An Unusual Echinoderm Assemblage from the Earliest Bajocian of Luxembourg

L.D. Numberger-Thuy & B. Thuy An unusual echinoderm assemblage from the earliest Bajocian of Luxembourg

An unusual echinoderm assemblage from the earliest Bajocian (middle Jurassic) of Luxembourg, with special emphasis on the ophiuroids (Echinodermata: Ophiuroidea)

Lea D. Numberger-Thuy1, 2 & Ben Thuy1 1 Musée national d'histoire naturelle du Luxembourg, section paléontologie, 25, rue Münster, L-2160 Luxembourg 2 [email protected]

Zusammenfassung Die Mehrheit der Stachelhäutervergesellschaftungen Balanocrinus, ein Balanocidaris-artiger Psychocidaride, aus dem Bajocium wurden aus Ablagerungen von und benthopectinide und korethrasteride/pterasteride Karbonatplattformen beschrieben. Im Nordwesten der Seesterne, welche allesamt in Karbonatplattformsedi- Tethys haben diese Ablagerungen aussergewöhnlich menten des nordwestlichen Tethysrandes entweder häufige Funde von artikulierten Resten geliefert, was ganz fehlen oder nur sehr selten vorkommen. Im eine starke Habitat-bezogene Verzerrung des Fossilbe- Gegenzug deuten sie auf einen stärkeren offen-oze- richts der Stachelhäuter im Bajocium bewirkt. Siliziklas- anischen Einfluss hin. Die Schlangensternreste, hier tische Ablagerungen hingegen haben bisher wesentlich ausführlich beschrieben, umfassen fünf Arten, wovon weniger Beachtung bezüglich ihrer möglichen Echino- eine als neu (Lapidaster hellersi sp. nov.) beschrieben wird. dermenfunde erhalten. In der vorliegenden Arbeit wird Letztere gehört zu einer ophiacanthiden Gattung, die im eine Vergesellschaftung von Echinodermen aus einer Bajocium bisher nur aus Tiefwasserablagerungen der dünnen, lateral begrenzten Schicht aus sandigem Ton westlichen Tethys bekannt war und somit die offen-oze- mit Phosphoritknollen beschrieben, die in Rumelange, anischen Affinitäten der restlichen Echinodermen unter- Luxemburg, am nordöstlichen Rand der jungen mauert. Die vorliegende Arbeit bekräftigt das Beachten Burgund Plattform aufgeschlossen sind und auf das von Ablagerungsräumen bei Untersuchungen der früheste Bajocium datiert wird. Die Vergesellschaftung Paläobiodiversität, die ungewöhnlich oder Lagerstätten umfasst den rätselhaften Cyclocrinus, den Isocriniden gegenüber weniger attraktiv erscheinen.

Abstract The vast majority of Bajocian echinoderm assemblages pectinid and korethrasterid/pterasterid asteroids, which have been reported from carbonate platform settings. In lack from or only very rarely occur in Bajocian carbonate the northwestern Tethys, these deposits have produced platform deposits of the northwestern Tethys margin. exceptionally abundant articulated remains, thus intro- Instead, they point to a more open ocean affinity. The ducing a strong palaeo-habitat bias in the Bajocian ophiuroid assemblage, described in detail, includes echinoderm fossil record. Siliciclastic deposits, in five species, one of which is formally described as new contrast, have received surprisingly little attention with (Lapidaster hellersi sp. nov.). The latter belongs to the respect to their potential echinoderm content. Here, ophiacanthid genus Lapidaster which is known only we describe an echinoderm fauna from a thin, laterally discontinuous sandy clay bed rich in phosphorite from deep-water deposits of the western Tethys in the nodules exposed in Rumelange, Luxembourg, on the Bajocian, thus corroborating the open ocean affinities of northeast margin of the incipient Burgundy Platform, the other echinoderms. Our study endorses the inclusion and dated to the earliest Bajocian. The assemblage in palaeo-biodiversity surveys of depositional settings includes the enigmatic Cyclocrinus, the isocrinid Balano- which might seem unusual or less promising than crinus, a Balanocidaris-like psychocidarid, and bentho- Lagerstätten.

Résumé La majorité des collections d'échinodermes du Bajocien ont fourni des fossiles d'échinodermes articulés excep- proviennent de sédiments de plateformes carbonatées. tionnellement abondants, ce qui a créé un fort biais dans Au nord-ouest de la Téthys, les gisements en question le registre fossile bajocien des échinodermes pour les

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types d'habitats correspondants. Les gisements siliciclas- très rarement trouvés dans les gisements bajociens de tiques par contre n'ont reçu que peu d'attention quant au plateforme carbonatée de la bordure nord-ouest de la potentiel de fournir des fossiles d'échinodermes. Dans le Téthys. Les ophiures, décrites en détail, comprennent présent travail, une collection d'échinodermes provenant un total de cinq espèces, dont une nouvelle (Lapidaster d'une couche lenticulaire d'argile sableuse de faible hellersi sp. nov.) appartenent au genre ophiacanthide épaisseur riche en concrétions phosphoritiques, exposée Lapidaster qui n'est connu au Bajocien que de sédiments à Rumelange, Luxembourg, sur la bordure nord-est de la de mer profonde de la Téthys de l'Ouest. Cette obser- plateforme de Bourgogne naissante et datée du Bajocien vation corrobore le charactère plutôt océanique des autres basal. La collection inclut le crinoïde énigmatique Cyclo- groupes d'échinodermes de la collection. Le présent crinus, l'isocrinide Balanocrinus, un psychocidaride proche travail met l'accent sur l'inclusion dans les analyses de de Balanocidaris ainsi que des astérides benthopectinides paléo-biodiversité de gisements qui, à première vue, et korethrasterides/pterasterides, qui ne sont pas ou que semblent moins prometteurs que les Lagerstätten.

