Echinoid Assemblages Research Articles

Taxonomy and significance of Cenomanian echinoids distribution in the Batna Mounts (NE, Algeria)

From 700 echinoids specimens collected from the Cenomanian sediments of Batna Mounts, 16 species (9 regular and 7 irregular) belonging to 11 genera, 10 families and 7 orders, have been identified. One species is reported for the first time from Algeria Pygaulus subaequalis. The irregular echinoids, including the Hemiasteridae remain the most abundant. The abundance, biodiversity and distribution of the echinoids in the Cenomanian deposits leads to recognize echinoid assemblages or echinoid biozones closely related to sea level variation. The identified echinoid biozones are as the following (1) a lower Cenomanian association representing the Hemiaster gabrielis Total Range Zone (Association A) characterizing a relatively deep environment, located distally in the platform; (2) a middle Cenomanian association which comprises the Mecaster aumalensis - M. pseudofourneli Assemblage Zone (Association B) representing a shallower marine environment; (3) two associations in the upper Cenomanian Mecaster batnensis Acme Zone (Association C1) and the first occurrence of the holectypoids (Association C2) which indicates slight bathymetric fluctuation between the lower and upper infralittoral zones; (4) towards the terminalCenomanian, the Mecaster cf. heberti Total Range Zone (Association D), corresponds to a shallow subreefal environment.

Distribution and Diversity of Sediment-Dwelling Echinoids of the Central Florida Keys

Sediment-dwelling echinoids, such as clypeasteroids (sand dollars and sea biscuits) and spatangoids (heart urchins), are important ecosystem engineers found in many soft-bottom habitats around the Florida Keys. Several studies, conducted over the last five decades, have documented their spatial distribution and diversity in various areas of the Florida Keys. This study focuses on the central part of the Florida Keys, an area that has been subject to diverse human impacts including tourism, fishing, boating, and diving leading to pollution, eutrophication, and intrusion of non-native species. All these stressors can potentially undermine the ecosystem’s composition and health, including sediment-dwelling echinoids. To assess the current state of echinoid populations, 27 sites located along the central part of the Florida Keys have been surveyed by SCUBA (2020-2021) for presence of live specimens and dead skeletal remains of clypeasteroid and spatangoid echinoids. A total of 17 out of 27 sites were inhabited by sediment-dwelling echinoids of the species Clypeaster rosaceus, Clypeaster subdepressus, Encope michelini, Leodia sexiesperforata, Meoma ventricosa, and Plagiobrissus grandis. Up to five species co-occurred at single sites, although most sites harbored only one or two species, and at all sites a single species was dominant in terms of relative abundance. The most widespread and abundant species in the surveyed area were Clypeaster rosaceus, Leodia sexiesperforata, and Meoma ventricosa. A comparison of live specimens with skeletal echinoid remains indicates that dead tests are typically much rarer than live specimens. However, the spatial distribution and abundance of dead remains tracks live occurrences: when dead remains are found, live specimens are always observed. The comparison of the new survey reported here with past studies and database records suggests that the faunal composition of sediment-dwelling echinoid assemblages has not changed notably over the past 50 years.

Santonian (Late Cretaceous) echinoids from the Santander area (northern Cantabria, Spain)

Eight echinoid species are described from Upper Cretaceous marl-limestone alternations from a temporary outcrop in the neighbourhood of the village of Mompia (northern Cantabria, Spain): Temnocidaris (Stereocidaris) mengaudi, Pseudoholaster pachecoi, Roweaster cantaber, Micraster turonensis, Micraster mengaudi, Bolbaster micranthus and two newly described species: the phymosomatoid Cosmocyphus cantaber sp. nov. and the micrasterid Micraster quebrada sp. nov. The three Micraster species reveal an astonishing and extreme degree of intraspecific variation, in particular the degree of inflation of the test. This has not yet been detected in any other spatangoid species before. The majority of reported echinoids are restricted to the working area, and hence are likely endemic to this area. An integrated stratigraphic approach using ammonites, inoceramid bivalves, calcareous nannofossils and stable carbon isotopes localises the echinoid assemblage in the upper middle and lower upper Santonian.

