Bring wooden pillars near the base of a mountain or large rock, so when the wild morellatops walks into a corner, you can pillar it off. Be careful with slopes, because if the wooden pillars are too short, he will just glitch over/through them. Bring an argy with you when you're taming one, to defend it from any wild carnivores.
In a group they attack, individual they run. Pick the lone wolf and lead it by facing the way you want it to go and trap it against a wall or rock or a safe place. No missed shots, no wasted resources, and a easy Morrelatops tame.
If you find yourself against a herd of these, just keep backing up and using your boomerangs, trans arrows, and slingshots. Both the primary and secondary attacks have a delay before they actually deal damage, and they have to stop moving first, so if you keep backpedaling they won't be able to hit you.