Ankylosaurus

Although its name means “stiff lizard,” it was also known as an “armored dinosaur.” It lived in humid regions where it fed on low-growing vegetation such as ferns and grasses. Its stocky build allowed it to confront predators. Its back, flanks, neck, and tail were covered in thick armor made of numerous flat, interlocking bony plates and spikes.
At the end of its tail was a bony club formed by the fusion of osteoderms, vertebrae, and tendons. This club could break bones.
Bony protrusions around the eye sockets helped protect its head. The bones of its skull were fused with other parts of the skeleton, making it more resistant.
Only the underside of its body lacked any defensive system, which is why it is believed that it would lie down flat during attacks to be completely protected.