Introduction Bajocian (Thuy, this volume), which is well in line with the general trend observed in the survey of Bajocian echinoderms. Dissociated ophiuroid The Bajocian is among the stages that have lateral arm plates, which are known to allow produced outstandingly well known and diverse for much more exhaustive palaeobiodiversity echinoderm remains. Most noteworthy are the assessments than the patchy record of articu- exceptionally preserved and abundant, intact lated skeletons, have only recently come into the layers of echinoderms on the Bahama-type focus of taxonomic surveys (Thuy 2013; Thuy this Burgundy carbonate platform deposits such as volume). the widespread Hauptrogenstein Formation, including remains of all five extant classes (Hess Here, we present a new echinoderm assemblage, 1972; Hess & Holenweg 1985; Hess & Meyer comprising disarticulated remains of crinoids, 2008; Thuy & Meyer 2012). Echinoderms are echinoids, asteroids and ophiuroids, retrieved only preserved intact under certain sedimento- from sieving residues of a sandy clay bed rich in logical and taphonomic conditions (Ausich 2001). phosphorite nodules exposed on the northeast Therefore, although these articulated assemblages margin of the incipient Burgundy Platform. The gained a lot of interest in the past, they represent aim is to contribute to a more complete picture of just a small part of the total echinoderm diversity shallow-water echinoderm biodiversity during during the Bajocian. the Bajocian by focusing on siliciclastic depositional settings which, compared to carbonate The exceptionally preserved echinoderm assem- platform deposits, are strongly undersampled. blages from the Burgundy Platform Lagerstätten The faunal spectrum is highly unusual, comprising originate from a limited number of depositional echinoderm taxa which are only very rarely, settings (Hess & Meyer 2008). In fact, almost all if at all, found in the coeval and later carbonate published records in this respect originate from platform settings. We provide a very brief general oolithic to detrital sand wave obrution deposits overview on the echinoid, crinoid and asteroid (Hess 1972; Hess & Meyer 2008). The abundance taxa with the aim to spark more detailed investi- and exceptional preservation of the echinoderm gations, and provide a detailed assessment of the fossils in question makes them particularly ophiuroid assemblage. attractive for both collectors and researchers, and thus introduces a strong bias in the Bajocian echinoderm fossil record towards shallow-water, high energy carbonate platform assemblages. Geological context Reefal, peri-reefal and, in particular, siliciclastic settings are heavily underrepresented, at least for The here described assemblage was predomi- the non-echinoid echinoderms. nantly retrieved from sieving residues of a 0,10 m In the particular case of the ophiuroids, it is thin, laterally discontinuous bed of grey sandy clay noteworthy that, until recently, only species based with pea- to walnut-sized phosphorite nodules on articulated skeletons were known from the and numerous abraded and encrusted belemnite

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rostra, approximately 1 m above the base of the Material and methods Micaceous Marls. The sand size fraction of the sandy clay predominantly consists of quartz More than 200 echinoderm plates and spines, grains and iron ooids. The bed was dated to the assignable to echinoids, asteroids, crinoids and earliest Bajocian Discites Zone (Walkeri Subzone) ophiuroids, were examined in the present study. based on ammonite evidence (Guérin-Franiatte & Some of the larger remains were picked in the field Weis 2010). It is exposed on the shores of a pond from the weathered surface of the sandy claybed. on an artificial plateau in the former "Hutbierg" The vast majority of the specimens, however, was opencast mine in Rumelange, Luxembourg. retrieved from sieving residues. The coarse (> 5 mm) fraction was screen-washed and picked directly in The nodule bed is highly fossiliferous, in contrast the field, taking advantage of the nearby pond. The to the over- and underlying marls, and yields, apart smaller fraction was screen-washed in a laboratory from the here described echinoderms, abundant sink. No chemical treatment was necessary. cephalopod remains (mainly belemnite rostra, Specimens from the smaller residue fractions were occasional ammonites), bivalves, gastropods, picked under a dissecting microscope. Selected millimeter-sized brachiopods, solitary corals, specimens were cleaned in an ultrasonic bath, then sponges and bryozoans. The micaceous marl either photographed using a VEHO USB camera, succession including, at its base, the sandy clay or mounted on aluminium stubs and gold-coated bed yielding the here-described echinoderms, for scanning electron microscopy (SEM) using a was deposited under falling sea-level conditions JEOL Neoscope JMC-5000. at, or shortly before, the onset of the Burgundy In the particular case of the ophiuroids, identifica- Platform formation (Boulvain et al. 2001; Brigaud tions, if possible to species level, were exclusively et al. 2009, 2013). The general geological context based on the lateral arm plates (abbreviated in the of the area suggests deposition in a shallow to descriptions as LAPs), following the terminology mid-shelf setting, at or slightly below storm wave and recommendations of Thuy and Stöhr (2011). base (Pieńkowski et al. 2008). Higher-level classification follows Smith et al.

Fig. 1: Locality map showing the position of the studied site (marked by a star).

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Fig. 2: Stratigraphic log with the position of the sandy clay bed (marked by a star) that yielded the here described echinoderm assemblage, modified from Weis and Guérin-Franiatte (2010).