Spatial distribution, diversity, and taphonomy of clypeasteroid and spatangoid echinoids of the central Florida Keys.

Irregular echinoids are ecosystem engineers with diverse functional services. Documenting present-day distribution of those widespread organisms is important for understanding their ecological significance and enhancing our ability to interpret their rich fossil record. This study summarizes SCUBA surveys of clypeasteroid and spatangoid echinoids conducted in 2020 and 2021 along the central part of the Florida Keys. The survey included observations on both live and dead specimens, their distribution, habitat preferences, abundance, and live-dead comparison. Echinoids were found at 17 out of 27 examined sites (63%) and occurred across a wide range of habitats including coastal seagrass meadows, subtidal sand and seagrass settings of the Hawk Channel, backreef sands, and fine muddy sands of deeper forereef habitats. The encountered species, both dead and alive, included Clypeaster rosaceus (four sites), Clypeaster subdepressus (five sites), Encope michelini (three sites), Leodia sexiesperforata (eight sites), Meoma ventricosa (nine sites), and Plagiobrissus grandis (four sites). All sites were dominated by one species, but some sites included up to five echinoid species. Live-dead fidelity was high, including a good agreement in species composition of living and dead assemblages, congruence in species rank abundance, and overlapping spatial distribution patterns. This high fidelity may either reflect long-term persistence of local echinoid populations or fragility of echinoid tests that could prevent post-mortem transport and the formation of time-averaged death assemblages. Regardless of causative factors, the live-dead comparisons suggest that irregular echinoid assemblages, from settings that are comparable to the study area, may provide a fossil record with a high spatial and compositional fidelity. The survey of live fauna is consistent with past regional surveys in terms of identity of observed species, their rank abundance, and their spatial distribution patterns. The results suggest that despite increasingly frequent hurricanes, active seasonal fisheries, massive tourism, and urban development, irregular echinoids continue to thrive across a wide range of habitats where they provide diverse ecosystem services by oxygenating sediments, recycling organic matter, supporting commensal organisms, and providing food to predators. Results reported here document the present-day status of local echinoid populations and should serve as a useful reference point for assessing future regional changes in echinoid distribution and abundance.

Aptian–Cenomanian echinoids from northern Sinai, Egypt

Aptian–lower Cenomanian sedimentary rocks, assigned to the Risan Aneiza and Halal formations and exposed in northern Sinai yield rich, well-preserved echinoid assemblages. Thirty-two species (16 regular and 16 irregular), in 27 genera, have been identified and are here systematically described from the Gebel El Tourkumanyia and Wadi El Karm sections (El Maghara area). A new genus, Sinaiosalenia, and two new species, Sinaiosalenia rhombohedralis (lower Cenomanian) and Globator aegyptiaca (middle Albian), both from Gebel El Tourkumanyia, are erected. Additionally, two species are recorded from Egypt for the first time: Emiratia raskhaimahensis Ali, 1990 and Pseudananchys ludovici (Fourtau, 1912).

Els macroforaminífers i la fauna associada del Maastrichtià del sector Prebètic valencià sud (Est de la Península Ibèrica)

Larger foraminifera and associated fauna from the Maastrichtian of the southern valencian Prebaetic sector (E Iberian Peninsula) The benthic foraminiferal assemblage and the associated fauna found in the Upper Cretaceous deposits of the Serra de la Solana, Valencia (Spain) have been revised. The study has allowed us to confirm the presence of the foraminiferal species Hellenocyclina beotica Reichel, Siderolites aff. calcitrapoides Lamarck, Orbitoides apiculata Schlumberger, Orbitoides gensacicus (Leymerie) and Omphalocyclus macroporus (Lamarck), as stated by previous authors. In addition, the revision has permitted to identify some other species, never cited before in Serra de la Solana and neighbour regions in Iberian Peninsula, such as Fissoelphidium operculiferum Smout and Selimina cf. spinalis Inan and two different morphotypes of rotaliids that we have left in open nomenclature, namely, Rotaliidae indet. sp. 1 and Rotaliidae indet. sp. 2. The rudists and echinoid found associated to these benthic foraminifera have been also revised. The rudist species found are Hippurites radiosus Des Moulins, Hippurites cornucopiae Defrance, Hippurites cf. lamarcki Douvillé, and Apricardia sp., the two latter cited in Serra de la Solana for the first time. The echinoid assemblage is composed of the species Pygopyrina darderi (Lambert), Linthia payeni (Coquand) and Hemipneustes striatoradiatus (Leske). The whole assemblage, typical of shallow-water platform environments, is Upper Maastrichtian in age and shows some differences in respect other contemporaneous asseblages from other paleogeographical areas.

