30 - 40 ft long

Habitat: Plains and lowlands

Diet: Meat

Characteristics: Allosaurus was the most common large carnivore of the Late Jurassic in North America. It was a smaller predecessor of the Cretaceous Tyrannosaurus. Strong forelimbs with sharp claws, powerful hind legs and recurved, dagger-like teeth are evidence that Allosaurus was a formidable predator. Although it was much smaller than sauropods like Apatosaurus (Brontosaurus), which were also common at the time, quite possibly Allosaurus hunted in packs to bring down larger prey. Like many meat eaters, it may also have been a scavenger.

Many Allosaurus specimens representing individuals of different ages have been recovered in exposures of the Morrison Formation in the Rocky Mountain West. This specimen is interpreted as a subadult.