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(1995).All type, figured and additional specimens tional find of an articulated arm fragment. Gonias- were deposited in the collection of the Natural terids are commonly found in Middle Jurassic History Museum Luxembourg (MnhnL), under echinoderm assemblages of the peri-Tethys, series number BU. including those from carbonate platform settings (e.g. Hess 1972). The most remarkable asteroid remains, however, are much smaller marginals Results and ambulacrals which are assignable to the Benthopectinidae (Fig. 3 g), as well as adambu- lacrals which show clear korethrasterid-grade pterasterid affinities (Fig. 3 h). The presence of The crinoids these two asteroid groups is noteworthy because their remains have only recently been shown to The echinoderm assemblage studied herein occur in Jurassic sediments on the basis of robust, is markedly dominated by the conspicuous unambiguous morphological evidence based on columnals of Cyclocrinus rugosus (d'Orbigny, 1841) dissociated plates (Gale 2011). The here presented (Fig. 3 a-d). Hess (2008) recently revised the genus benthopectinid and pterasterid records are among Cyclocrinus and summarised its currently known the oldest of the groups and significantly add to occurrences. In spite of more than two decades of their yet very sparse fossil record. research, not a single cup plate has been identified so far, precluding any robust conclusions on the higher taxonomic classification of the genus. The The echinoids here presented specimens fail to add to the debate as they exclusively consist of columnals. The Various test and spine fragments have been material is nevertheless noteworthy as it ranks recorded but one type of primary spines is particu- among the very few Bajocian occurrences of the larly noteworthy (Fig. 3 i-j), first because it is the genus. It might even be the oldest known record most common echinoid remain in the assemblage, of Cyclocrinus. and second because it is not or only rarely found in Almost all other crinoid remains from the here Bajocian carbonate platform deposits. The spines described assemblage are assignable to the in question are small, stout, short, glandiform isocrinid genus Balanocrinus (Fig. 3 e-f). In a recent with a rounded, blunt distal tip and a shaft revision of the taxonomic concept and fossil ornamented with beaded ribs developing into an record of Balanocrinus, Hess (2013) highlighted irregular granulation towards the distal tip of the the abundance of the genus in Lower and Upper spine. The distinctive spine morphology suggests Jurassic mudstones. Middle Jurassic occurrences assignment to the Psychocidaridae. Although of the genus, and even more Bajocian ones, are Caenocidaris is the typical Middle Jurassic repre- less common and predominantly found in areas sentative of the family (e.g. Vadet 1991), similar- of the northwester Tethys margin which are closer ities of the here described material are greater to the open ocean (e.g. Hess & Pugin 1983; Hess with the spines of the late Jurassic Balanocidaris, in 2012). Almost all Middle Jurassic peri-Tethyan particular with respect to the blunt distal tip and assemblages, in particular those of the carbonate the fine ornamentation of the shaft (Smith & Kroh platforms, are dominated by other isocrinids 2010). (Chariocrinus, Hispidocrinus and Pentacrinites) (e.g. Hess 1972; Thuy & Meyer 2012). Typical Caenocidaris commonly occurs in Bajocian carbonate platform settings (e.g. Vadet & Slowik 2001; Thuy 2003). The more Balanocidaris-like The asteroids spine type presented herein, in contrast, has not been reported previously, except for the spine Asteroid fossils are surprisingly abundant in the figured by Thuy (2010) from the earliest Bajocian here presented assemblage. The most conspicuous of Differdange, Luxembourg (Plate 2, fig. h) which remains are large, dissociated goniasterid was found in stratigraphically and sedimentologi- marginals, which are complemented by the excep- cally comparable settings.

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Fig. 3: Echinoderm remains from a sandy clay bed with phosphorite nodules approximately 1 m above the base of the micaceous marls, Discites Zone, Walkeri Subzone, earliest Bajocian, Middle Jurassic, of Rumelange, Lux- embourg. Cyclocrinus rugosus (d'Orbigny, 1841), a-d: HU 306, columnals in facet (a, c) and lateral (b, d) views; Balanocrinus sp., e: HU 322 pluricolumnal in lateral view; f: BU 337, columnal facet; Benthopectinid asteroid, g: BU 338, ambulacral; Korethrasterid/Pterasterid asteroid, h: adambulacral; Psychocidaroid echinoid, i-j: HU 321, primary spines. Scale bars equal 5 mm in a-e and i-j; 500 µm in f, and 250 µm in g-h.

The ophiuroids taxa are among the most abundant (e.g. Thuy & Meyer 2012; Thuy this volume). The ophioder- Our study includes the first exhaustively described matid Ophiotitanos is reported for the first time ophiuroid assemblage from non-carbonate from Bajocian deposits by Thuy (this volume) platform deposits for the Bajocian. Although the and seems to be a rather common component of diversity is low, with only five species identified, coeval carbonate platform deposits, judging from the composition of the ophiuroid assemblage unpublished preliminary survey based on disso- is rather unusual for the Bajocian. It shares the ciated LAPs. The occurrence of the ophiacanthid ophiacanthid Alternacantha and the ophiolepidid Lapidaster, in contrast, is unusual since the genus Enakomusium with coeval ophiuroid assemblages is only known from deep-water sediments of the from carbonate platform settings, where these western Tethys in the Bajocian (Thuy 2013).

