Recovery of ecosystems

Each extinction event has dire consequences for life on Earth but it also creates opportunity for new radiations and diversifications. In the previous week, we stressed the enormous impact of the End Permian extinction event that destroyed so much of life at the time. Recovery of ecosystems post-extinction was slow – taking longer on land than in oceans. It is estimated to have taken about 8 million years for ecosystems to re-establish in the marine realms, but on land, it is estimated to have taken about 10-20 million years for complex ecosystems to revive!

During the Permian, cynodonts (a kind of therapsid) were quite sparse, but they survive the extinction event, and experience a significant adaptive radiation thereafter, and eventually give rise to mammals. The top predators of the Triassic were taken by archosaurs – which give rise to two fearsome lineages – the crocodilians and the better-known, dinosaurs, who became dominant in the latter part of the Triassic. Remnants of these lineages are present among modern animals – but we will talk more about that later this week.

Some major events in the history of life on earth chart

The fossil record tells us that the long recovery after the End Permian started to show increasing diversity in the late Triassic period – but it is also around then the fourth extinction struck (about 208 mya). On land, large animals were most affected, as well as an estimated 64% of marine reptiles. Plant life did not suffer many extinctions this time. Although scientists have some evidence to work from, there are several theories about the causes of the End Triassic extinction event. In the next step, I have summarised some of the key ideas about what happened.