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.
Doedicurus can farm obsidian and will do a 2x the rate of the anky. This depends on which map you're on. Tested on the island. Can't use on the volcano on rag (tested) will test others when I get chance believe it is map or reign dependent.
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.