Heterogeneous and dynamic marine shelf oxygenation and coupled early animal evolution.

It is generally agreed that early diversification of animals and significant rise of atmospheric and oceanic oxygen (O2) levels occurred in the Ediacaran (635-541 million years ago, Ma) and early Cambrian (ca. 541-509 Ma). The strength and nature of their relationship, however, remain unclear and debated. A recent wave of paleoredox research - with a particular focus on the fossiliferous sections in South China - demonstrates high spatial heterogeneity of oceanic O2 (redox) conditions and dynamic marine shelf oxygenation in a dominantly anoxic ocean during the Ediacaran and early Cambrian. This pattern shows a general spatiotemporal coupling to early animal evolution. We attribute dynamic shelf oxygenation to a complex interplay among the evolving atmosphere, continents, oceans, and biosphere during a critical period in Earth history. Our review supports the idea of a complex coevolution between increasing O2 levels and early diversification of animals, although additional work is required to fully delineate the timing and patterns of this coevolution and the mechanistic underpinnings.