Me and my tribe love our lystro. They honestly don’t have any use to us anymore as we have all maxed our levels. But these critters are certainly a nice form of company. To tame them you can take some mejo berries. I believe aquatic mushrooms may work too if you are on aberration.
Don’t Give it a berry because when I did and steal an egg after that I tried to kill it but it turned invincible please let the creators know so you can still hurt a creature when there not fully tamed.
Fun fact the Lystro is an ancient ancestor of mammals. When you see one tame it, they can be very rare. I suggest using mejoberries. These guys are tough, but can't take on fast dinos like Raptors. Trust me I learned the hard way... "Your Lystrosaurus lvl 13 was killed by lvl 23 Raptor".