Come meet our young Allosaurus. He's quite friendly, usually.

He rarely eats visitors.

NAME: Allosaurs fragilis

Meaning: Allosaurus means “different lizard,” named for its unusual vertebrae that have hollow places in some of them. This was different than other dinosaurs known at the time. The hollows may have held air sacs like similar spaces in the bones like modern birds. “fragilis” means fragile, or easily broken.

Pronounced: AL-oh-SAWR-us

By: Othniel C. Marsh, in 1877.

DIET: Carnivore (meat eater) it ate plant eating dinosaurs, like stegosaurus and iguanodonts

SIZE:      Length: about 40 ft (12 m) long

Height: 10 ft (2 m) tall at the hips

Weight: up to 4.5 tons (9,000 lbs)

WHEN IT LIVED: Late Jurassic Period, about 155-145 million years ago


North America and Europe. Fossils have been found in Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah, Wyoming. Arizona has few rocks of the right age. Also Portugal, Europe, and perhaps Tanzania, Africa, and Australia.


Kingdom Animalia (animals)

  Phylum Chordata (having a hollow nerve chord ending in a brain)

    Class Archosauria (diapsids with socket-set teeth, etc.)

      Order Saurischia (lizard hipped dinosaurs)

        Suborder Theropoda (bipedal carnivores)

          Tetanura (advanced theropods with three fingers)

            Superfamily Carnosauria

             Family Allosauridae

              Genus Allosaurus

                Species: Five species are known, plus one type that has not yet been formally described.

                               All the North American species may have been found in Arizona.

  1. A. fragilis Marsh 1877, from North America. The most common species.
  2. A. atrox Marsh 1878, from North America.
  3. A. amplus Marsh 1879, from North America.
  4. A. lucasi Dalman 2014, from North America.
  5. A. europaeus Mateus et al. 2006, from Portugal

“A. jimmadseni”, from Portugal (not yet formally named)


Allosaurus was the most common top predator of its time. It had a huge head, and a mouth that opened extremely widely to expose its sharp, serrated teeth. Its short arms were powerful and built for grasping, it could even hold prey against its body.


Some dinosaurs related to Allosaurus are known to have had feathers, and some have speculated that Tyrannosaurus did too. Most paleontologists now seem to agree that they probably had feathers as young, but adults would have had few if any. They may very well have had a feathery crest running along their back, and perhaps more.


 Allosaurus fragilis portrait show it's wide gape.

Art by Bob Hole


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