Taming this is easy as pie and takes as long to do as making a pie, unless you got kibble.... Just check how much berries it's gonna take to tame get as much extra as you can, double is most recommended Also get food and water for yourself depending on the level you can be there taming it for 3 in game days Once you feed it it's gonna start pushing you and you tames around so leave them somewhere out of reach, Since they take so long to tame get them to the beach or somewhere else safe with a source of water nearby. If you run out of berries no worries, this tame does not forget your tame progress soon. You can be far for 2-4 minutes before it's tame progress resets or it's when it leaves your immediate area or when it fights Now at first it's gonna be cute when it pushes you around like a cat toy but after a while it gets annoying. To remove this effect entirely run between it's two front legs under its belly. It'll continue pushing you but you'll be out of it's affect area and then
Don't bother knocking it out. Jist get your back against a stone and make the diplo come right above you. The gap between the first two feedings will be huge so be prepared to sit in front of your screen for a while
When taming to make it easier stand against a cliff or a good sized rock. I tamed one for my brother and it was a piece of cake with that technique. Also if you find that the place you find the diplodocus isn’t safe just get near it and lead it away. They won’t hurt you they just like to swat you around like they are playing a game of soccer.