Get 4 stone gateways and place them in a box shape with a large bear trap in the middle, and place the gates in closed, except for one. Get on a flyer, you need a flyer with good health or this thing will kill it easy, and get the Chicken to chance you on the flyer into the trap. It will get stuck on the bear trap, and you can close the last gate. You need the flyer to get out yourself. Build a 3 wall high tower of stone or metal next to the trap with a roof on top, so you can stand and shoot into the trap. Be carful if you are using a gun or crossbow not to open the gate, I’ve made that mistake before. Once it’s out, a balm is basically required for high leave ones, and you can get a free 10x balm from the megapiranha pursuit, so I recommend saving it for this. They are amazing mounts, so even though it will take a while, it is 100% worth it.
Therizinos are very hard to tame since they are fast and very strong. Plus they aggro once close by it which we all know happens to us. So try to get a high ground which means no close combat only ranged. Meaning no fists and clubs. Only bows, cross, or a compound bow. With tranq arrows. Or darts if you can make a longneck. Once knocked it will take awhile with mejo or crops. But Have a lot of narcotics or narcoberries if you have a harvesting dino with you.