The JTT scenarios work that you achieve a goal at a time to obtain new animals etc for the next goals.
With the ice age scenario, you should have 2 yeti's available to you to start with (wandering around the zoo). You also have some other ice age animals there you can adopt to fufill requirements.
You will find once you ahieve those goals, the other animals required will become available to you.
That is why you can't see them there at the beginning of the scenario.