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Systematic palaeontology near the row of spine articulations; narrow band of much more finely meshed stereom lining proximal edge of LAP. Three medium-sized, free-standing Class Ophiuroidea Gray, 1840 spine articulations on distal edge of LAP; clear Order Ophiurida Müller & Troschel, 1840 dorsalward increase in size of spine articulations Family Ophiacanthidae Ljungman, 1867 and of gaps separating them; spine articulations ear-shaped, composed of thin dorsal and ventral Genus Lapidaster Thuy, 2013 lobes, proximally separated by a shallow notch and Type species: Lapidaster hystricarboris Thuy, 2013 distally connected by a sigmoidal fold; spine articu- Lapidaster hellersi sp. nov. lations separated from distal edge of LAP by a gap Fig. 4a-f narrower than half a spine articulation. Derivation of name: Species named in honour Inner side of LAP with well defined, thin, arcuate of our step father (in law) Marcel Hellers, for ridge, with oblique, dorso-proximalwards pointing his friendship and his companionship during and dorsalwards tapering dorsal part, and shorter, fieldwork, and in recognition of his contributions wider ventro-proximalwards pointing ventral part to invertebrate zoology. merged with ventral portion of LAP; dorsal and ventral parts of ridge connected by rounded kink. Types: BU 321 (holotype); BU 322, BU 323 Poorly defined, weakly prominent, oblique spur (paratypes) on inner distal edge, composed of more densely Other material: BU 324 (12 dissociated LAPs) meshed stereom. Very large, deeply concave tentacle notch, bordered by thickened ventral Type locality: Pond shore on artificial plateau, edge of the LAP and with horizontally stretched former "Hutbierg" opencast mine in Rumelange, stereom. No perforations discernible. Luxembourg. Paratype supplements and variation: BU 322 is Type horizon: Sandy clay bed with phosphorite a very small proximal to median LAP, almost 1.5 nodules approximately 1 m above the base of the times wider than high; dorsal edge gently convex; micaceous marls, Discites Zone, Walkeri Subzone, ventro-proximalwards pointing ventral portion earliest Bajocian, Middle Jurassic. of LAP smaller than in holotype and with weakly convex ventro-proximal edge; proximal edge Diagnosis: Species of Lapidaster with very small, strongly concave, with kink in ventral half; no horizontally elongate LAPs; outer surface with very spurs on outer proximal edge. Outer surface with coarsely meshed stereom transformed into a weakly very coarsely meshed stereom, with no vertical to moderately well developed, irregular vertical stripes. Three spine articulations as in holotype striation near the spine articulations; very weakly separated from distal edge of LAP by a gap as wide developed, oblique spur on the outer proximal and as half a spine articulation. inner distal edges of the LAP; three spine articulations; inner side of LAPs with narrow, well defined Inner side of LAP as in holotype. ridge with dorsalwards tapering dorsal portion. BU 323 is a very small distal LAP, almost two Description of holotype: BU 321 is a very small times wider than high; dorsal edge straight; ventral proximal LAP; slightly wider than high; dorsal quarter strongly ventro-proximalwards pointing, edge fragmented but originally weakly convex with very weakly concave ventral and ventro- or straight; proximal edge strongly concave, proximal edges. Outer surface as in holotype but with very weakly defined, poorly prominent and with shorter vertical stripes. Three spine articula- non-protruding, oblique spur between ventral and tions as in holotype but separated from distal edge median third of proximal edge; ventral third of by gap as wide as half a spine articulation. LAP strongly ventro-proximalwards protruding, Inner side with moderately well defined, short with concave ventro-proximal edge; ventro-distal ridge, with wide ventral basis and narrow, dorso- tip of LAP weakly protruding ventralwards; very proximalwards pointing, dorsal extension. large, deeply concave tentacle notch. Outer surface with very coarsely meshed stereom, with trabecular Remarks: The genus Lapidaster was introduced intersections merged into irregular, vertical ridges by Thuy (2013) to accommodate dissociated

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ophiuroid LAPs which are essentially similar to protruding ventralwards.. Outer surface with well those of extant Ophiologimus but differ in displaying developed, vertical striation, with stripes largest in spurs on the outer proximal and inner distal edges. dorso-distal part of outer surface, disintegrating into The here described LAPs comply with the diagnosis coarsely meshed stereom towards ventral and distal of Lapidaster in particular with respect to the strongly edges of LAP; narrow band of finely meshed stereom ventro-proximalwards pointing ventral portion of the lining proximal edge. Three large, ear-shaped, nearly LAP, the spur on the outer proximal and inner distal equidistant spine articulations in shallow notches of edges, the large tentacle notches, the ear-shaped distal edge, moderately deeply incising outer surface spine articulations which are neither on an elevated stereom; median spine articulation largest. ridge nor sunken into depressions of the distal edge, Inner side of LAPs with well defined, prominent, and the shape of the ridge on the inner side. simple, arcuate ridge, with very weakly widened, Within this genus, similarities are greatest with the blunt, well defined dorsal and ventral tips. Two to LAPs of Lapidaster fasciatus (Kutscher & Villier, 2003) three well defined, horizontally elongate, prominent from the Toarcian-Aalenian of Germany and France, spurs on inner distal edge. Small but very deep and L. varuna Thuy, 2013 from the Callovian of India. tentacle notch. One to two small, irregular perfora- The here described material differs in the smaller tions dorsally bordering inner side of tentacle notch. size of the LAPs, lower number of spine articulations Remarks: Alternacantha occulta was amply described (three rather than four), the lower height/width ratio, on the basis of articulated skeletons (Thuy & Meyer the weakly developed vertical striation on the outer 2012) and dissociated LAPs (Thuy 2013). The surface, and the dorsalwards tapering dorsal part of examined specimens are all from median to distal the ridge on the inner side of the LAPs. In particular arm positions. A reliable assessment of the full set the latter character is not related to size or- ontoge of diagnostic characters is ideally based on proximal netic stage (Thuy & Stöhr 2011), which prompts us LAPs (Thuy & Stöhr 2011). This is particularly the to consider the here described LAPs as belonging to case in the Alternacantha-Dermocoma group, species a new species. of which commonly have indistinguishable median The new species adds to the sparse middle Jurassic to distal LAPs (Thuy 2013). Therefore, in spite of the fossil record of the genus, closing a gap in the strong similarities with the median LAPs of Alterna- shallow-water record between the earliest Aalenian cantha occulta figured by Thuy and Meyer (2012) and Lapidaster fasciatus and the Callovian L. varuna (Thuy Thuy (2012), we consider the species-level assignment 2013). The only other middle Jurassic species of the as tentative. genus is Lapidaster wolfii Thuy, 2013 from Bajocian- Bathonian bathyal sediments of France. Family Ophiodermatidae Ljungman, 1867 Genus Ophiotitanos Spencer, 1907 Genus Alternacantha Thuy & Meyer, 2012 Type species: Ophiotitanos tenuis Spencer, 1907, by Type species: Alternacantha occulta Thuy & Meyer, original designation. 2012, by original designation. Ophiotitanos sp. Alternacantha cf. occulta Thuy & Meyer, 2012 Fig. 4g Fig. 4h-i Material examined: BU 335, and BU 336 (2 disso- Material examined: BU 325, and BU 326 (4 dissociated LAPs). ciated LAPs in total). Description: Median to distal LAPs, as high as wide to Description: Large dissociated median to distal almost 1.5 times wider than high; with ventro-proxi- LAPs, as high as wide or slightly wider; with malwards protruding ventral fifth in median LAPs to strongly concave dorsal edge as a result of a strong rounded rectangular in outline in distal ones;ventral constriction; proximal edge weakly concave, with up and distal edges weakly convex; dorsal edge gently to four poorly to moderately well defined, slightly convex in median LAPs, straight in distal ones; prominent and protruding spurs; ventral third proximal edge irregularly concave, tapered, with very large and strongly protruding ventro-proxi- two large, poorly developed and weakly prominent malwards; ventro-distal tip of LAP tongue-shaped, spurs on the ventro-distal and dorso-distal tips; outer

