In case you have difficulty with killing trikes, and you have leveled up to the point of firearms such as the shotgun, here is my advice.:

First of all, Triceratops have resistance to damage for their head, but nowhere else on the body, so if one is charging you, you can shoot it in the leg for massive damage.

Second of all, before engaging, move the the side of the trike, load your shotgun fully, and then shoot it twice in quick succession in the chest with the shotgun, followed up by a longneck rifle shot as well. Try to keep to its side profile so that it cannot attack you, but you can attack its unarmored spots.

Third of all, keep a large distance between you and it so that it cannot easily charge you and stun you, and so you can avoid the strike if it attempts to do so.

More Triceratops Encountering Tips