Life forms will gradually change over time. Life begins as single cells about 1.3 Billion Years ago. Humans arrived about 1.6 Million Years ago. Most of the life that has evolved has become extinct. This is not necessarily a bad thing.
Many creatures are extinct because they have become something else.
There have been several mass extinctions that have caused widespread endings to species. 65 MYA dinosaurs became extinct. Today Approximately 10 species per day go extinct because of human involvement. Mass extinctions may have been caused by environmental stresses.