Means: Different Lizard

Period: Late Jurassic, 155-145 Million Years Ago

Region: Western North America and Europe (Portugal)

Allosaurus was named and described by the American palaeontologist Othniel Charles Marsh in 1877, on the basis of fragmentary remains including a single fossil tooth and a toe bone.  The subsequent discovery of many thousands of fossils including nearly complete skeletons, most famously from the Cleveland-Lloyd Dinosaur Quarry in Emery County, Utah, has made Allosaurus one of the best-known of all the big meat-eating dinosaurs.  Size estimates vary but it may have grown to more than 12 metres in length and weighed around 2.5 tonnes.

A powerful predator of other dinosaurs, Allosaurus possessed a strong but light skull.  All the teeth in the jaws were serrated and its arms, although short, ended in three fingered hands.  Each finger had a long, curved claw, the largest of which measured around 15 cm.

In 1988, in recognition of the abundance of Allosaurus fossil material excavated from the Cleveland-Lloyd Dinosaur Quarry, Allosaurus was appointed the state fossil of Utah.

Several species of Allosaurus have been erected since it was first scientifically described, although most palaeontologists recognise just three species, the most recent of which to be named is Allosaurus jimmadseni (2020).  This species was named in honour of James H. Madsen Jr. the first state palaeontologist of Utah.