Ankylosaurus Dinosaur was the last, main, and most famous of the armored dinosaurs known as the Ankylosaurians. Its back and sides were covered with a stiff shell of armor, but its underbelly was uncovered. It also had a great club-like tail that might be used for defense against predators. Ankylosaurus was about the size of an elephant, but had a low-slung, extremely wide body.