Complex marine bioturbation ecosystem engineering behaviors persisted in the wake of the end-Permian mass extinction

Alison T Cribb,David J Bottjer

doi:10.1038/s41598-019-56740-0

Abstract

The end-Permian mass extinction was the most severe mass extinction event of the Phanerozoic and was followed by a several million-year delay in benthic ecosystem recovery. While much work has been done to understand biotic recovery in both the body and trace fossil records of the Early Triassic, almost no focus has previously been given to analyzing patterns in ecosystem engineering complexity as a result of the extinction drivers. Bioturbation is a key ecosystem engineering behavior in marine environments, as it results in changes to resource flows and the physical environment. Thus, the trace fossil record can be used to examine the effect of the end-Permian mass extinction on bioturbating ecosystem engineers. We present a dataset compiled from previously published literature to analyze burrowing ecosystem engineering behaviors through the Permian-Triassic boundary. We report two key observations: first, that there is no loss in bioturbation ecosystem engineering behaviors after the mass extinction, and second, that these persisting behaviors include deep tier, high-impact, complex ecosystem engineering. These findings suggest that while environmental conditions may have limited deeper burrowing, complex ecosystem engineering behaviors were able to persist in the Early Triassic. Furthermore, the persistence of deep tier bioirrigated three-dimensional network burrows implies that benthic biogeochemical cycling could have been maintained at pre-extinction states in some local environments, stimulating ecosystem productivity and promoting biotic recovery in the Early Triassic.

Highlights

The end-Permian mass extinction is recognized as the most devastating mass extinction event of the Phanerozoic, resulting in an estimated loss of 81% of all marine species[1] and a turnover of the Paleozoic evolutionary fauna to the Modern evolutionary fauna[2]
The transition layer has a lower water content, as it represents the beginning of compaction, which allows for the preservation of identifiable trace fossils
Tiering is a fundamental part of the ecosystem engineering analyses used in this research, and trace fossils without a precise description of penetration depth or tiering cannot be accurately analyzed in terms of ecosystem engineering behavior and the effect it may have had on the benthic environment

Summary

Introduction

The end-Permian mass extinction is recognized as the most devastating mass extinction event of the Phanerozoic, resulting in an estimated loss of 81% of all marine species[1] and a turnover of the Paleozoic evolutionary fauna to the Modern evolutionary fauna[2]. Bioturbation is the major allogenic ecosystem engineering behavior[14] due to the resulting alteration of substrate rheology[15], the mixing and redistribution of nutrients and sediments[16,17], the shift in sediment redox gradients[16,18], the creation of new habitats[17], and the construction of new ecospace[19]. The persistence or disappearance of these high-impact ecosystem engineering burrowing behaviors across the end-Permian mass extinction is key to understanding how marine ecosystems recovered in the Early Triassic.

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