Scutellosaurus (pron.:"skoo-TELL-oh-SORE-us") is an extinct genus of thyreophoran ornithischian dinosaur that lived approximately 196 million years ago during the early part of the Jurassic Period in what is now Arizona, USA. It is classified in Thyreophora, the armoured dinosaurs; its closest relatives may have been Emausaurus and Scelidosaurus, another armored dinosaur which was mainly a quadrupedal dinosaur, unlike bipedal Scutellosaurus. It is one of the earliest representatives of the armored dinosaurs and the basalmost form discovered to date. Scutellosaurus was a small, lighly-built, ground-dwelling, herbivore, that could grow up to an estimated 1.175 m (3.9 ft) long.
Scutellosaurus was lightly built, and was probably capable of walking on its hind legs. It had an unusually long tail, possibly to provide a counterbalance against the weight of the armored body, and long arms that suggest it may have browsed on all fours. It was around 1.2 metres (3.9 ft) long, 50 centimetres (20 in) tall at the hips, and weighed 10 kilograms (22 lb). The fossil evidence includes two partial skeletons recovered from Arizona, although of the skull only the lower jaw has been recovered. There were also several hundred scutes running along its neck to its back and as far down as its tail. These formed parallel rows, with as many as five rows on each side. It also had double rows of scutes, or external plates, running neck to tail. Some of these shields were flat, while others were pitted.