Taming these the best trick I learned is load up on Mejo Berries and Chase it's tail. It will spin in circles but this causes it to get hungry significantly faster than just waiting under it, or letting it push you into a rock or cliff or trapping it.

Using the Diplo- the Diplo has a nice use early game in traversing the map. Only large dinos will Aggro the diplodocus allowing you to swim in areas aggressive waterline would kill you. I used mine extensively in the swamp to gather rare flowers, and various seeds as almost nothing attacks them. Seeing as they don't do damage even if you accidentally hit another dino it won't become aggressive. I avoid redwood on them as thylas on the ground can't dismount you, but in the trees they can and will. They are awesome for taming other dinos as you can utilize them in 2 different ways. You can knock out the dino you want to tame, mount the diplo and dismount on top of it don't jump off. Dinos will aggro on you instead of the dino your taming, and you can safely kill them from its back just make sure you don't have your diplo to flee or you'll fall off. Since they don't do damage you can level one up with crazy high heath and send them to attack a large dino, the diplo will keep them occupied without damaging them so taming effectiveness doesn't drop. Since they do knock back on attack it also slows down how fast a dino can kill them. Dinos larger than Carnotaurs will attack you and if you get to close to a tickle chickens it will also attack. Alpha Variants of Raptors and Carnotaurs will not attack the Diplodocus. Early Game they are amazing IMO as they safely open up alot more of the map than any other Dino you can tame and mount at that point.