Ok so these might seem a monster to you, but these are actually the ultimate gatherers in the mid game, to tame this follow these steps:

1. Use the 4 stone gateway/2 door trap( make sure that you don't take more than 1 hit since 2 hits will murder you).

2. If you don't have much weapons, then use 2 primitive crossbows to knock it.( trust me 2 prim crossbows with 180+ tranqs is enough for a 270 theri )

3. I suggest using a balm or bring at least 150 bio toxin.

4. 3x balm with berries and toxin is enough.

5. Enjoy your theri.