The Argentavis has a weight reduction of 50% for Black Pearls, Crystal, Metal, Metal Ingots, Obsidian, Organic Polymer, Polymer, and Stone, and its saddle acts as a mobile smithy. In terms of how to tame it, I'd recommend taming a Pteranodon and setting up a trap near the Argy you want to tame, as both of these will make taming the Argy MUCH easier.

A good trap is made with 4 stone dino gateways and 2 reinforced dino gates. Place 3 of the gateways close to each other in a straight line, making sure you can go through all 3 of them in a straight line, but place the 4th one a little farther away from the others. This is so your Pteranodon can fly through the gap, but make sure you only have enough space for your Pteranodon, as you don't want the Argy escaping. Once you've made sure your Ptera can fly through that small gap, place a reinforced dino gate on the front and rear gates. The front is the one that has two others behind it, and the rear gate is the one that's farther away from the others. Open up the front gate, mount your Pteranodon, and lead the Argy you want to tame into the trap, flying out of the gap you left. Then quickly land, get off your Ptera and close the front gate. Congrats! You've trapped an Argentavis! Now good luck taming it!

More Argentavis Taming & KO Tips