Evolution never stops at one place. At the basic box you created toxic predators, hided them to the holes, built compound chains of interactions. Your animals accumulated fatty stock, ran into hibernation, rejected tails.
The expansion opens new space for experiments. Now you can hide your animals into strong shells, teach them to emit ink and even to fly. Now, before attacking a harmless animal, it would be better for you to think three times about it. As it can be that it isn't defenseless prey, but a dangerous predator catches you at a bait.
A base version of "Evolution" game gave a possibility to create animals with approximately of 50 thousands of different combinations, but now a number of possible combinations is more than 50 millions. This number is more than number of kinds of living creatures on the Earth.