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Fig. 4: Dissociated ophiuroid lateral arm plates (LAPs) from a sandy clay bed with phosphorite nodules approximately 1 m above the base of the micaceous marls, Discites Zone, Walkeri Subzone, earliest Bajocian, Middle Jurassic, of Rumelange, Luxembourg. Lapidaster hellersi sp. nov., a-b: BU 321 (holotype), proximal LAP in external (a) and internal (b) views; c-d: BU 322 (paratype), median LAP in external (c) and internal (d) views; e-f: BU 323 (paratype), distal LAP in external (e) and internal (f) views; Ophiotitanos sp., g: BU 335, median to distal LAP in external view and with detail of spine articulation (l). Alternacantha cf. occulta Thuy & Meyer, 2012, h-i: BU 325, distal LAP in external (h) and internal (i) views. Eozonella sp. nov., j-k: BU 327, proximal LAP in external (j) and internal (k) views; l-m: BU 328, median LAP in external (l) and internal (m) views; n-o: BU 329, distal LAP in external (n) and internal (o) views. Scale bars equal 250 µm.

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surface with finely meshed stereom, with trabecular Material examined: BU 327, BU 328, BU 329; and intersections transformed into small, inconspicuous BU 330 (20 dissociated LAPs) tubercles. Four to five nearly equal-sized spine Description: Very small, fragile dissociated LAPs, articulations sunken in shallow notches of the distal elongate, 1.5 (proximal LAPs) to 2.5 (distal LAPs) LAP edge, with weak dorsalward increase in size of wider than high, rounded outline, with convex gaps separating the spine articulartions; notches of dorsal, distal and ventral edges; ventral quarter the spine articulations tightly encompassed by outer of proximal and median LAPs protruding ventro- surface stereom and separated by distalward projec- proximalwards; proximal edge concave, with two tions of the latter; spine articulations composed of poorly defined, slightly prominent and protruding a large, crescent-shaped dorsal lobe and a smaller spurs composed of slightly more densely meshed ventral lobe; lobes proximally merged by a thin ridge. stereom, one in the middle of the proximal edge, Inner side of median LAPs unknown due to poor the second in the middle of the ventral half of preservation; distal LAPs with large, conspicuous the proximal edge. Outer surface of LAPs with contact surfaces with opposite LAP; small, incon- moderately coarsely meshed stereom devoid of spicuous, well defined ridge with proximalwards any conspicuous ornamentation; narrow band bent, pointed dorsal tip; two moderately large, poorly of slightly more finely meshed stereom lining defined and hardly prominent spurs composed of proximal edge of LAPs. Three (proximal and slightly more densely meshed stereom on inner distal median LAPs) to two (distal ones) small, equal- edge. Large, round tentacle perforation between the sized and equidistant spine articulations sunken distal and middle third of the inner side, proximally into and tightly surrounded by outer surface bordering the ventral spur. No other perforation or stereom at distal edge of LAPs; spine articulations furrow discernible. composed of horizontal, nearly parallel dorsal and ventral lobes composed densely meshed stereom, Remarks: The available material is very limited proximally separated by two to three very small, both in terms of abundance and preservation. To irregular knobs. make matters worse, only median to distal LAPs are available. This is unfortunate considering that the Inner side of LAPs with sharply defined, analysis of Thuy and Stöhr (2011) clearly showed that prominent ridge composed of more finely meshed identifications of dissociated LAPs should be based stereom, with round, ventralwards pointing on adult, proximal plates. The here proposed identifi- ventral portion not merged with ventral part of cation is thus to be considered as preliminary. LAP, and slightly tapering dorso-proximalwards pointing dorsal portion. Well defined, elongate, The above described LAPs share striking similar- strongly oblique, prominent spur on the ventro- ities with the median and distal LAPs described by distal tip of the inner side of the LAP. Large, deep Thuy (this volume) as the new species Ophiotitanos tentacle notch on all LAPs, bordered by slightly aschmannicor. The spine articulation morphology of thickened edges of ventral portion of LAP. No the LAPs at hand, however poorly preserved, corrob- perforations or furrow discernible. orates assignment to the Ophiodermatidae. Awaiting the discovery of more complete material, and in Remarks: The LAPs described above are unambig- particular of well preserved proximal LAPs, and in uously assignable to the group of ophiolepidids the light of the similarities with the LAPs of near- comprising extant Ophiozonella Matsumoto, 1915 coeval Ophiotitanos aschmannicor, we thus consider and its morphologically very similar extinct the above described material as undetermined record relative Eozonella Thuy, Marty & Comment, 2013, of Ophiotitanos. on account of the outline of the LAPs, the ventro- proximalwards protruding ventral portion, the spurs on the outer proximal and inner distal edges, Family Ophiolepididae Ljungman, 1867 the shape of the ridge on the inner side, and the Genus Eozonella Thuy, Marty & Comment, 2013 shape and position of the spine articulations. When Type species: Eozonella bergeri Thuy, Marty & introducing the new genus Eozonella to accom- Comment, 2013, by original designation modate extinct Ophionella-like ophiuroids, Thuy et al. (2013) worked out clear-cut differences between Eozonella sp. nov. the two in terms of general skeletal morphology. Figs. 4j-p They stressed, however, that both share very

