Echinoids from the Tesero Member (Werfen Formation) of the Dolomites (Italy): implications for extinction and survival of echinoids in the aftermath of the end-Permian mass extinction.

Jeffrey R Thompson,Renato Posenato,Elizabeth Petsios,David J Bottjer

doi:10.7717/peerj.7361

Jeffrey R Thompson, Renato Posenato + Show 2 more

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https://doi.org/10.7717/peerj.7361

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Abstract

The end-Permian mass extinction (∼252 Ma) was responsible for high rates of extinction and evolutionary bottlenecks in a number of animal groups. Echinoids, or sea urchins, were no exception, and the Permian to Triassic represents one of the most significant intervals of time in their macroevolutionary history. The extinction event was responsible for significant turnover, with the Permian–Triassic representing the transition from stem group echinoid-dominated faunas in the Palaeozoic to Mesozoic faunas dominated by crown group echinoids. This turnover is well-known, however, the environmental and taxonomic distribution of echinoids during the latest Permian and Early Triassic is not. Here we report on an echinoid fauna from the Tesero Member, Werfen Formation (latest Permian to Early Triassic) of the Dolomites (northern Italy). The fauna is largely known from disarticulated ossicles, but consists of both stem group taxa, and a new species of crown group echinoid, Eotiaris teseroensis n. sp. That these stem group echinoids were present in the Tesero Member indicates that stem group echinoids did not go extinct in the Dolomites coincident with the onset of extinction, further supporting other recent work indicating that stem group echinoids survived the end-Permian extinction. Furthermore, the presence of Eotiaris across a number of differing palaeoenvironments in the Early Triassic may have had implications for the survival of cidaroid echinoids during the extinction event.

Highlights

The end-Permian extinction saw the demise of several evolutionary lineages, and ushered in the taxonomic and ecological restructuring of marine invertebrate ecosystems that gave rise to the Modern Fauna (Sepkoski, 1984)
In addition to the specimen of Eotiaris, we describe additional disarticulated material from the Tesero Member which is attributed to both stem group and crown group echinoids
CNT10 contains a fauna dominated by the brachiopod Orbicoelia (=?Crurithyris of Broglio Loriga et al, 1988), while CNT11 is dominated by Teserina nerii (Posenato, 2011)

Summary

Introduction

The end-Permian extinction saw the demise of several evolutionary lineages, and ushered in the taxonomic and ecological restructuring of marine invertebrate ecosystems that gave rise to the Modern Fauna (Sepkoski, 1984). The end-Permian mass extinction represents one of the most significant intervals of time for understanding the macroevolutionary history of echinoids (Erwin, 1993; Erwin, 1994; Benton, 2003; Thompson et al, 2018). Almost all of the postPalaeozoic echinoids, have a body plan constructed of only two columns of interambulacral and ambulacral plates (Erwin, 1993; Erwin, 1994; Kroh & Smith, 2010), indicating significant turnover during the Permian–Triassic interval. In the late Palaeozoic, echinoid faunas were comprised of the stem group families Archaeocidaridae, Lepidesthidae, Proterocidaridae, Cravenechinidae and Lepidocentridae (Jackson, 1912; Kier, 1958b; Kier, 1965; König, 1982; Thompson, Petsios & Bottjer, 2017) and the early crown group echinoids of the family Miocidaridae (Smith & Hollingworth, 1990; Thompson et al, 2015). Only one genus, the miocidarid Eotiaris, is known from fossil representatives on both sides of the mass extinction event (Smith & Hollingworth, 1990; Thompson et al, 2015; Godbold et al, 2017), though phylogenetic analyses indicate more boundary crossers likely existed as ghost lineages (Smith, 2007; Thompson et al, 2018; Pietsch et al, 2019)

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