They no longer collect obsidian. I tried it earlier and i only got stone. This is as of the latest patch adding the megatherium

The new update reduced the weight of stone on this bad boy by 75% *BUMP*

Be sure to shoot the doedicurus on it's underside, not the shell, the shell only takes half torpor

Just grab it with an argy and have your friend shoot it while in your claws.. stops it from rolling up, easy ko.