An Ankylosaurus was a massive, plant-eating dinosaur that lived about 68 to 66 million years ago, near the end of the age of dinosaurs. Picture a creature built like a living tank: low to the ground, covered in thick armor plating, and roughly the size of a modern military vehicle, stretching up to 30 feet long and weighing as much as four cars.

The Ankylosaurus had bony plates called osteoderms embedded in its skin, creating a natural shield that protected it from predators like Tyrannosaurus rex. Even its eyelids had armor. But its most distinctive feature was the massive club at the end of its tail, made of fused bone and capable of delivering devastating blows. Scientists believe an Ankylosaurus could swing this club hard enough to break the leg bones of an attacking predator.

Despite its fearsome defenses, the Ankylosaurus was a peaceful herbivore that munched on low-growing plants. Its name comes from Greek words meaning “fused lizard,” referring to the way many of its bones were fused together for extra strength. When paleontologists discovered the first Ankylosaurus fossils in Montana in 1906, they realized dinosaurs had evolved some of the most creative defensive strategies in Earth's history.