''Scutellosaurus'' ( ) is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of thyreophoran

ornithischian Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

that lived approximately 196

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago ...

during the early part of the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

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 Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor ...

dinosaur, unlike

bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

''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 A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

, that could grow up to an estimated long.

Etymology

The genus name ''Scutellosaurus'' means "little-shielded lizard", and is derived from the

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

word "scutellum" meaning "little shield", and the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

word "sauros" (σαύρα) meaning "lizard". The type and only valid

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

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 Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

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

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amp ...

s 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

s, or external plates, running neck to tail. Some of these shields were flat, while others were pitted.

Discovery and occurrence

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

specimen of ''Scutellosaurus lawleri'' (MNA.V.175) was recovered at the West Moenkopi Plateau locality in the Silty Facies Member of the

Kayenta Formation The Kayenta Formation is a geological formation in the Glen Canyon Group that is spread across the Colorado Plateau province of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Traditionally has been suggested ...

, in Coconino County,

on the land of the

Navajo Nation The Navajo Nation ( nv, Naabeehó Bináhásdzo), also known as Navajoland, is a Native Americans in the United States, Native American Indian reservation, reservation in the United States. It occupies portions of northeastern Arizona, northwe ...

. The specimen was discovered and collected by David Lawler in red claystone sediments that were deposited during the

Sinemurian In the geologic timescale, the Sinemurian is an age and stage in the Early or Lower Jurassic Epoch or Series. It spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago). The Sinemurian is preceded by the Hettangian and ...

stage of the

period, approximately 196 million years ago. Scutellosaurus lawleri

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 complete and partial neural arches and spines, five sacral vertebrae, 58 caudal vertebrae with neural arches and several chevrons, several incomplete ribs, both scapulae, both coracoids, partially preserved ilia, fragments of the pubic bones and of the ischia, both humeri, the distal end of the right radius, the proximal and distal ends of the left radius and ulna, fragments of the manus, both femora, the right tibia, the proximal end of the right fibula, the right astragalus, the left tibia, the left fibula, various bones of the pedes, including a possible distal tarsal bone, and over 300 osteoderms.''The Illustrated Dinosaur Encyclopedia'', D. Dixon, 1998 (

References

{{Taxonbar, from=Q131646 Early Jurassic dinosaurs of North America Thyreophorans Fossil taxa described in 1981 Taxa named by Edwin H. Colbert Paleontology in Arizona Kayenta Formation Ornithischian genera