Edmontonia

A small group of Edmontonia graze at dawn while a Quetzalcoatlus warms up to search for food in the background.
While I doubt that armored animals were social (I mean, they're well defended enough, why would they want to gather in groups?), I think these guys would tolerate quite well the presence of other members of their species. Also, note the presence of (speculative) sexual dimorphism. The male has a brighter coloration, as well as longer, sharper spikes, while the females have stumpier shoulder spikes.
Edmontonia ("from Edmonton -actually the Edmonton formation, now Horseshoe Canyon formation"), is a genus of medium sized, bulky, armored nodosaurs notable for their forward-pointing shoulder spikes and rows of protective neck-plates. It measured as much as 6.5 metres long. It is also notable because in many specimens the armor is in virtually the same position as it was in life (as the armor is usually very loosely attached to the bones, and mostly to the skin, the preservation of its position is rare), which it has been theorized is because the animal lived in an environment where qucik weather changes were usual, meaning that when the dinosaur died and dried up due to the drought, it became quickly buried in muddle after a flash flood. It had a narrow skull somewhat resembling that of a calf, which is why I like them, I like to think of them as armored pigs with behaviours switching between those of a cow and of a rhino.