I have tamed 2 of these guys when I was around lvl 35-40s. Find some near rivers, find a good rock and shoot them (with tranqs of course) to knock them out. It helps to have a flier eg. pteranodon to move between rocks.

You can also use your pteranodon’s twirl ability to hit low level Spinos in mid-air so a higher level may spawn in it’s place.

Good luck! I hoped this helped :)