I found that the easiest way to tame one of these is with a griffin since you can basically shoot through the griffin and the turn radius helps a whole lot so just fly up and shoot away. Oh and try to have a high dmg crossbow. I had a 485 dmg asc one it takes about 30-40 arrows for a lvl 30 giga depending on your aim and the chase he gives you.

More Giganotosaurus Taming & KO Tips