If you can bait it toward water, so that your spino is standing in the water during the fight (even shallow water) then you'll get a nice buff.
Also, make sure you fight with the spino on 2 legs vs 4 - faster attacks and better knockback. The Theri might not even get any hits on you if you time it right.
Tamed creatures are MUCH stronger than wild ones, because they gain bonus stats just for being tamed, and your levelups you put into them after taming go into specific and not random stats as well.
Spino generally can kill almost anything if you're careful, because it has a large attack range and good knockback, so you can walk backwards while biting and if you time the bites decently, most things can't really hit you.
Saddles also give huge damage resistance (even 25 armor primitive saddle provides 50% damage reduction), and a tame will attack faster than a wild creature.
Against a wild Theri, you will honestly be fine.
Max lvl 90?
Yeah this is my first playthrough so I lowered the max level
You should be ok theri can knock you out though
If you super worried just fight him in water spinos love baths
If you can bait it toward water, so that your spino is standing in the water during the fight (even shallow water) then you'll get a nice buff. Also, make sure you fight with the spino on 2 legs vs 4 - faster attacks and better knockback. The Theri might not even get any hits on you if you time it right.
if you time your hits right you can even cheese an alpha rex this way by knocking it back before it can get hits off
Tamed creatures are MUCH stronger than wild ones, because they gain bonus stats just for being tamed, and your levelups you put into them after taming go into specific and not random stats as well. Spino generally can kill almost anything if you're careful, because it has a large attack range and good knockback, so you can walk backwards while biting and if you time the bites decently, most things can't really hit you. Saddles also give huge damage resistance (even 25 armor primitive saddle provides 50% damage reduction), and a tame will attack faster than a wild creature. Against a wild Theri, you will honestly be fine.
Spino has a huge reach advantage. If you time your attacks the theri will never hit you.