A three-dimensionally preserved lobopodian from the Herefordshire (Silurian) Lagerstätte, UK.

Derek J Siveter,Derek E G Briggs,Mark D Sutton,David J Siveter,David Legg

doi:10.1098/rsos.172101

Abstract

The Herefordshire (Silurian) Lagerstätte (approx. 430 Myr BP) has yielded, among many exceptionally preserved invertebrates, a wide range of new genera belonging to crown-group Panarthropoda. Here, we increase this panarthropod diversity with the lobopodian Thanahita distos, a new total-group panarthropod genus and species. This new lobopodian preserves at least nine paired, long, slender appendages, the anterior two in the head region and the posterior seven representing trunk lobopods. The body ends in a short post-appendicular extension. Some of the trunk lobopods bear two claws, others a single claw. The body is covered by paired, tuft-like papillae. Thanahita distos joins only seven other known three-dimensionally preserved lobopodian or onychophoran (velvet worm) fossil specimens and is the first lobopodian to be formally described from the Silurian. Phylogenetic analysis recovered it, together with all described Hallucigenia species, in a sister-clade to crown-group panarthropods. Its placement in a redefined Hallucigeniidae, an iconic Cambrian clade, indicates the survival of this clade to Silurian times.

Highlights

The Herefordshire Lagerstätte from the Welsh Borderland, UK is remarkable in preserving the soft part morphology2018 The Authors
Two lobopodians are known from the Carboniferous Mazon Creek Fauna of Illinois, Carbotubulus waloszeki and Helenodora inopinata [16,17] (Ilyodora divisa and Ilyodora elongata from Mazon Creek are regarded as nomina dubia [17,18])
[26] Diagnosis: Lobopodian panarthropods with ovoid head; a neck region bearing two or three pairs of nonannulated tentacle-like limbs that are thinner than the trunk lobopods; a trunk region bearing seven or eight long, tubular, smooth trunk lobopods, variously with either one or two claws; a short post- 4 appendicular region that is less than half as long as the distance between the last two lobopod pairs or is absent; body bearing dorso-lateral pairs of spinose projections or papillae. (Revised from Caron & Aria [8]; see below, Discussion, systematics.)

Summary

Introduction

The Herefordshire Lagerstätte from the Welsh Borderland, UK is remarkable in preserving the soft part morphology. Lobopodians are rare in the fossil record except in the Cambrian, which has yielded 20 or more species An undescribed animal from the mid-Silurian (upper Llandovery/lower Wenlock series) Waukesha biota, Wisconsin, USA was initially reported as a ‘myriapod-like animal’ [12,13], but later regarded as closer to the lobopodians or stem-group arthropods [14]. Undescribed form is known from the Silurian Eramosa Lagerstätte, Ontario, Canada [15]. Two lobopodians are known from the Carboniferous Mazon Creek Fauna of Illinois, Carbotubulus waloszeki and Helenodora inopinata [16,17] (Ilyodora divisa and Ilyodora elongata from Mazon Creek are regarded as nomina dubia [17,18]). All come from amber, with T. dominicanus and S. balticus each being known from a single specimen and C. burmiticus from four specimens

Material and methods

Systematic palaeontology

Systematics