If having trouble finding one in the swamps try bringing a parasaur with you and use its detection ability to see all nearby carnivores hiding in the water and walk up to them to check if they are a diplo. as long as you have some sarcos or barrys to clear out the piranhas you will find one in a couple of minutes easy.
I happened to go prime meat shopping and scoop him up. Never seen one before. Loved it. Found a mate! Made them mate! Egg sit it in the water... baby Explode. Lmaoooooo never have I ever seen a Dino explode before. Was so piss off... I laughed...went to bed. Lol