Most living species are result the of natural selection, BUT…
There is some strong examples of natural selection role, such as: 1- the dinosaurs extinction, any theory such as: 1a- Ice age or volcanism generating colder or warmer climates impossible to cope with dinosaurs physiology 1b- Asteroid impact(s): the darkness killed most of the cretaceous plants and then herbivorous dinosaurs starved, and subsequently their predators
2- The first vertebrates on earth coming from some Devonic fishes, the water they lived shrinked continuously (many theories, tides, desert effect, etc) giving the advatage to species able to catch atmospheric air with the presence of lungs and be able to move on earth, those fishes used their fins to move at the bottom of the water and the were also useful to move on the land. They were then privileged to survive in dry periods and then colonize a new environment rich in oxygen, plants and insects.
I hope this helps
