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

Use tranq darts instead of arrows if you can, because they will roll up after taking a certain amount of damage and will only take 10% torpor when rolled up