180 million years ago, the supercontinent Pangaea broke up into several landmasses to form the face of the Earth as we know it today.
Northern Pangaea, called Laurasia, separated from the south, Gondwana. Laurasia became North America and Eurasia. Gondwana would become Africa, South America, India and Antarctica/Australia. The North Atlantic Ocean would start to form between Laurasia and Gondwana. Antarctica and Australia separated from Gondwana, moving south and becoming different immense islands. The South Atlantic Ocean appeared between South America and Africa while India broke away and began its journey heading north to collide with Asia and produce the Himalayas.
Many species which had inhabited contiguous territories became physically isolated. It is the reason why today fossils of the same species appear in distant regions. It is the same reason why there are distinct species in one area, such as marsupials in Australia. These species evolved entirely isolated from the rest of the animals on the planet.
All these continental movements induced climate change. The emergence of mountains produces cold regions. The existence of continents at the poles causes the formation of glaciers which lowers the sea level. More coastlines mean more shallow-water areas for sea creatures to benefit from.
Life evolved in the major continental masses subject to fierce competition, as opposed to what happened in the islands, where evolution works in isolation and with much fewer resources.