Ankylosaurus is a genus of dinosaur belonging to the group Ankylosauridae. It lived during the Late Cretaceous period, approximately 68 to 66 million years ago. The first fossils of Ankylosaurus were discovered in the early 1900s in what is now Montana, USA. Among the numerous dinosaurs discovered and named by the renowned paleontologist Barnum Brown was Ankylosaurus.

Ankylosaurus gives its name to the group to which it belongs to - the ankylosaurs. Its name originates from its skeleton which is bony by its nature.

Ankylosaurus was a large, heavily built dinosaur, measuring around 20 to 33 feet (6 to 10 meters) in length and weighing approximately 4 to 6 tons. Its most striking feature was its extensive armor, consisting of large bony plates called osteoderms embedded in its skin, providing protection against predators.

Ankylosaurus was distinguished by its notable armor, comprising bone knobs and plates known as osteoderms or scutes, which were embedded in its skin. While the exact arrangement of these osteoderms remains uncertain as they have not been found in articulation, inferences can be drawn from related animals, leading to various proposed configurations. The osteoderms ranged in size, from small 1-centimeter (1⁄2 in) diameter knobs to larger ones measuring up to 35.5 cm (14 in) in length, with varying shapes. Typically, the osteoderms of Ankylosaurus were thin-walled and hollowed on the underside.

Additionally, Ankylosaurus sported a distinctive tail club made of fused bones, which it likely used as a powerful weapon for defense against predators or intruders.