A new probable stem lineage crustacean with three-dimensionally preserved soft parts from the Herefordshire (Silurian) Lagerstätte, UK

Abstract

A new arthropod with three-dimensionally preserved soft parts, Tanazios dokeron, is described from the Wenlock Series (Silurian) of Herefordshire, England, UK. Serial grinding, digital photographic and computer rendering techniques yielded 'virtual fossils' in the round for study. The body tagmata of T. dokeron comprise a head shield and a long trunk. The head shield bears six pairs of horn-like spines and the head bears five pairs of appendages. The antennule, antenna and mandible are all uniramous, and the mandible includes a gnathobasic coxa. Appendages four and five are biramous and similar to those of the trunk: each comprises a limb base with an endite, an enditic membrane, and two epipodites, plus an endopod and exopod. The hypostome bears a large cone-like projection centrally, and there may be a short labrum. The trunk has some 64 segments and at least 60 appendage pairs. A very small telson has the anus sited ventrally in its posterior part and also bears a caudal furca. Comparative morphological and cladistic analyses of T. dokeron indicate a crustacean affinity, with a probable position in the eucrustacean stem group. As such the epipodites in T. dokeron are the first recorded in a eucrustacean stem taxon. The new species is interpreted as a benthic or nektobenthic scavenger.

Waptia revisited: Intimations of behaviors

“…1 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 Claiming the loss of an ancestral structure, in this instance the second pair of postocular appendages, can be contentious simply because proving loss is only possible from developmental studies of extant species, such as the transient expression of the appendicular marker gene distalless (Williams and Nagy, 1996). However, as discussed by Boxshall (2007) in contesting the interpretation of the Silurian arthropod Tanazios dokeron (Siveter et al, 2007) as possessing antennules and antennae, evidence for the evolved loss of antennae in Tanazios is indicated, amongst other features, by a prominent gap containing ventrolateral bulges each side of the hypostome between the antennules and the mandibles. The present examples of Waptia mouthparts come from specimens that have suffered distortion during entombment, so that distances between antennules and first gnathal appendages cannot be properly estimated nor can lateral bulges (or hypostome) yet be identified.…”

An exceptionally preserved myodocopid ostracod from the Silurian of Herefordshire, UK

“…The fossils preserve extraordinary detail of soft parts and furnish remarkable palaeobiological and evolutionary data. They include a polychaete worm (Sutton et al 2001c), an aplacophoran-like mollusc (Sutton et al 2001a(Sutton et al ,b, 2004, a gastropod (Sutton et al 2006), a pycnogonid ), a stem-group chelicerate (Orr et al 2000b;Sutton et al 2002), a marrellomorph (Siveter et al 2007b), a stem-group crustacean (Siveter et al 2007c), ostracods (Siveter et al , 2007a, a barnacle (Briggs et al 2005), a phyllocarid ), a brachiopod (Sutton et al 2005a), a stem-group asteroid (Sutton et al 2005b) and a large variety of unpublished forms.…”

Simple 3D images from fossil and Recent micromaterial using light microscopy

“…The method in general enables the production of stereo images from a transmitted light microscope (Figs 2A, 3A and 4). Stereo images have already proven to be a powerful documenting tool with other methods (Kallenborn et al , 1990; Purnell 2003; Gatesy et al , 2005; Siveter et al , 2007a, b, and references therein). The method is completely non‐destructive and does not need preparations of the specimens and can thus be applied to type material (Scott et al , 2000).…”

“…Since the method has been established, an impressive range of taxa has been described from the Herefordshire Lagerstätte using this particular reconstructive method. The taxonomic range spans from different arthropods over trochozoans and tentaculates to echinoderms (Siveter et al , 2007a, b, and references therein). The common principle of most of these methods for reconstructing 3D information from an image stack is usually referred to as a multi‐planar reconstruction.…”

“…Although this method does not give the possibility of viewing the specimen of interest from several angles, it yields additional information compared to usual 2D images (Gatesy et al , 2005) and can be combined with other 3D documenting methods (e.g. Müller, 1983; Walossek, 1993; Knappertsbusch et al , 2006; Siveter et al , 2007a, b, and references therein).…”