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.
I don‘t know why so many people say that the doedicurus can‘t gather obsidian...today i noticed: he can...and way better than the ankylo...on obsidian rocks next to the volcano (the island). Probably after a patch i didn‘t realize