A novel tool to untangle the ecology and fossil preservation knot in exceptionally preserved biotas

Farid Saleh,Orla G Bath-Enright,Allison C Daley,Bertrand Lefebvre,Bernard Pittet,Antoine Vite,Xiaoya Ma,M Gabriela Mángano,Luis A Buatois,Jonathan B Antcliffe

doi:10.1016/j.epsl.2021.117061

Abstract

Understanding the functioning of extinct ecosystems is a complicated knot of ecological, evolutionary, and preservational strands that must be untangled. For instance, anatomical and behavioral differences can profoundly alter fossilization pathways. This is particularly true in exceptionally preserved soft-bodied biotas that record the earliest phases of animal evolution during the Cambrian Explosion and the Ordovician Radiation. Herein, a novel method of data partitioning based on probabilistic modelling is developed to examine these processes for the Walcott Quarry, Burgess Shale, Canada (510Ma), and the Fezouata Shale, Morocco (c. 475Ma). The modelling shows that the mechanism for soft-tissue preservation in the Walcott Quarry is ecologically selective, favoring the endobenthos. This is not found in the Fezouata Shale. Taken in concert with bioturbation data, a new model of comparative preservation is developed based on sedimentary flow dynamics. This suggests that during the Cambrian Explosion and Ordovician Radiation the most exceptional fossils sites must still be calibrated against each other to understand the unfolding evolutionary events and the ecological structuring of ancient animal communities.

Highlights

Animal communities from the Cambrian and the Ordovician are some of the most complete in the fossil record, with exceptional fossilization of soft tissues giving a comprehensive view of faunal diversity during the Cambrian Explosion and the OrdovicianRadiation
The data matrices for the generic composition and biological tissue occurrences [i.e., biominerals (A) such as brachiopod shells, sclerites (B) such as the headshield of some arthropods, cuticle formed of polysaccharides (C) such as the body walls of priapulids, cellular body walls (D) as in cambroernids, and internal organs (E) such as digestive and nervous systems] in the Walcott Quarry and the Fezouata Shale were taken from a previously published database (Saleh et al, 2020b) based on the collections of the University of Lyon (France), the University of Marrakech (Morocco), and the University of Lausanne (Switzerland), the Royal Ontario Museum (Canada), and the Peabody Museum (USA)
In the Walcott Quarry, there are generally more tissues preserved per taxon than in the Fezouata Shale, and these values show more variation between the three modes of life (Fig. 1b)

Summary

Introduction

Animal communities from the Cambrian and the Ordovician are some of the most complete in the fossil record, with exceptional fossilization of soft tissues giving a comprehensive view of faunal diversity during the Cambrian Explosion and the OrdovicianRadiation. Animal communities from the Cambrian and the Ordovician are some of the most complete in the fossil record, with exceptional fossilization of soft tissues giving a comprehensive view of faunal diversity during the Cambrian Explosion and the Ordovician. The Walcott Quarry (Miaolingian, Wuliuan, Cambrian, Burgess Shale, Canada) bears a diverse assemblage of soft-bodied animals preserved in minute details (Nanglu et al., 2020). The Fezouata Shale offers a more complete view of the transition between the Cambrian Explosion and the Ordovician Radiation than was previously known (Van Roy et al, 2010). Mode of preservation defined by carbonaceous compressions (Gaines et al, 2008; Saleh et al., 2020a). Preservation was aided by rapid sediment influx (Gaines, 2014)

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Discussion

Conclusion