Mass extinctions and land plant evolution.

Nearly all modern animal phyla emerged 'suddenly' during the early Cambrian Period about 518 million years ago (Ma) in an event known as the Cambrian explosion. Following this evolutionary milestone, the marine invertebrate fossil record is punctuated by five major mass extinction events, collectively called the 'Big Five'. These events include the end-Ordovician, Late Devonian, end-Permian, end-Triassic, and end-Cretaceous mass extinctions (Figure 1). Among them, the end-Permian extinction was the most catastrophic event, resulting in the loss of approximately 81% of marine species within a short geological interval. In this primer, I will discuss the potential reasons why the End-Permian extinction event had such a profound effect on terrestrial plant life. I will draw examples from the best preserved ecosystem from this time period - the Cathaysian Flora.