Simply releasing herbivores amongst guests won't do the trick, they need to be panicking. They they are one of the few with the highest comfort threshold for herbivores (60%). If you've followed the walkthrough to a tee, you won't have released this species yet. Incubate a pair of Polacanthus at the new Creation Lab.
The setup is complicated and a little random and the achievement itself seems a little buggy. You need to photograph a Herbivore attacking a guest and it's a little trickier than you might expect. If you unlocked it way back on Isla Matanceros, release and immediately sell a single Polacanthus then skip ahead.
