Monoclonius

Monoclonius, also known as centrosaurus, was a species of dinosaur.

Description
Monoclonius resembled a triceratops, but instead of three horns it only had one, in the center of their bony head crest. It had very thick skin. Its head was very flexible, allowing it to turn it rapidly.

Combat
Their horn was strong and sharp, giving them an effective natural weapon against predators. Their skin was thick enough to protect them from all but the sharpest claws. For small predators, a herd of monoclonius tended to merely stampede over them.

Biology
Monoclonius were herbivores and lived in herds.