If you are going to tame one of these with no dinos, be sure to upgrade your movement speed and get tranqs. When you see it whip its tail forwards move to the right you will dodge the shots. This worked for me.
I tamed my first thorny by simply being on a rock ledge above it, paying close attention if any tail spikes were thrown and dodging easlie. The ledge took most of the hits and I used trank arrows to take it down. I didn't know what it ait so threw in everything. Meat, they like meat. So that's how I got my boy, Chibi.
Super cute, they eat raw meat(I thought they just ate berries and were a passive tame) don’t approach them they will throw their quills on their tails at you(learned that the hard way) they make noises that will make you think your going crazy, but tranq them an then you have a thorny baby
If you have a flyer carry one to a taming pen, it's gonna aggro and start throwing spines at everything it sees the minute it lands. Plan accordingly, and use solid walls so it can't shoot through them.