Enduring evolutionary embellishment of cloudinids in the Cambrian.

Tae-Yoon S Park,Yong Yi Zhen,Jikhan Jung,Nigel C Hughes,Sangmin Lee,Lucas V Warren,Mirinae Lee,Hong Hua

doi:10.1098/rsos.210829

Abstract

The Ediacaran–Cambrian transition and the following Cambrian Explosion are among the most fundamental events in the evolutionary history of animals. Understanding these events is enhanced when phylogenetic linkages can be established among animal fossils across this interval and their trait evolution monitored. Doing this is challenging because the fossil record of animal lineages that span this transition is sparse, preserved morphologies generally simple and lifestyles in the Ediacaran and Cambrian commonly quite different. Here, we identify derived characters linking some members of an enigmatic animal group, the cloudinids, which first appeared in the Late Ediacaran, to animals with cnidarian affinity from the Cambrian Series 2 and the Miaolingian. Accordingly, we present the first case of an animal lineage represented in the Ediacaran that endured and diversified successfully throughout the Cambrian Explosion by embellishing its overall robustness and structural complexity. Among other features, dichotomous branching, present in some early cloudinids, compares closely with a cnidarian asexual reproduction mode. Tracking this morphological change from Late Ediacaran to the Miaolingian provides a unique glimpse into how a primeval animal group responded during the Cambrian Explosion.

Highlights

Biotic replacement during the Ediacaran–Cambrian transition separated the Proterozoic and Phanerozoic faunas, and represents one of the most remarkable evolutionary events in the history of life [1]
While soft-bodied evidence is required for precise determination, both interpretations affirm the cnidarian affinity for this group
The striking morphological similarity between the CLT clade and cloudinids evince a cnidarian affinity of cloudinids [6,17]

Summary

Introduction

Biotic replacement during the Ediacaran–Cambrian transition separated the Proterozoic and Phanerozoic faunas, and represents one of the most remarkable evolutionary events in the history of life [1] It was followed by the Cambrian Explosion, during which the fossil record of various extant animal phyla began to appear, along with the Earth’s first complex ecosystem engineering [2]. Establishing phylogenetic linkage across this interval can help illuminate the sequence of innovations that occurred across it and has considerable implications Securing such links is challenging for several reasons. The earliest biomineralized animals occurred in the terminal Ediacaran and had tubular construction in general Understanding their affinities, is challenging because of the relative morphological simplicity of these primeval structures, which are complicated by the apparent similarity shown by more derived metazoans. Recent researches have used these and other features to link the latest Ediacaran organisms to particular triplobastic groups [7,8]

Methods

Results

Conclusion