Most plant-eaters relied on running, hiding, or hanging in big herds to stay safe. Ankylosaurus had a different strategy: be impossible to bite. It was about 20 feet long, low to the ground, and covered head to tail in heavy bony plates and short spikes - like a living armored tank.
The most famous part was at the back end. Two big fused chunks of bone formed a club at the tip of the tail. Powerful muscles let Ankylosaurus swing that club horizontally with serious force. Computer simulations suggest a full-power Ankylosaurus tail swing could shatter the leg bone of an attacking T. rex - and a downed T. rex was a dying T. rex.
Even its eyelids were armored: a small bony plate could swing down over the eye to keep predators from getting at the one soft target on its body.