Paleoecology of sublittoral Miocene echinoids from Sardinia: A case study for substrate controls of faunal distributions

AbstractA rich echinoid fauna within the middle Miocene carbonate sedimentary succession cropping out along the coast between Santa Caterina di Pittinuri and S'Archittu (central-western Sardinia) allows the comparison of faunal gradients and preservation potentials from both hard and soft substrata. Three echinoid assemblages are recognized. Faunal composition, as well as taphonomic and sedimentological features and functional morphological interpretation of the echinoid test indicate an outer sublittoral setting. Assemblage 1 represents a highly structured environment within the photic zone, with mobile substrata occupied by infaunal irregular echinoids, mainly spatangoids, and localized hard substrata, provided by rhodolith beds, with epibenthic regular echinoids represented by the co-occurrence of the diadematidDiademaGray, 1825 and the toxopneustidsTripneustesL. Agassiz, 1841 andSchizechinusPomel, 1869. Assemblage 2 shows a higher diversity of irregular echinoids, dominated by the clypeasteroidsEchinocyamusvan Phelsum, 1774 andClypeasterLamarck, 1801 and different spatangoids, with the minute trigonocidaridGenocidarisA. Agassiz, 1869 among regular echinoids. This assemblage points to a soft-bottom environment with moderate water-energy conditions, periodically affected by storms. A low-diversity echinoid fauna in Assemblage 3, dominated by the spatangoidsBrissopsisL. Agassiz, 1840 andOvaGray, 1825, documents a deeper, soft-bottom environment, possibly below storm-wave base. These results indicate that the diversity of echinoid faunas originating in sublittoral environments is related to: (1) the presence of both soft and hard substrata, (2) differential preservation potentials of the various echinoid taxa, (3) intense bioturbation, and (4) sediment deposition by sporadic storm events.

A new Danian echinoid assemblage from the Greensand in the Kazimierz Dolny area, central Poland: taxonomy, taphonomy and sedimentological implications

We describe a new echinoid assemblage, composed of specimens of Bolbaster sp., Cyclaster danicus (Schluter, 1897), Diplodetus vistulensis (Kongiel, 1950) and Linthia ? sp. in a distinctive phosphatic preservation, from the so-called Greensand, a marly glauconitic sandstone horizon at the base of the Danian succession in the Kazimierz Dolny area (central Poland). This assemblage presumably is of early Danian age, with Cyclaster danicus occurring in the lower Danian of Denmark and southern Sweden. The specimens are preserved as internal moulds, composed of phosphatised glauconitic sandstone, occasionally with some test material adhering. The genesis of these moulds involved the following steps: (1) infilling of tests of dead echinoids with glauconitic sand; (2) penetration of the infills by coelobiotic deposit-feeding organisms that produced burrows along the inner test surface; (3) early-diagenetic cementation of infills by calcium phosphate; and (4) exhumation and intraformational reworking of specimens, leading to abrasion, fragmentation and loss of test material in some individuals. Co-occurring are unphosphatised moulds of Echinocorys ex gr. depressa (von Eichwald, 1866) and Pseudogibbaster cf. depressus (Kongiel in Kongiel and Matwiejewowna, 1937), which may represent a younger (middle to late Danian) assemblage. Additionally, the presence of derived late Maastrichtian echinoids, e.g., Temnocidaris ( Stereocidaris ) ex gr. herthae (Schluter, 1892), Pleurosalenia bonissenti (Cotteau, 1866) and Hemicara pomeranum Schluter, 1902, is confirmed for the Greensand, based on new material and re- examination of previously recorded specimens. In summary, members of three echinoid assemblages of different age and preservation occur together in the Greensand. Our results are compatible with former interpretations of this unit as a condensed, transgressive lag with mixed faunas of different age and provenance. However, they are incompatible with the hypothesis that phosphatised Danian fossils preserved in the Greensand are derived from a facies equivalent, now gone, of the lower Danian Cerithium Limestone in eastern Denmark, because all moulds are composed of phosphatised glauconitic sandstone that is utterly different from the calcareous dinocyst-dominated, fine crystalline matrix of the Cerithium Limestone.

