Try using keeping a tanky creature between you and them to soak the quills they throw at you. I had used my Megatherium with 20K health and all I needed to do was peek her shoulder and shoot over it while her tummy was filled with quills. If they have a line of sight on you, they will aim for you and snipe you.
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You don’t need to trap this to tame, it’s a solo tame. If you run up to it, it will go into turret mode then you need to walk circles around it and keep hitting with tranq until it eventually tries to walk away *in turret mode so really slow walking*
Make a 2x2 cage with ramps and a door. Lure the velonasaur in with a flyer. If you stay close to him he won’t enter turret mode. Leveling melee raises his projectile hit points. Also level stamina to attack longer. A high level can shred everything I’ve come across. Can’t wait for an imprinted one for the speed bonus.