If you playing on mobile it's actually easy to catch one

You need

4 dinos gate way

Around 300 bio toxin for a lvl100 giga (don't spam )

Shooting balm

5 quitzel kibbel

And 200 darts if you have the regular weapon. If you have the ancient one you will need way less then that

A large bear trap

Make a u shape with the gates and put the bear trap in it

Drage him inside (use a petronodon with a hight hp ) and closs it from behind (be quick)

Kepp your distance and start shouting him (don't stop till it's down)

Feed him the shouting balm then give him the kibbel

And it's yours