Little late but... if you build a 1x1 (3 walls 1 door) then add a doorframe ontop of each wall and a ceiling ontop of that you have a reverse taming pen! Stand inside and agrro it and wait for it to be able to be shot through the doorframes. It cant shoot you but you can shoot its head. Easy tsme!
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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.