A diverse assemblage of Permian echinoids (Echinodermata, Echinoidea) and implications for character evolution in early crown group echinoids

AbstractThe Permian is regarded as one of the most crucial intervals during echinoid evolution because crown group echinoids are first widely known from the Permian. New faunas provide important information regarding the diversity of echinoids during this significant interval as well as the morphological characterization of the earliest crown group and latest stem group echinoids. A new fauna from the Capitanian Lamar Member of the Bell Canyon Formation in the Guadalupe Mountains of West Texas comprises at least three new taxa, includingEotiaris guadalupensisThompson n. sp. an indeterminate archaeocidarid, andPronechinus? sp. All specimens represented are silicified and known from disarticulated or semiarticulated interambulacral and ambulacral plates and spines. This assemblage is one of the most diverse echinoid assemblages known from the Permian and, as such, informs the paleoecological setting in which the earliest crown group echinoids lived. This new fauna indicates that crown group echinoids occupied the same environments as stem group echinoids of the Archaeocidaridae and Proterocidaridae. Furthermore, the echinoids described herein begin to elucidate the order of character transitions that likely took place between stem group and crown group echinoids. At least one of the morphological innovations once thought to be characteristic of early crown group echinoids, crenulate tubercles, was in fact widespread in a number of stem group taxa from the Permian as well. Crenulate tubercles are reported from two taxa, and putative cidaroid style U-shaped teeth are present in the fauna. The presence of crenulate tubercles in the archaeocidarid indicates that crenulate tubercles were present in stem group echinoids, and thus the evolution of this character likely preceded the evolution of many of the synapomorphies that define the echinoid crown group.

Ecomorphological and taphonomic gradient of clypeasteroid-dominated echinoid assemblages along a mixed siliciclastic-carbonate shelf from the early Miocene of northern Sardinia, Italy

Ecomorphological and taphonomic gradient of clypeasteroid-dominated echinoid assemblages along a mixed siliciclastic-carbonate shelf from the early Miocene of northern Sardinia, Italy

Palaeoecology and taphonomy of spatangoid-dominated echinoid assemblages: A case study from the Early-Middle Miocene of Sardinia, Italy

The Early-Middle Miocene marine sedimentary succession of the Borutta Formation cropping out at Porto Torres (northern Sardinia) represents one of the most diverse and well-preserved spatangoid-dominated sedimentary successions in the Miocene of the Mediterranean area. The echinoid-bearing succession is studied with the twofold purpose of firstly reconstructing the palaeoenvironmental setting in which these echinoids occurred, and secondly investigating factors influencing the preservation potential of spatangoid echinoids in the fossil record. These goals are accomplished by 1) detailed logging of sedimentary facies, 2) applying functional morphological interpretations of echinoid skeletons in order to reconstruct their behaviour and life habits, 3) quantifying the relative abundance of taxa and taphonomic features of test preservation, and 4) analyzing associated trace fossils within the beds.The sedimentary succession is composed mainly of fine-grained sandstones which are intensely bioturbated by Thalassinoides-like burrows. Spatangoid abundance is high throughout the profile declining only in intercalated dm-thick rhodolith beds. A 20-cm-thick bed with a bedding surface of approximately 250m2 was investigated in detail with respect to relative abundance of spatangoid taxa and taphonomic signatures. The echinoids consist almost exclusively of deposit-feeding irregular forms with a dominance of the spatangoids Ova and Brissopsis and the minute clypeasteroid Echinocyamus. The spatangoids Opissaster, Holanthus, Metalia and Hemipatagus as well as the clypeasteroid Clypeaster marginatus are also present.A low energy, moderately deep, outer sublittoral environment with high rates of bioturbation and episodes of sediment deposition by storms is inferred. Interspecific competition among deposit-feeding echinoids appears to be limited by their different burrowing depths, feeding strategies and resource partitioning. The gregarious behaviour of spatangoid echinoids, their habitat in quiet, deeper environments and episodes of rapid deposition seem to represent the main factors leading to this spatangoid-bearing deposit. Since both shallow- and deep-burrowing spatangoid echinoids are well represented as complete specimens, mode of life does not appear to play a major role in their preservation potentials.

