First of all, holy moses, hellbender with quad-post!
If there was no evolution then all animals stay exactly the way they are, then if species dies then no other animal can evolve to it's former niche, then there is a hole in the relationship among the species, then the envionment would be shot, and everything dies.
There is a species that went extinct a long time ago, it is sometimes called a "beardog" I don't remember it's scientific name. Canines (dogs), felines (cats), ratcoons, bears, and other mammals all have very similar bone structure to this creature. Furthermore, the fossils of canines, felines... ect. that are older resemble this creature even more, and the older they are they resemble this beardog. There are millions of other examples.