Satunarcus, a new late Cambrian trilobite genus from southernmost Thailand and a reevaluation of the subfamily Mansuyiinae Hupé, 1955

Shelly J Wernette,Nigel C Hughes,Paul M Myrow,Apsorn Sardsud

doi:10.1017/jpa.2020.23

Shelly J Wernette, Nigel C Hughes + Show 2 more

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https://doi.org/10.1017/jpa.2020.23

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Abstract

AbstractThe Ao Mo Lae Formation of the Tarutao Group crops out on Thailand's Tarutao Island and contains a diverse assemblage of late Furongian trilobite taxa, including several endemic forms. This study presents a new genus and species, Satunarcus molaensis, discovered at two locations on the island. A cladistic analysis of the kaolishaniid subfamily Mansuyiinae in light of Satunarcus and similar genera known from across upper Cambrian equatorial Gondwanan rocks suggests that the subfamily is polyphyletic in its current definition, and thus is not a natural group. Separating Mansuyia Sun, 1924 from the other taxa conventionally placed in Mansuyiinae permits recognition of a previously unrecognized monophyletic subfamily Ceronocarinae new subfamily. As established herein, this kaolishaniid subfamily contains Satunarcus n. gen. and all genera previously recognized as Mansuyiinae. with the exception of Mansuyia itself. Ceronocarinae n. subfam. occur in middle Jiangshanian to middle Cambrian Stage 10 sedimentary rocks from Australia, South China, North China, and Sibumasu, with most genera endemic to Australia.UUID: http://zoobank.org/618c5136-73f0-4912-a7d3-e56559d2a76c

Highlights

Peninsular Thailand’s latest Cambrian strata comprise interbedded fossiliferous sandstones and rhyolitic ash beds, making this succession important for resolving the geochronology of the Cambro-Ordovician boundary (Stait et al, 1984)
Satunarcus n. gen. belongs to Kaolishaniidae (Kobayashi, 1935) and, while morphologically distinctive, bears close resemblance to genera known from Australia, North China, and South China
Cladistic analysis of Mansuyiinae, “Mansuyia-like” genera, and related members of Kaolishaniidae and Tsinaniidae reveals that Mansuyia and other genera assigned to Mansuyiinae (Shergold, 1972) are polyphyletic, the restriction of the subfamily Mansuyiinae to Mansuyia alone

Summary

Introduction

Peninsular Thailand’s latest Cambrian strata comprise interbedded fossiliferous sandstones and rhyolitic ash beds, making this succession important for resolving the geochronology of the Cambro-Ordovician boundary (Stait et al, 1984). Trilobites of the corynexochid suborder Leiostegiina, tsinaniids and kaolishaniids, are prevalent in the late Cambrian (Furongian) record from equatorial Gondwana They occur in Sibumasu, South and North China, Bhutan, and Australia (Sun, 1924; Shergold, 1972, 1975, 1991; Shergold et al, 1988; Zhu et al, 2010, 2013; Hughes et al, 2011; Park et al, 2014). The evolution and dispersal patterns of Kaolishaniidae Kobayashi (1935) and Tsnianiidae Kobayashi (1933) reflect Cambro-Ordovician paleogeography during the final accretion of Gondwana prior to its mid-Paleozoic breakup (Cawood et al, 2007) These trilobites are useful index taxa for establishing Stage 10 biozones, including the Shergoldia nomas Zone of Australia and the Ptychaspis-Tsinania and Kaolishania pustulosa Zones of North China (Geyer and Shergold, 2000). The discovery of a new kaolishaniid genus, Satunarcus, from Thailand’s Tarutao Group and its affinities with various genera traditionally classified as Mansuyiinae Hupé (1955) prompts a revision of this subfamily and its role in the evolution of Tsinaniidae from Kaolishaniidae

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