same process each time: ride the dino onto the ring, jump off and step on the ring to activate.
Failed: Terror Bird, Gigantopithecus
Success: Parasaur, Quetz, Rhino, Argentavis, Carno, Ankylo, Beezlebufo, Bronto, Dimo, Mammoth

gonna try to find if there are any other dinos

sry for my general "doesn't work". I should know better and test before claiming such