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".