The importance of oxygen for the disparate recovery patterns of the benthic macrofauna in the Early Triassic

The end-Permian mass extinction, 252 million years ago, decimated life on Earth including the benthic marine invertebrate macrofauna. A return to pre-extinction levels of diversity and complex ecological systems took approximately 5 million years. This review provides the most up to date synthesis of the progression of the benthic marine invertebrate macrofaunal recovery. We found the rates and patterns of the benthic recovery to vary both across the globe and between different investigators. The continuation of deleterious environmental conditions including low oxygen concentrations and high temperatures likely played a large role in the delayed recovery. Ocean basins, such as Neo-Tethys, show evidence for continued oxygenation past the extinction event which extended the lifespan and diversity of specific benthic communities. Shortly after the extinction boundary, shoreface environments with moderate wave energy were sites of water column oxygenation that supported a more rapid return to diverse and ecologically complex benthic communities. We find that the location and longevity of oxygenated environments is an overarching mechanism that partially explains varied global recovery patterns. Synergistic perturbations including an acidification event at the Permian–Triassic boundary and high temperature events contributed to lasting environmental perturbations. In an effort to standardize future results and discussion of the benthic recovery, we support the use of a modified recovery rubric proposed here.