Echinoid assemblages from the early Miocene of Funtanazza (Sardinia): A tool for reconstructing depositional environments along a shelf gradient

Lower Miocene echinoid assemblages from Funtanazza, midwestern Sardinia, are studied with respect to reconstructing palaeoenvironmental conditions along a shelf gradient. This is accomplished by 1) detailed logging of sedimentary facies, 2) applying functional morphological reconstructions of echinoid skeletons and interpreting their behaviour and life habits, 3) quantifying various taphonomic features of test preservation, and 4) analysing accompanying fauna and flora.The Funtanazza section is dominated by fine- and coarse-grained siliciclastic lithologies. Eighteen genera of both regular and irregular sea urchins are recognized herein. Of these, sixteen occur in seven echinoid assemblages which were distinguished with respect to abundance, diversity, taphonomy and lithology. Littoral environments are characterized by the camarodonts Genocidaris and Psammechinus, the clypeasteroids Clypeaster and Echinocyamus, and the echinolampadoids Hypsoclypus and Echinolampas; the cidaroids Prionocidaris and Tylocidaris (Sardocidaris) and the spatangoid Spatangus are also present. Higher diversity is represented in inner sublittoral environments with the co-occurrence of the regular echinoids Prionocidaris, Tylocidaris (Sardocidaris), Tripneustes and Genocidaris and the irregular echinoids Clypeaster, Echinocyamus, Hypsoclypus, Echinolampas, Schizaster, Spatangus, Lovenia and Trachypatagus. Outer sublittoral environments are dominated by spatangoid echinoids and the cidaroid Tretocidaris (Stylocidaris).Various substrates, such as boulders and pebbles, mobile fine and coarse sediments, secondary hardgrounds and seagrass and bryozoan patches, can be inferred. Preservation style with respect to abrasion, fragmentation and encrustation can vary widely among different taxa and environments and are interpreted as a function of constructional morphology and ambient environmental factors.The echinoid assemblages of Funtanazza contain taxa which, in part, are widespread in the Miocene sedimentary successions of the circum-Mediterranean area. The described echinoids and assemblages are compared to other similar coeval occurrences and their applicability as palaeoenvironmental indices discussed.

THE ORIGIN AND PALEOECOLOGY OF CLYPEASTEROID ASSEMBLAGES FROM DIFFERENT SHELF SETTINGS OF THE MIOCENE OF SARDINIA, ITALY

Abstract Clypeasteroid echinoids can be common in both siliciclastic and carbonate sedimentary sequences of the Miocene of the Mediterranean and Paratethys areas where they frequently form highly fossiliferous deposits. Two echinoid assemblages dominated by clypeasteroids from the early-middle Miocene of Logudoro region (Northern Sardinia) are compared using a detailed sedimentological and taphonomic analysis along with functional morphological considerations. The assemblages differ widely with respect to taxonomic composition, sedimentological features, and taphonomic signatures, such as the orientation and degree of abrasion, encrustation, and bioerosion. The first assemblage (Ardara) is characterized by a low-diversity echinoid fauna, consisting exclusively of the two clypeasteroid genera, Amphiope and different morphotypes of Clypeaster. This deposit represents a proximal tempestite originating in a high-energy, shallow-water, shoreface setting. Higher diversity characterizes the second assemblage (It...

