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

Abstract

An exceptionally preserved new ostracod crustacean from the Silurian of Herefordshire, UK, represents only the third fully documented Palaeozoic ostracod with soft-part preservation. Appendages, gills, gut system, lateral compound eyes and even a medial eye with a Bellonci organ are preserved, allowing assignment of the fossil to a new genus and species of cylindroleberidid myodocope (Myodocopida, Cylindroleberididae). The Bellonci organ is recorded for the first time in fossil ostracods. The find also represents a rare occurrence of gills in fossil ostracods and confirms the earliest direct evidence of a respiratory-cum-circulatory system in the group. The species demonstrates remarkably conserved morphology within myodocopes over a period of 425 Myr. Its shell morphology more closely resembles several families of myodocopes other than the Cylindroleberididae, especially the Cypridinidae and Sarsiellidae, thus questioning the utility of the carapace alone in establishing the affinity of fossil ostracods.

A Silurian myodocope with preserved soft-parts: cautioning the interpretation of the shell-based ostracod record

“…This confirms that carapace morphology alone is an inadequate basis for suprageneric assignment of (Recent) myodocopes [41]. The discovery of P. avibella with a soft-part morphology that is at odds with the appearance of the carapace encourages caution in interpreting the affinities of Palaeozoic ostracods based merely on shell morphology [1,19,20]. The current taxonomic assignment of many fossil ostracods, especially Palaeozoic forms, may be flawed.…”

“…A marked adductorial sulcus and prominent lobation are features typical of Palaeocopida [39], the diverse and abundant Palaeozoic ostracod group that is known from carapaces alone and comprises some 500 genera (D. J. Siveter 2008, unpublished data), although the majority of palaeocopes characteristically have an adventral structure(s), which is lacking in P. avibella. P. avibella and the three other known Palaeozoic myodocope species with soft-parts, Nymphatelina gravida, Nasunaris inflata and Colymbosathon ecplecticos (figure 2a, k-m; [18][19][20]), show a diversity of carapace morphologies even though their soft-parts indicate that all four are myodocopids and all but Nymphatelina are cylindroleberidids (these assignments receive independent support from molecular/morphological analysis of fossil and Recent ostracods [40]). This confirms that carapace morphology alone is an inadequate basis for suprageneric assignment of (Recent) myodocopes [41].…”

“…The soft-parts of ostracods are rarely fossilized [13,14]. From the Palaeozoic a single ostracod-type limb is known from the Late Cambrian [15]; a podocopid specimen with some soft-parts [16] and an undescribed, partially open carapace with poorly preserved limbs [17] from the Devonian; and three myodocope species, each based on an essentially completely preserved specimen, from the Herefordshire (Silurian) Konservat-Lagerstätte, UK [18][19][20]. Here, we describe a new ostracod with soft-parts from the Herefordshire deposit, Pauline avibella gen. et sp.…”

On the genus Thaumatoconcha Kornicker and Sohn (Halocyprida) with description of two new species from Southern Ocean deep sea

“…This is supported mostly by the cladistic analysis of the morphological characters (Baltanás and Danielopol 1995;Danielopol et al 2000) and by the presence of two fossil genera Pokornyopsis Kozur, 1974 andThaumatomma Kornicker andDanielopol, 1976 in waters not deeper than 200 m. The carapace shape of the two fossil taxa is indeed very similar to the present-day Danielopolina species, with some differences in the level of calcification and type of ornamentation (see Danielopol et al 2000), but until now no soft body has been found preserved in the fossil record. Most recently, Siveter et al (2010) described a myodocopid ostracods from Silurian deposits with preserved soft parts, which indicate that this species belongs to the family Cylindroleberididae, but the appearance of the carapace relate it more to the other families, especially Cypridinidae and Sarsiellidae, questioning the utility of the carapace alone in establishing the affinity of fossil ostracods. Only one Danielopolina species, D. carolynae, lives in the deep see.…”

The 2014 recipient of the Brady Medal: Professor David J. Siveter

“…sea spiders, Siveter et al, 2004;barnacles, Briggs et al, 2005), molluscs (Sutton et al, 2001b and polychaetes (Sutton et al, 2001c). The discovery of ostracods with soft-parts has yielded perhaps the most impressive results, certainly with respect to the ethos of this society (Siveter et al, 2003a(Siveter et al, , 2010) -including sexual dimorphism and brood care in the Silurian and then in the Ordovician (Siveter et al, 2014). All of the ostracods found in Herefordshire so far turn out to be members of the living nekto-benthonic myodocope group, some with appendage characteristics remarkably close to the living forms, but with a range of carapace bauplan.…”