The youngest trigonotarbidPermotarbus schubertin. gen., n. sp. from the Permian Petrified Forest of Chemnitz in Germany

Jason A Dunlop,Ronny Rößler

doi:10.1002/mmng.201300012

Abstract

A new trigonotarbid (Arachnida: Trigonotarbida) is described as Permotarbus schuberti n. gen., n. sp. from the Early Permian Petrified Forest (Rotliegend) of Chemnitz in Saxony (Germany). At ca. 290 Ma it represents the youngest record of this extinct arachnid order discovered to date. Its familial affinities are uncertain, but may lie close to the Aphantomartidae. The distribution of the trigonotarbid genera through time is summarised, together with a list of their seventy-seven fossil-yielding localities. Together they offer a broad overview of the group's fossil record, which is heavily biased towards the Moscovian Stage (ca. 307â312 Ma) of the Late Carboniferous in Europe and North America. This is due in no small part to numerous localities associated with coal mining districts, and trigonotarbids are found less frequently after this stage. While it is tempting to associate this with biological events â such as a putative "Carboniferous Rainforest Collapse" dating to ca. 305 Ma â it is difficult to differentiate the effects of genuine extinction patterns from artefacts caused by fewer appropriate localities in the economically less relevant latest Carboniferous and Early Permian strata. Nevertheless, trigonotarbids became extinct at some point after the Early Permian and loss of the Coal Measures forests remains one of the most likely possible causes. doi:10.1002/mmng.201300012

Highlights

Trigonotarbids are an extinct order of arachnids with an essentially spider-like appearance, albeit characterised by an opisthosoma in which the dorsal tergites are divided into median and lateral plates; a feature which they share with the rare order Ricinulei
The distribution of the trigonotarbid genera through time is summarised, together with a list of their seventy-seven fossil-yielding localities. Together they offer a broad overview of the group’s fossil record, which is heavily biased towards the Moscovian Stage of the Late Carboniferous in Europe and North America
While it is tempting to associate this with biological events – such as a putative ‘Carboniferous Rainforest Collapse’ dating to ca. 305 Ma – it is difficult to differentiate the effects of genuine extinction patterns from artefacts caused by fewer appropriate localities in the economically less relevant latest Carboniferous and Early Permian strata

Summary

Introduction

Trigonotarbids are an extinct order of arachnids with an essentially spider-like appearance, albeit characterised by an opisthosoma in which the dorsal tergites are divided into median and lateral plates; a feature which they share with the rare order Ricinulei. They are presently restricted to the Carboniferous–Permian boundary of Bajo de Vliz in Argentina (Pinto & Hçnicken 1980), and a number of localities in the Rotliegend of Thuringia in eastern Germany (Scharf 1924; Mçller 1957; Ræßler 1998; Ræßler et al 2003) These German records date to about 295 Ma (Asselian) based on biostratigraphic considerations (Schneider & Werneburg 2006); precise geochronological ages are presently lacking. In the broader context of trigonotarbid geological history, we document visually (Fig. 5) the stratigraphic ranges of the known genera and list localities by age which have yielded fossils of these arachnids (Table 1) We discuss whether this is part of a genuine loss of diversity – part of a shift towards the eventual extinction of the Trigonotarbida – or an artefact of less accessible and/or less intensively mined rock sequences suitable for their preservation

Materials and methods

Discussion