Turonian-Santonian echinoids from Wadi Qena, Eastern Desert, Egypt; a new arrangement of apical disc plating in spatangoids

Eighteen echinoid species (seven regular and eleven irregular) belonging to twelve genera have been described from the Turonian-Santonian succession of two sections located in the northern part of Wadi Qena, Eastern Desert. The diversity of the recorded species is low in the Turonian (six species), but comparatively high in the Coniacian-Santonian (twelve species). Of the recorded species, Most of these species (72%) are recorded for the first time from Wadi Qena area, one left in open nomenclature, Mecaster sp., represents a new species, and two, Phymosoma microtuberculatum and Thylechinus (T.) said, represent new records for Egypt. The taxonomic rank of Parapygus sudrensis has been changed. Phymosoma microtuberculatum which is known from the ‘Senonian’ of southwest Europe is recorded herein in the lower Turonian. Two echinoid assemblage zones are recognizable in each of the studied two sections. They are correlated with other fossil assemblage zones in Egypt. Faunal affinity and paleobiogeography of the species are discussed. A new arrangement of apical disc plating in spatangoids is described and discussed.

The origin of echinoid shell beds in siliciclastic shelf environments: three examples from the Miocene of Sardinia, Italy

Three mass accumulations of sea urchins from the Miocene of Sardinia show a number of taphonomic features which set them apart from previously described echinoid assemblages from the Cenozoic in which they represent: (1) monotypic assemblages; (2) include very well-preserved remains of either regular or spatangoid echinoids; and (3) originate in deeper water environments. These accumulations are compared using a detailed sedimentological and taphonomic analysis including preservational fabrics, taphonomic signatures, size frequency distributions, density of occurrences and preferred orientations. The possible role of gregarious behaviour contributing to mass occurrences and the specific sedimentary events leading to the excellent preservation are discussed. The interpreted depositional environment of all three deposits is that of a storm-dominated, siliciclastic shelf environment. A phymosomatid assemblage represents rapid burial through obrution of a highly dense, freshly dead community. A Brissopsis-dominated spatangoid assemblage represents a mixed accumulation of parautochthonous and transported skeletons. The third assemblage consisting of regular echinoid spines and rare tests represents a composite tempestite. Differences in the depositional environments are related to their position along onshore–offshore gradient with the first two beds originated in a deeper setting than that of the spine accumulation. This study shows that the preservation of assemblages containing complete regular echinoids and spatangoids is higher in deeper water settings than in shallow water environments.

Middle–upper Cenomanian echinoids from north Wadi Qena, North Eastern Desert, Egypt

Two Upper Cretaceous (middle–upper Cenomanian) sections located at the northern part of Wadi Qena were measured and their echinoids were collected carefully bed by bed. This area is abnormally rich in echinoids where their diversity is high and also many species are abundant. Twenty-three echinoid species (10 regular and 13 irregular) referred to twelve genera have been identified and taxonomically described. Two new species are established: Pedinopsis hemisphaerica and Phymosoma elqotti. The taxonomic rank of two species is changed. Three species, which are described from the Cenomanian of Algeria and Tunisia, are new records from Egypt. Phymosoma major Coquand, which is common in the Turonian of North Africa and south Europe, is recorded here in the Late Cenomanian for the first time. The echinoid Anorthopygus Cotteau, 1859 and its species are revised. Three echinoid assemblage zones are delineated in each of the two studied sections. They are compared to other macro-faunal assemblage zones in the Cenomanian at different parts in Egypt. The palaeobiogeography of the echinoids in the present study is discussed.

Cyclone trends constrain monsoon variability during late Oligocene sea level highstands (Kachchh Basin, NW India)

Abstract. Climate change has an unknown impact on tropical cyclones and the Asian monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin) as a recorder of tropical cyclone activity along the NW Indian coast during the late Oligocene warming period (~ 27–24 Ma). Proxy data providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system at the Oligocene–Miocene boundary. The vast shell concentrations are comprised of a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deeper to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished, each recording a relative storm wave base. (1) A shallow storm wave base is shown by nearshore molluscs, reef corals and Clypeaster echinoids; (2) an intermediate storm wave base depth is indicated by lepidocyclinid foraminifers, Eupatagus echinoids and corallinacean algae; and (3) a deep storm wave base is represented by an Amussiopecten bivalve-Schizaster echinoid assemblage. These wave base depth estimates were used for the reconstruction of long-term tropical storm intensity during the late Oligocene. The development and intensification of cyclones over the recent Arabian Sea is primarily limited by the atmospheric monsoon circulation and strength of the associated vertical wind shear. Therefore, since the topographic boundary conditions for the Indian monsoon already existed in the late Oligocene, the reconstructed long-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~ 26 Ma followed by a period of monsoon weakening during the peak of the late Oligocene global warming (~ 24 Ma).

