The ankylosaurus was a dinosaur of the Cretaceous Period whose fossils have been found in western North America. Its well-armoured spiky body and club-like tail, and low-slung frame make it immediately recognisable among dinosaur fans. Its length has been estimated at somewhere between 6.25 and 9 metres (20.5-30 feet). The ankylosaurus was part of a family of reptiles known as ankylosaurids, all of whom were herbivores, biting rather than chewing their food.
Its armour consisted of large plates and knobs of bone known as osteoderms embedded in its skin, similar to the armour found in crocodiles, armadillos, and some lizards. The osteoderms may also have been overlaid by keratin. The ankylosaurus also had a bony club protruding from its tail, where osteoderms were fused to its vertebrae.
The ankylosaurus survived until the great Cretaceous-Tertiary extinction event, and fossils have been found in Montana and Wyoming in the US and Alberta, Canada. The first fossil anylosaurus was found and named by American paleontologist Barnum Brown in Montana in 1906.