Kerrigan can again encounter a ravasaur when she covers the final distance to kill Slivan. Five or six of them stand on high ground where Kerrigan can't reach them. She will have to use leaping strike to get to them and take them out, otherwise her primal zerg army will only come to the other side damaged.
On hard/brutal difficulty they will also spawn as minions during the boss fight with Slivan, and later during the boss fight with Zurvan.
When killing the ravasaurs on the high ground waiting to ambush the player on normal difficulty they will not respawn. When killed on hard or brutal difficulty they will respawn after a short time.