Late Ordovician and early Silurian trilobites from Tasmania

Abstract

Thirteen species of trilobites are described from two different faunas in late Katian and Rhuddanian strata respectively of the Arndell Sandstone in the Florentine Valley of southern Tasmania. The late Katian fauna includes the trinucleid Auritolithus corbetti gen. et sp. nov., the calymenids Salterocoryphe ? bailliei sp. nov. and Vietnamia hyron sp. nov., and limited material of the lichid Amphilichas ? and two indeterminate asaphids. Auritolithus , characterized by the markedly subpentagonal outline of the cephalon, cannot be assigned to any of the existing trinucleid subfamilies but seems closely related to forms occurring in the Upper Ordovician of the Precordillera Basin of Argentina. Salterocoryphe ? bailliei , the first record of a member of the Colpocoryphinae from Australia, is considerably younger stratigraphically than other occurrences of that genus in the middle to upper Darriwilian of France and the Iberian Peninsula. The Rhuddanian fauna from the Arndell Sandstone includes the illaenid Pepodes agrestis gen. et sp. nov., the scutelluid Japonoscutellum senectum sp. nov., the brachymetopid Niuchangella agastor sp. nov., the encrinurids Arndellaspis oryxis gen. et sp. nov. and Cromus ?, the calymenid Gravicalymene clarkei sp. nov. and the homalonotid Brongniartella calveri sp. nov. Niuchangella is accepted as a senior synonym of Radnoria . Arndellaspis is not closely related to other members of the Encrinurinae from Australia but shares unique derived characters of the pygidium with Encrinurus ( s.s. ) and Wallacia , occurring in Laurentia, Avalonia and Baltica, and Arndellaspis may share common ancestry with Encrinurus . The commonly broadly interpreted Gravicalymene is revised and restricted to a smaller number of closely related species from the Darriwilian to middle Telychian. The faunal affinities of the trilobites suggest links with terranes that lay along the north-western margin of Gondwana and with South America in the Late Ordovician, and with South China and possibly Laurentia in the early Silurian.