Were the First Trace Fossils Really Burrows or Could They Have Been Made by Sediment-Displacive Chemosymbiotic Organisms?

Duncan Mcilroy

doi:10.3390/life12020136

Abstract

This review asks some hard questions about what the enigmatic graphoglyptid trace fossils are, documents some of their early fossil record from the Ediacaran–Cambrian transition and explores the idea that they may not have been fossils at all. Most researchers have considered the Graphoglyptida to have had a microbial-farming mode of life similar to that proposed for the fractal Ediacaran Rangeomorpha. This begs the question “What are the Graphoglyptida if not the Rangeomorpha persevering” and if so then “What if…?”. This provocative idea has at its roots some fundamental questions about how to distinguish burrows sensu-stricto from the external molds of endobenthic sediment displacive organisms.

Highlights

Trace Fossils Really Burrows orThe importance of the first colonization of the sedimentary realm by infaunal organisms has been at the heart of discussions around the evolution of complex animal life and the beginning of the Cambrian Explosion of animal life [1,2,3,4]
The base of the Cambrian period is defined by the first occurrence of trace fossils belonging to the Treptichnus pedum Assemblage Zone [5,6] at a point in rock in Fortune Head in Newfoundland, Canada approx
The record of the end of the Ediacaran and the Cambrian explosion of animal life includes examples of Ediacaran survivors in Cambrian rocks (e.g., Swarpuntia [33,34]), and evidence of putative Cambrian type trace fossils below the recognized Ediacaran Cambrian boundary [35,36,37]. It is to this latter transition, from the matground dominated Ediacaran to the macroscopically bioturbated Cambrian [2,38] that our attention is drawn

Summary

Introduction

The importance of the first colonization of the sedimentary realm by infaunal organisms has been at the heart of discussions around the evolution of complex animal life and the beginning of the Cambrian Explosion of animal life [1,2,3,4]. The record of the end of the Ediacaran and the Cambrian explosion of animal life includes examples of Ediacaran survivors in Cambrian rocks (e.g., Swarpuntia [33,34]), and evidence of putative Cambrian type trace fossils below the recognized Ediacaran Cambrian boundary [35,36,37]. It is to this latter transition, from the matground dominated Ediacaran to the macroscopically bioturbated Cambrian [2,38] that our attention is drawn

Microbially Dominated Seafloors at the Dawn of Animal Life

The Slow Death of the Ediacaran-Type Matground Biotope

The Early Putative Burrowers of the Ediacaran–Cambrian Transition

What are the Graphoglyptida if not the Rangeomorpha Persevering?

The Tree-Like Graphoglyptids of the E-C Boundary

The Net-Like Graphoglyptida