On PS4 I tried to test it's obsidian gathering since it is "Rank 1", well all it was gathering was stone. So I went to another saying maybe something was wrong, NOPE it does not gather obsidian. Just use an Anklyo for that.
Equip your Doedicurus with a saddle, pick it up with an Argentavis and fly near rocks as it automatically harvests the stone as you fly. Level up the melee damage to harvest more stone with each swing. Level up your Argentavis’ weight capacity be an insane stone harvest team.