Never fight a Wild Giganotosaurus head on unless you wanna get rekkt!! If you have tamed a low level wild giga e.g 20-85 ish, be careful around Alpha T-Rex’s as they can still pack quite a punch! I nearly lost my level 85 giga because I had no stamina etc.
If one is encountered near water, you can simply lure it out to sea with a flyer and it will swiftly drown. Given the water is deep enough. If encountered inland not near water. Pray to the overseers you have something fast enough to out run it. Then promptly die because they're as fast as a mad Hispanic mother with a shoe. Not as deadly as one though.