Passive tame; Sneak up on one and have taming food in you bar. It'll take you on a wild ride on it's back, run into all other creatures and aggro them if you're unlucky.
I recommend to tranq them, then build a wall around it. That way, when it wakes up, it can't run around like crazy. You'll need to feed it tame food whenever it asks for it while you're on it's back, or you'll fall off eventually.
To tame one of these creatures, you would need berries or crops. The best is just Rockarrot. Approach one with the feeding item on the last item slot. Feed it and ride it. You'll need to press the action button (E for PC players) for everytime they stopped moving or the icon on the right flashes, prompting you to use it.
To get a 100% taming efficiency on this creature, avoid spamming the buttons and carefully timing your action button. Make sure that your surroundings are clear and there are not too many threats. They often run off into random areas that tends to be near a Giga territory.
They often spawn in large open fields so that is best to look for one. Good luck and have a good one.
I would not recommend taming a high lvl. If you have the resources, by no means go ahead and get him but I found out recently that it takes an absolute butt load of Rockarrots (100 for a lvl 95) to tame him. It took a very long time and in the long run, I didn’t even get him. Not to mention, you have to have extreme focus not to let him buck you off and lose taming progress for that long of a time.