Flume experiments reveal flows in the Burgess Shale can sample and transport organisms across substantial distances

Orla G Bath Enright,Nicholas J Minter,Luis A Buatois,M Gabriela Mángano,Esther J Sumner

doi:10.1038/s43247-021-00176-w

Abstract

The exceptionally preserved fossils entombed in the deposits of sediment-gravity flows in the Cambrian Burgess Shale of British Columbia have been fundamental for understanding the origin of major animal groups during the Cambrian explosion. More recently, they have been used to investigate the evolution of community structure; however, this assumes that the fossil assemblage represents an in-life community. Here we test this assumption for the first time based on experimental and field approaches. We use flume experiments to create analog flows and show that transport of the polychaete Alitta virens over tens of kilometers does not induce significantly more damage beyond that already experienced due to normal decay processes. Integration of experimental results with taphonomic assessment of fossils and sedimentological analysis suggests that the organisms of the Burgess Shale in the classic Walcott Quarry locality could have undergone substantial transport and may represent a conflation of more than one community.

Highlights

The exceptionally preserved fossils entombed in the deposits of sediment-gravity flows in the Cambrian Burgess Shale of British Columbia have been fundamental for understanding the origin of major animal groups during the Cambrian explosion
The above sedimentary features indicate transitional cohesive flows; quasi-laminar to upper transitional plug flows[22] that exhibit both turbulent and laminar characteristics and are capable of producing all of the features observed in the Burgess Shale deposits at the Walcott Quarry
Our results demonstrate that polychaetes of the Burgess Shale biota could potentially have been transported over substantial distances of at least 20 km

Summary

Introduction

The exceptionally preserved fossils entombed in the deposits of sediment-gravity flows in the Cambrian Burgess Shale of British Columbia have been fundamental for understanding the origin of major animal groups during the Cambrian explosion They have been used to investigate the evolution of community structure; this assumes that the fossil assemblage represents an in-life community. It is predicted that 30% of modern marine megafauna[2] and 80% of macrofauna genera[3] would leave no fossil record, whilst 86% of genera from the Burgess Shale would not have been preserved under normal circumstances[4] This has led to Burgess Shale-type lagerstätten being viewed as near-faithful representations of in-life communities and, as such, they have been used to reconstruct Cambrian marine community structure[4,5,6] and food-webs[7]. Whitney comparisons between transported treatments and nontransported controls reveal no significant difference in degradation (Supplementary Table 1)

Methods

Results

Conclusion