Ankylosaurus was a huge armored dinosaur, measuring about 25-35 feet (7.5-10.7 m) long, 6 feet (1.8 m) wide and 4 feet (1.2 m) tall; it weighed roughly 3-4 tons.
Its entire top side was heavily protected from carnivores with thick, oval plates embedded (fused) in its leathery skin, 2 rows of spikes along its body, large horns that projected from the back of the head, and a club-like tail. It even had bony plates as protection for its eyes. Only its under-belly was unplated. Flipping it over was the only way to wound it.
Ankylosaurus had four short legs (the rear legs were larger than the front legs), a short neck, and a wide skull with a tiny brain.
Sketch from 2008