An early Pangaean vicariance model for synapsid evolution

Leonidas Brikiatis

doi:10.1038/s41598-020-70117-8

Abstract

Genetic isolation due to geographic separation (vicariance) is the best understood cause of vertebrate speciation. Nevertheless, it has never been demonstrated in the fossil record across a wide range of taxa. Here, by reviewing in-depth the available data of the Late Palaeozoic (~ 350–250 million years ago), I reconstructed an early Pangaean junction-disjunction palaeogeographic model and showed that it coincides strongly with time-calibrated cladograms of the Late Palaeozoic synapsids (the primitive ancestors of modern mammals). The temporal development of the vicariant topology seems to fit closely with the emergence rhythm of the recovered synapsid taxa, suggesting vicariance due to Pangaean separation as the cause of early amniote evolution. The inferred vicariant topology also accounts for the observed pattern in the North American marine biostratigraphic units. Accordingly, the model demonstrates the link between the evolution of life on Earth and palaeogeographic evolution and strongly supports allopatric speciation through vicariance as the prominent mode of amniote evolution. Furthermore, correlations between state-of-the-art biochronostratigraphic charts and this palaeogeographic model suggest that the arido-eustasy model can explain the mid-Permian biotic extinction event and depositional cycles, such as the pre-Zechstein of the Central European Basin.

Highlights

Genetic isolation due to geographic separation is the best understood cause of vertebrate speciation
Based on the most apparent episodes of sea-level change that affected the southern connections between the Uralian Seaway (URS) and the Palaeotethys, an early Pangaean junction-disjunction palaeogeographic model was reconstructed and compared to time-calibrated consensus cladograms (“clado-stratigraphic patterns”) of Late Palaeozoic vertebrates to determine whether a vicariance pattern can explain early synapsid evolution
Given the wide terrestrial connection between the URS and rest of Pangaea, exposure to the Siberian Land Bridge (SLB) and the associated sea-level fluctuations[16] were the only factors contributing to the vicariance pattern in the Pangaean junction-disjunction model (Fig. 1)

Summary

Introduction

Genetic isolation due to geographic separation (vicariance) is the best understood cause of vertebrate speciation It has never been demonstrated in the fossil record across a wide range of taxa. Vicariance is the best understood mode of s peciation[1,2], due to the absence of detailed scenarios of palaeogeographic changes and sufficiently resolved and representative phylogenetic trees, allopatric speciation has not been confirmed for a wide range of taxa in the vertebrate fossil record. Based on the most apparent episodes of sea-level change that affected the southern connections between the Uralian Seaway (URS) and the Palaeotethys, an early Pangaean junction-disjunction palaeogeographic model was reconstructed and compared to time-calibrated consensus cladograms (“clado-stratigraphic patterns”) of Late Palaeozoic vertebrates to determine whether a vicariance pattern can explain early synapsid evolution

Objectives

Methods

Results

Discussion

Conclusion