Environmental control on the structure of echinoid assemblages in the Bellingshausen Sea (Antarctica)

The Bellingshausen Sea is one of the most remote and least surveyed seas of the Southern Ocean, so that little was known about benthic communities and those factors that determine community structuring until recently. The present work aims at characterizing the structure and spatial distribution of echinoid assemblages in the Bellingshausen Sea, as well as identifying the environmental factors that determine assemblage structuring. Echinoids were collected at 32 stations using an Agassiz trawl, at depths of 86–3,304 m, during BENTART oceanographic expeditions led in 2003 and 2006. Sediment and bottom water properties were analysed using an USNEL-type box corer and a Neil Brown Instrument System Mark III CTD, respectively. Echinoids were found at all stations, except Peter I Island. Seventeen species were identified, representing 22 % of the echinoid species present in the Southern Ocean and increasing twofold the number of species recorded in the Bellingshausen Sea so far. The echinoid fauna is dominated by the very abundant species Sterechinus antarcticus. Depth is the key factor that determines the nature of echinoid assemblages, which are mainly divided into the continental shelf, the slope and the deep-sea basin. In addition, sediment properties, namely redox values, organic matter and mud content, best match species dispersion on the shelf. Sediment properties affect echinoid distribution depending on species food range and feeding strategy. As it might be expected, sediment properties more strongly influence specialist feeders (Schizasteridae and Cidaridae) than generalists (Echinidae).

Tithonia oxfordiana, a new irregular echinoid associated with Jurassic seep deposits in south‐east France

Abstract: The infaunal irregular echinoid, Tithonia oxfordiana, is described and compared to congeneric species previously described from Upper Jurassic and lowermost Cretaceous strata. This new species characterizes a monospecific echinoid assemblage, which occurs only in some places where deep‐marine middle Oxfordian deposits are exposed in south‐east France. Specimens are closely packed and clearly concentrated at the top of small carbonate chemoherms; a close connection of the echinoids with the emission of reduced chemicals, which were oxidized by chemoautotrophic bacteria, is highly probable. Based on general test shape and plate architecture, T. oxfordiana probably was a deposit feeder on chemosynthetic organic matter produced by such bacteria. In view of the fact that T. oxfordiana is the sole species of the Jurassic genus Tithonia known from Oxfordian strata, it is postulated that chemoherms possibly acted as refugia for these peculiar echinoids, which have an episodic record between the Callovian and Valanginian.

The pre-Messinian deep-sea Neogene echinoid fauna of the Mediterranean: Surface productivity controls and biogeographical relationships

Autochthonous deep-water echinoid faunas are very rare in the fossil record. A well-preserved bathyal echinoid assemblage is described from the middle Miocene Pakhna Formation of southern Cyprus. This low-diversity fauna is dominated by just two genera of spatangoid ( Palaeobrissus and Heteropneustes), and implies a water depth of 200–1000 m. Echinoids occur in modest abundance but are restricted to a small number of intervals where sapropels are numerous and thick, although never in the sapropels themselves. This suggests that echinoids in the deep pre-Messinian Mediterranean were surviving at depth by exploiting raised levels of nutrient input driven by Milankovitch forcing, but being excluded at times of peak carbon settlement. In contrast to the modern depauperated deep-water fauna of the Mediterranean, which has Atlantic affinities, these two species show strongest phylogenetic affinities with bathyal Caribbean fauna. Caribbean and Mediterranean deep-sea macrobenthic faunas were thus closely connected until just before the Gibraltar Sill formed.