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similar LAP morphologies. A LAP-based diagnosis (median to distal LAPs) spurs composed of of Eozonella is yet to be put forward. The shape slightly more densely meshed stereom; proximal and position of the spurs on the outer proximal edge paralleled by a deep, conspicuous furrow. and inner distal edges as well as the absence of a Outer surface with coarsely meshed stereom, fine horizontal striation lining the outer proximal with irregularly angular, pointed trabecular edge of the LAPs suggest assignment of the here intersections; outer surface stereom mesh size described specimens to Eozonella rather than strongly decreasing towards furrow paral- Ophiozonella, at least when referring to the type leling proximal edge. Four (proximal LAPs) to species Ophiozonella longispina (Clark, 1908). two (distal LAPs) small, prominent but poorly discernible spine articulations integrated into Three species have been assigned to Eozonella so far, and tightly surrounded by outer surface stereom; namely the type species E. bergeri, the Oxfordian spine articulations separated from distal edge by E. oertlii (Hess, 1965) and the Bajocian/Bathonian a gap as wide as the spine articulations or slightly E. bathonica (Hess, 1964). All three display much narrower; dorsalward increase in size of spine larger and stouter LAPs with a higher number articulations and of gaps separating them; large of spine articulations than the here described specimens. We nevertheless refrain from formally gap between dorsalmost spine articulation and introducing a new species as there are some more dorsal edge in proximal LAP; spine articulations named records of Middle Jurassic Ophiozonella-like composed of a small muscle opening ventro- ophiuroids based on articulated skeletons, which proximally tightly encompassed by a coarsely are at present insufficiently know, especially with rugose semi-circular ridge, and distally separated respect to their LAP morphology, and which thus from a slightly smaller nerve opening by a short, cannot be satisfyingly compared with the material vertical, rugose ridge; distal LAPs with conspic- at hand. The records in question are Ophiura tinur- uously enlarged, lip-shaped ridge separating tiensis Valette, 1929 from the Aalenian of France, muscle and nerve openings. Ophiopeza ferrugineum (Boehm, 1889) from the Inner side of LAP with large contact surfaces with Bajocian/Bathonian of Germany and France, and opposite LAP; small, sharply defined, prominent Ophiopeza portei Guillaume, 1926 from the Bathonian ridge with tongue shaped, proximalwards bent of France, which Hess and Meyer (2008) assigned and tapering dorsal tip in proximal LAPs, and to the ophioleucin genus Sinosura on the basis of small, poorly defined triangular ridge in median very limited morphological evidence. Pending a to distal ones. Deep, narrow but sharply defined, detailed re-assessment of the type specimens of ventralwards pointing tentacle notch in proximal these species, we treat the material at hand as an to median and sometimes even distal LAPs; large, unknown, most probably new species of Eozonella. round tentacle perforations in median to distal LAPs. Two poorly defined, non-prominent spurs on inner distal edge, composed of more densely Family unnamed (see O'Hara et al. 2014) meshed stereom. No perforation discernible. Genus Enakomusium Thuy, this volume Remarks: The above described LAPs display the Type species: Ophioderma weymouthiense Damon, combination of characters typically found in the 1880, by original designation. genus Enakomusium, introduced by Thuy (this Enakomusium cf. ferrugineum (Boehm, 1889) volume) to accommodate ophiuroids which are Fig. 5 superficially similar to extant Ophiomusium but which differ in a higher number of between-plate Material examined: BU 331, BU 332, BU 333; and tentacle openings (in contrast to within-plate BU 334 (42 dissociated LAPs) tentacle perforations) per arm, a generally rounder Description: Medium-sized dissociated LAPs, outline of the LAPs, and a deep furrow paralleling proximal ones nearly as high as wide, distal ones the proximal LAP edge. The LAPs at hand share 1.5 wider than high, all of rounded rectangular striking similarities with those assigned by Thuy outline, with convex dorsal, distal and ventral (this volume) to Enakomusium ferrugineum from edges; proximal edge weakly concave, with two to the early Bajocian of nearby Longwy, France. three, weakly prominent and protruding, poorly Minor differences pertain to a smaller size, a defined (proximal LAPs) to almost indiscernible lower height/width ratio, a coarser outer surface

Ferrantia • 71 / 2015 49 L.D. Numberger-Thuy & B. Thuy An unusual echinoderm assemblage from the earliest Bajocian of Luxembourg

