782


Journal of Paleontology 91(4):781–798 Almost all material consists of articulated skeletons or parts


of skeletons collected as macrofossils. The series of specimens described by Ewin and Thuy (2015) furthermore includes numerous articulated parts of disks and arms aswell as dissociated skeletal plates collected by bulk sieving in water using a 150 µm mesh. Thanks to the mostly clayey matrix, most studied speci- mens are exquisitely preserved showing original stereom structures. The material was examined using scanning electron


microscopy (SEM), in case of the larger specimens using a Leo LV1455VP low-pressure environmental SEM without coating, and in case of the smaller ones using a JEOL Neoscope JMC-5000 with gold coating. Terminology followed Stöhr et al. (2012) and Thuy and Stöhr (2011). Lateral arm plates are abbreviated as LAPs in the following sections of the manuscript.


Repositories and institutional abbreviations.—All material is housed in the Natural History MuseumLondon (NHMUK) with the exception of the holotype of A. pratti, which is housed at the Geological Survey Museum (BGS), and the specimen figured by Martill and Hudson (1991), which is housed in Leicester University Geology Collections (LEIUG).


Oxford Clay ophiuroid localities, stratigraphy, geology, and taphonomy


In England, the Oxford Clay Formation, middle Callovian– lower Oxfordian, crops out along a southwest/northeast trending band (Fig. 1) from the south coast of Dorset near Weymouth, through Wiltshire, Gloucestershire, and central England and


into Lincolnshire and Yorkshire, where it again meets the coast at Scarborough (Cox and Sumbler, 2002). Owing to the rela- tively unconsolidated nature of the formation, natural outcrops are only seen in areas of constant erosion, essentially coastal areas (Weymouth). However, the Oxford Clay Formation has been exposed in numerous inland areas at different times owing to various excavation activities. Several of these activities have produced the ophiuroid specimens that form the basis of this study (Fig. 1) and include railway line construction (Cheltenham and Christian Malford, Wiltshire in the 1840s; Wilby et al., 2008), quarrying of overlying Pleistocene gravels (Coln Quarry, Gloucestershire; Dr. N. Hollingworth, personal communication, 2015), and clay extraction for brick manu- facture (Westaway et al., 2015). The Callovian of southern and central England represents a


time of steady sea level rise into the Oxfordian (Wright and Cox, 2001). This is reflected in the widespread and laterally con- sistent deposition of the Oxford Clay, which has a silty/sandy base grading into fine and fissile clays and shales with a high organic content. The seas around Britain during the Callovian– Oxfordian were generally warm and clear. Land was located approximately 50–100 km away from any of the studied local- ities and lay mostly to the north, west, and east (Cox and Sumbler, 2002). These lands were presumably the source of intermittent pulses of sediment that buried the ophiuroids. The Oxford Clay Formation is subdivided into Taxon-range


biozones and subzones using ammonites (Cox and Sumbler, 2002) and comprises three members, the lowest Peterborough Member, the middle Stewartby Member (both Callovian), and the upper Weymouth Member (Oxfordian). The Oxford Clay has been the subject of many detailed studies owing to its economic importance as a source of self-firing brick clay and its abundant and exquisitely preserved fossils (Westaway et al., 2015; Martill and Hudson, 1991). The three members of the Oxford Clay Formation are remarkably consistent across their outcrop of over 200km,which is indicative of its deposition during a wide transgression (Cox and Sumbler, 2002). Figure 2 shows the stratigraphy of theOxford Clay in central and southern England and the position of the ophiuroids studied herein. Ophiuroids are known from the Peterborough Member and


Figure 1. Map showing the outcrop surface of the Oxford Clay Formation in Great Britain and the positions of the ophiuroid localities (A: Ophiotitanos smithi, Ophioplax pratti;B: Enakomusium indet. C: Enakomusium whymanae, Aspidophiura seren;D: Enakomusium weymouthiense;E: Dermocoma sp.).


probably (see the following) the Weymouth Member of the Oxford Clay Formation. None have conclusively been found in the Stewartby Member, which is regarded as generally poor in shelly fossils (Cox and Sumbler, 2002). The Kosmoceras jason Taxon-range Biozone of the Peterborough Member has long been known as a source of numerous, exquisitely preserved fossils, particularly from sites near Christian Malford (mainly cephalopods and fish; Wilby et al., 2008) and around the Peterborough brick pits where numerous marine reptiles were collected by the Leeds brothers but which is also known for its abundant invertebrate fauna (Martill and Hudson, 1991). The high diversity and organic content of the sedimentary rock of this member are attributed to high productivity (MacQuaker, 1994; Hudson et al., 1994; Martill et al., 1994). It is the Peter- borough Member that four of the species (from three different localities) described herein come from. The other two species probably come from the Weymouth Member (“upper Oxford Clay”–lower Oxfordian) around the town of Weymouth, which is also well known for its fossil mollusk fauna (Cox and


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