Scutellosaurus ( ) is a 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, lightly-built, ground-dwelling, herbivore, that could grow up to an estimated long. Etymology The genus name Scutellosaurus means "little-shielded lizard", and is derived from the Latin word "scutellum" meaning "little shield", and the Greek word "sauros" (σαύρα) meaning "lizard". The type and only valid species known today is Scutellosaurus lawleri. The specific name honors David Lawler who collected the fossil. Description 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. It was a relatively small dinosaur, measuring in length and in body mass. The fossil evidence includes several partial skeletons recovered from Arizona by the Museum of Northern Arizona and the University of California Museum of Paleontology, although the skull is poorly known from these specimens. There were several hundred osteoderms 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 osteoderms, or external plates, running neck to tail. Some of these shields were flat, while others were pitted. Discovery and occurrence The holotype specimen of Scutellosaurus lawleri (MNA.V.175) was recovered at the West Moenkopi Plateau locality in the Silty Facies Member of the Kayenta Formation, in Coconino County, Arizona on the land of the Navajo Nation. The specimen was discovered and collected by David Lawler in red claystone sediments that were deposited during the Sinemurian stage of the Jurassic period, approximately 196 million years ago. The holotype specimen was described by Edwin Colbert (1981) based on the following: partially preserved premaxillae with teeth, a right maxilla with seven teeth, a left maxilla with five teeth, dentaries that are missing their posterior portions, a left dentary with 18 teeth, a right dentary with 10 teeth, other skull fragments, 21 presacral vertebral centra, several