Fig. 5: Dissociated lateral arm plates (LAPs) of Enakomusium ferrugineum (Boehm) from a sandy clay bed with phosphorite nodules approximately 1 m above the base of the micaceous marls, Discites Zone, Walkeri Subzone, earliest Bajocian, Middle Jurassic, of Rumelange, Luxembourg. a-b: BU 331, proximal to median LAP in external (a) and internal (b) views; c-d: BU 332, median LAP in external (c) and internal (d) views; e-f: BU 333, distal LAP in external (e) and internal (f) views. Scale bars equal 250 µm.

stereom and a higher number of arm segments coeval echinoderm assemblages from carbonate with between-plate perforations. platform deposits is the composition of the crinoid Chances thus are that the here described LAPs fauna. The enigmatic Cyclocrinus is reasonably belong to a new species. It must be reminded, common in siliciclastic settings of Bathonian however, that the assignment of the material to Oxfordian age but Bajocian occurrences are described by Thuy (this volume) to E. ferrugineum exceedingly rare (Hess 2008). The second common is based on comparison with non-type articulated crinoid of the here described assemblage is a skeletons. Considering that currently known species of Balanocrinus, an isocrinid which, in species of Enakomusium show highly similar LAP contrast to its relatives such as Chariocrinus, Hispi- morphologies, and pending a detailed re-exami- docrinus and Pentacrinites, generally lacks from nation of the holotype of E. ferrugineum, in the north-western Tethyan carbonate platform particular with respect to its LAP morphology, we settings and instead more commonly occurs in refrain from introducing a new species here. siliciclastic deposits, especially those closer to the open ocean of the Tethys (Hess & Pugin 1983; Hess 2012). The asteroids and ophiuroids of the Discussion assemblage at hand corroborate a more open ocean or more Tethyan affinity of the assemblage, The echinoderm assemblage described herein is as they include extant deep-water taxa (Bentho- among the first from the Bajocian of the north- pectinidae and Korethrasteridae/Pterasteridae) western Tethys to be recovered from purely silici- and the extinct Lapidaster which have not yet been clastic sediments. The most striking difference to reported from coeval carbonate platform settings.

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Altogether, the echinoderm fauna described in Brigaud, B., Vincent, B., Carpentier, C., Robin, C., this study seems to document a stronger Tethyan Guillocheau, F., Yven, B. & Huret, E. 2013. - Growth affinity than coeval and slightly younger carbonate and demise of the Jurassic carbonate platform in platform equivalents. Our study endorses the the intracratonic Paris Basin (France): Interplay of inclusion in palaeo-biodiversity surveys of deposi- climate change, eustasy and tectonics. Marine and tional settings which might seem unusual or less Petroleum Geology, doi: http://dx.doi.org/10.1016/j. attractive than those producing more abundant marpetgeo.2013.09.008. and/or articulated remains. As shown here, such Clark, H.L. 1908. - Some Japanese and East Indian settings are likely to yield taxa which would Echinoderms. Bulletin of the Museum of Compar- otherwise pass unnoticed. ative Zoology 51(11): 279-311. Damon, R. 1880. - Supplement to the Geology of Weymouth and the Isle of Portland. 2nd edition. Acknowledgments London. Gale, A. S. 2010. - The phylogeny of post-Palaeozoic We are grateful to Jean-Michel Guinet (Luxem- Asteroidea (Neoasteroidea, Echinodermata). bourg, L) for granting access to the Scanning Special Papers in Palaeontology 85: 1–112. Electron Microscope facilities of the Natural History Museum in Luxembourg, to Roby Weis Guérin-Franiatte, S. & Weis, R. 2010. - Le passage (Luxembourg, L) for inciting submission of the Aalénien-Bajocien près de Rumelange: la série present contribution to Ferrantia, to Marcelline biostratigraphique dans le Bassin d'Esch-sur- Haas (Steinsel, L) who collected some of the Alzette (Grand-Duché de Luxembourg). Ferrantia specimens and donated them to the Natural 62 : 73-96. History Museum Luxembourg, and an anonymous Guillaume, L. 1926. - Ophiopeza portei, Ophiure nouvelle reviewer whose comments greatly improved an du Bathonien supérieur de Ranville (Calvados). earlier version of the manuscript. Compte Rendu Sommaire et Bulletin de la Société Géologique de France 4(26): 117-127. Hess H. 1964. - Die Ophiuren des englischen Jura. References Eclogae geologicae Helvetiae 57: 756-801.

Ausich, W.I., 2001. - Echinoderm taphonomy, in: Hess H. 1965. - Mikropaläontologische Untersu- Jangoux, M., Lawrence, J.M. (Eds.), Echinoderm chungen an Ophiuren IV: Die Ophiuren aus studies 6. Balkema, Rotterdam: 171-227. dem Renggeri-Ton (Unter-Oxford) von Chapois (Jura) und Longecombe (Ain). Eclogae geologicae Boehm, G. 1889. - Ein Beitrag zur Kenntnis fossiler Helvetiae 58: 1059-1082. Ophiuren. Bericht der naturforschenden Gesell- schaft Freiburg. Breslau 4: 232-287. Hess, H. 1972. - Eine Echinodermenfauna aus dem mittleren Dogger des Aargauer Juras. Schweize- Boulvain, F., Belanger, I., Delsate, D., Ghysel, P., rische Paläontologische Abhandlungen 92: 1-87. Godefroit, P., Laloux, M., Monteyne, R., Roche, Hess, H. 2008. - Cyclocrinus, an enigmatic Jurassic-Cre- M. 2001. - Triassic and jurassic lithostratigraphic taceous crinoid. Swiss Journal of Geosciences 101: unites (Belgian Lorraine). Geologica Belgica 4(1-2): 465-481. 113-119. Hess, H. 2012. - Crinoids from the Middle Jurassic Brigaud, B., Durlet, C., Deconinck, J.-F., Vincent, B., (Bajocian-Lower Callovian) of Ardèche, France. Pucéat, E., Thierry, J. & Trouiller, A. 2009. - Facies Swiss Journal of Palaeontology 131: 211 - 253. and climate/environmental changes recorded on a carbonate ramp: A sedimentological and Hess, H. 2013. - Balanocrinus (Crinoidea) from the geochemical approach on Middle Jurassic Jurassic: species concept, reconstruction, ontogeny, carbonates (Paris Basin, France). Sedimentary taphonomy and ecology. Swiss Journal of Palaeon- Geology 222: 181-206. tology. http://dx.doi.org/10.1007/s13358-013-0062-2.

