I do not believe they would likely fight each other often, as for both are herbivores. But part of me speculate if triceratops was actually more aggressive at times, sort of like a modern cape-buffalo or even a hippopotamus. At the same time, I question if ankylosaurus was aggressively defensive like a rhino and would threaten things around it quite often; generally a defensive loner that prefer to be alone.





If my speculations are correct, a fight between them would likely be the intentional or unintentional result of the triceratops getting too close.

However, if they fought (which they likely would not, due to injuries), the ankylosaurus would have the edge with its taught body armor and smashing clubbed tail (which would shatter bones) while triceratops had size and a head of massive robust horns (that could supposedly even pierce through a car) with a thick frill.