Contrasting Early Ordovician assembly patterns highlight the complex initial stages of the Ordovician Radiation

Farid Saleh,Allison C Daley,Luis A Buatois,M Gabriela Mángano,Bertrand Lefebvre,Fernanda Serra,Daniel Vizcaïno,Corentin Gibert,Diego Balseiro,Beatriz G Waisfeld,Jonathan B Antcliffe,Pauline Guenser,Xiaoya Ma

doi:10.1038/s41598-022-07822-z

Abstract

The Early Ordovician is a key interval for our understanding of the evolution of life on Earth as it lays at the transition between the Cambrian Explosion and the Ordovician Radiation and because the fossil record of the late Cambrian is scarce. In this study, assembly processes of Early Ordovician trilobite and echinoderm communities from the Central Anti-Atlas (Morocco), the Montagne Noire (France), and the Cordillera Oriental (Argentina) are explored. The results show that dispersal increased diachronically in trilobite communities during the Early Ordovician. Dispersal did not increase for echinoderms. Dispersal was most probably proximally triggered by the planktic revolution, the fall in seawater temperatures, changes in oceanic circulation, with an overall control by tectonic frameworks and phylogenetic constraints. The diachronous increase in dispersal within trilobite communities in the Early Ordovician highlights the complexity of ecosystem structuring during the early stages of the Ordovician Radiation. As Early Ordovician regional dispersal was followed by well-documented continental dispersal in the Middle/Late Ordovician, it is possible to consider that alongside a global increase in taxonomic richness, the Ordovician Radiation is also characterized by a gradual increase in dispersal.

Highlights

The Early Ordovician is a key interval for our understanding of the evolution of life on Earth as it lays at the transition between the Cambrian Explosion and the Ordovician Radiation and because the fossil record of the late Cambrian is scarce
Trilobites in the Montagne Noire (MN) are dispersal-assembled in the Tremadocian and the Floian (i.e., Dispersal and Niche Continuum index (DNCI) is negative and does not overlap with zero; Fig. 4b)
Dispersal increase was not homogenous for all animal groups and regions (Fig. 4b) as it was controlled by a combination of clade inherent features and the tectonic framework of each region

Summary

Introduction

The Early Ordovician is a key interval for our understanding of the evolution of life on Earth as it lays at the transition between the Cambrian Explosion and the Ordovician Radiation and because the fossil record of the late Cambrian is scarce. Assembly processes of Early Ordovician trilobite and echinoderm communities from the Central Anti-Atlas (Morocco), the Montagne Noire (France), and the Cordillera Oriental (Argentina) are explored. The results show that dispersal increased diachronically in trilobite communities during the Early Ordovician. This work investigates the ecological processes that structure community composition during the Early Ordovician of three regions: The Central Anti-Atlas (CAA; Morocco), Montagne Noire (MN; France), and Cordillera. Once seen as incompatible hypotheses, niche- and dispersal-perspectives are seen as opposite ends of a c ontinuum[24–26] Within this continuum, the taxonomic composition of an assemblage may result to a greater or lesser extent of each process, or from an equal combination of the two[24–26]

Methods

Results

Conclusion