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Hess, H. & Holenweg, H. 1985. - Die Begleitfauna perspectives. Zoological Journal of the Linnean auf den Seelilienbänken im mittleren Dogger des Society 114: 213-243. Schweizer Juras. Tätigkeitsberichte der Naturfor- Spencer, W.K. 1907: A Monograph of the British Fossil schenden Gesellschaft Baselland 33: 141–177. Echinodermata from the Cretaceous formations. Hess, H. & Meyer, C.A. 2008. - A new ophiuroid Volume second: The Asteroidea and Ophiuroidea. (Geocoma schoentalensis sp. nov.) from the Middle Paleontographical Society Monographs 2(4): 91-132. Jurassic of north-western Switzerland and remarks Thuy, B. 2003. – Les échinides du Bajocien de on the family Aplocomidae Hess, 1965. Swiss Rumelange (Grand-Duché de Luxembourg). Journal of Geosciences 101: 29-40. Ferrantia 36: 79-123. Hess, H. & Pugin, L. 1983. - Balanocrinus berchteni Thuy, B. 2010. - An early Bajocian echinoid fauna from n.sp., un nouveau crinoïde bajocien des Préalpes Differdange and Pétange (Luxembourg), including médianes fribourgeoises. Eclogae geologicae a new Rhabdocidaroid species. Ferrantia 62: 97-114. Helvetiae 76: 691-700. Thuy, B. 2013. - Temporary expansion to shelf depths Kutscher, M. & Villier, L. 2003. - Ophiuroid remains rather than an onshore-offshore trend: the shallow- from the Toarcian of Sainte-Verge (Deux-Sèvres, water rise and demise of the modern deep-sea France): paleobiological perspectives. Geobios 36: brittle star family Ophiacanthidae (Echinodermata: 179-194. Ophiuroidea). European Journal of Taxonomy 48: Matsumoto, H. 1915. - A new classificatioon of the 1-242. Ophiuroidea: with description of new genera and Thuy, B. this volume. - A peri-reefal brittle-star species. Proceedings of the Academy of Natural (Echinodermata : Ophiuroidea) assemblage from Sciences of Philadelphia 68: 43-92. the Middle Jurassic of the northeast Paris Basin. O'Hara, T.D., Hugall, A.F., Thuy, B. & Moussalli, Ferrantia. A. 2014. – Phylogenomic Resolution of the Class Thuy, B., Marty, D. & Comment, G. 2013. - A remarkable Ophiuroidea Unlocks a Global Microfossil Record. example of a Late Jurassic shallow-water ophiuroid Current Biology 24: 1-6. assemblage from the Swiss Jura Mountains. Swiss Orbigny, A. d' (1840–41). - Histoire naturelle, générale Journal of Geosciences 106: 409-426. et particulière, des Crinoïdes, vivants et fossiles, Thuy, B. & Meyer, C.A. 2012. - The pitfalls of extrapo- comprenant la description géologique et zoologique lating present-day depth ranges to fossil commu- de ces animaux. Livr. 1, 1–32 (1840); livres 2–3, nities: new insights from brittle stars (Echino- 33–98 (1841) (republished 1858), published by the dermata: Ophiuroidea) from the Middle Jurassic author. Paris. of Switzerland. Swiss Journal of Palaeontology 132: Pieńkowski G., Schudack M.E., Bosák P., Enay R., 5-21. Feldman-Olszewska A., Golonka J., Gutowski J., Thuy, B., Stöhr, S. 2011. - Lateral arm plate morphology Herngreen G.F.W., Jordan P., Krobicki M., Lathu- in brittle stars (Echinodermata: Ophiuroidea): new ilière B., Leinfelder R.R., Michalik J., Mönnig E., perspectives for ophiuroid micropalaeontology and Noe-Nygaard N., Pálfy J., Pint A., Rasser M.W., classification. Zootaxa 3013: 1-47. Reisdorf A.G., Schmid D.U., Schweigert G., Surlyk F., Wetzel A. & Wong T.E. 2008. Jurassic. In: McCann Vadet, A. 1991. - Revision des "Cidaris" du Lias et du T. (ed.) The geology of central Europe 2: Mesozoic Dogger Europeens. Memoires de la Societe du and Cenozoic: 823-922. The Geological Society, Bolognnais 10 : 1-167, pls 1-9. London. Vadet, A. & Slowik, D. 2001. - Les oursins du Bajocien Smith, A. B. & Kroh, A. 2011. - The Echinoid Directory. de Liocourt. Memoires de la Societe Academique du World Wide Web electronic publication. http:// Boulonnais. Serie Histoire Naturelle 22 : 1-48. www.nhm.ac.uk/research-curation/projects/ Valette, A. 1929. - Note sur quelques stellerides juras- echinoid-directory [accessed 23.01.2014]. siques du Laboratoire de Géologie de la Faculté Smith, A. B., Paterson, G. L. J. & Lafay, B. 1995. - des Sciences de Lyon. Travaux du Laboratoire de Ophiuroid phylogeny and higher taxonomy: Géologie de la Faculté des Sciences de Lyon, 16, morphological, molecular and palaeontological 1-62.

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