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.
Just run under the legs make sure you have mejos (having a harvesting animal is a good way to get them) and then you have got a diplodocus! They are great harvesters they have great weight so you can carry a lot on them but be aware they can attract carnivores the saddle is expensive but wort for a tribe holds 10 people but is expensive