Abstract

The mass extinction characterizing the Permian/Triassic boundary (PTB; ~ 252 Ma) corresponds to a major faunal shift between the Palaeozoic and the Modern evolutionary fauna. The temporal, spatial, environmental, and ecological dynamics of the associated biotic recovery remain highly debated, partly due to the scarce, or poorly-known, Early Triassic fossil record. Recently, an exceptionally complex ecosystem dated from immediately after the Smithian/Spathian boundary (~ 3 myr after the PTB) was reported: the Paris Biota (Idaho, USA). However, the spatiotemporal representativeness of this unique assemblage remained questionable as it was hitherto only reported from a single site. Here we describe three new exceptionally diverse assemblages of the same age as the Paris Biota, and a fourth younger one. They are located in Idaho and Nevada, and are taxonomic subsets of the Paris Biota. We show that the latter covered a region-wide area and persisted at least partially throughout the Spathian. The presence of a well-established marine fauna such as the Paris Biota, as soon as the early Spathian, indicates that the post-PTB biotic recovery and the installation of complex ecosystems probably took place earlier than often assumed, at least at a regional scale.

Highlights

  • The mass extinction characterizing the Permian/Triassic boundary (PTB; ~ 252 Ma) corresponds to a major faunal shift between the Palaeozoic and the Modern evolutionary fauna

  • At the Permian/Triassic boundary (PTB; ~ 252 Ma), the most severe Phanerozoic mass extinction led to the disappearance of over 80% of marine ­genera[1,2]

  • Dated from immediately after the Smithian/Spathian boundary (SSB; ~ 249.2 ­Ma16), this biota provides a novel window on Early Triassic ecosystems

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Summary

Early Triassic ecosystems during the early Spathian

Beyond the Paris Canyon assemblage, these new sites even document the only known occurrences of such taxa in eastern Panthalassa for this time interval They cover a wide range of ecological guilds, and yield benthic, nektobenthic as well as nektonic organisms. The newly reported taxa are mostly bivalves, which is an over sampled clade in this assemblage compared to the Paris Biota It is likely after further sampling at both sites (NoName and Paris Canyon), their taxonomic composition will converge. Such low spatial turnover and high nestedness components indicate that the studied faunas are strongly related to the Paris Biota. The Paris Biota can no longer be regarded as a local transient exception, as these new sites provide evidence that (i) it was spatially extended, at least at a regional scale with a distribution greater than the northern part of the western USA basin; and (ii) it spanned at least partially, throughout the Spathian

Significance in the context of the Early Triassic recovery
Methods
Author contributions
Findings
Additional information

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