Ostracod Carapace Research Articles

Palaeontological and taphonomical investigations of the exceptionally rich concentration of Miocene vertebrate coprolites from Pécs-Danitzpuszta (Hungary, Mecsek Mts.)

ABSTRACT Thousands of coprolites have been collected from the Upper Miocene (Tortonian/Pannonian) sands of the Pécs-Danitzpuszta sand pit, one of the most important mixed Neogene vertebrate localities in Hungary. Although, the locality has been known for centuries, the coprolites have not been investigated in detail. We describe these fossils and explore their palaeoecological significance. Coprolites were examined with thin sections, X-ray powder diffraction and computed tomography. Their surface is mostly smooth, desiccation cracks were not observed. All coprolites mainly consist of apatite, indicating most probably a carnivorous diet. No evidence of herbivory has been found so far. The coprolites contain remains belonging to several groups: ostracod carapaces, bivalve shells, vertebrae from bony fishes, fish scales, as well as teeth. The CT scans show inhomogeneities in the matrix; however, in most cases they do not reliably indicate inclusions. The taphonomical features suggest rapid burial and most likely an aquatic origin. The spiral morphotype could be attributed to fishes with spiral intestinal valves. Teeth of reef-associated fish taxa indicate Badenian age for some specimens, though the coprolite assemblage might include older and younger specimens as well.

Pyrite-bearing non-marine ostracods from the Lower Cretaceous Maracangalha Formation, Recôncavo Basin, NE Brazil: Depositional controls and paleoecological implications

Ostracods are aquatic microcrustaceans which use calcium dissolved in water to synthesize their carapaces, along with a low magnesium content. Depending on the conditions of the depositional environment and diagenetic processes, ostracods can be preserved in the fossil record, with or without alteration of the original chemical composition. In this study, samples from shales, siltstones and silty sandstones of the Maracangalha Formation (Recôncavo Basin) along the Gameleira and Manguinhos (Ilha de Itaparica) and Praia da Falha (Ilha dos Frades) outcrops, Baía de Todos os Santos, were analyzed. Results show that the pattern of ostracod carapaces preservation was controlled by distinct sedimentological processes. In the Manguinhos and Praia da Falha outcrops, ostracod specimens show total or partial replacement of the carapace by pyrite, with the more expressive pyritization observed in shale from Manguinhos. In the Gameleira outcrop, on the other hand, no pyritized carapaces were observed. Results of the Energy Dispersive Spectrometry (EDS) from Manguinhos and Praia da Falha outcrops indicate the presence of Fe and S pointing to pyrite mineralization. The Scanning Electron Microscopy (SEM) images revealed the euhedral and framboidal habit of pyrites present in the carapaces. The low recovery of specimens from Gameleira and Praia da Falha, as well as the abundance of specimens in Manguinhos, seem to have depositional controls. At Gameleira and at Praia da Falha, facies associated with low-to-high density turbidity currents may have hampered preservation, thus low recovery of ostracods. Despite the occurrence of fragmented carapaces, the anoxic conditions of the Manguinhos shale samples allowed a better preservation of specimens. The Manguinhos facies are interpreted as relatively deep lacustrine deposits. The presence of framboidal pyrite suggests early conditions of diagenesis at low burial depths. Pyrite mineralization may have occurred through a hydrogen sulfide environment, rich in organic matter, with dissolution of the carbonate carapace through the acidic pH of the medium and relative rapid post-mortem burial. The sedimentary facies described, along with the taphonomic results of ostracod preservation, corroborate a lacustrine environment with occasional sediment gravity flows to the Maracangalha Formation.

Paleothermometric Inferences Using Elemental Mapping: An Appraisal of Ostracoda Species from Shallow Core Sediment of Bay of Bengal, India

Elemental mapping of Ostracoda valves to infer the paleothermometric fluctuations from off-Visakhapatnam, Bay of Bengal is the focus of the present paper. Two Ostracoda species such as Bairdoppilata (Bairdoppilata) alcyonicola and Actinocythereis scutigera were dominant throughout the core. The weight percentages of Mg, Sr, Ba, Fe and Mn in ostracod carapaces were estimated and the ratio with respect to Ca was analyzed to decipher the paleoclimate and oxy-redox conditions. It is observed that trace element accumulation varies with respect to different ostracod species and shell position. Thus, the elemental mapping of the ostracod carapaces by the EDS techniques proved as a primary proxy to decipher the paleotemperature fluctuations in the study area. Keywords: Paleothermometry, Elemental Mapping, Ostracoda, Visakhapatnam, Bay of Bengal

Qualitative and quantitative analyses of the Carboniferous ostracod genus Carbonita from Rod El-Hamal area, Wadi Araba, north Eastern Desert, Egypt

ABSTRACT The present work provides a qualitative analysis of the studied ostracod carapaces of the genus Carbonita. Thirty-seven ostracod specimens were collected from the Late Carboniferous Rod El-Hamal Formation at Rod El-Hamal area, Wadi Araba, north Eastern Desert, Egypt. The collected ostracods were assigned to four species in genus Carbonita; C. fabulina (Jones and Kirkby), C. inflata (Jones and Kirkby), C. humilis (Jones and Kirkby), and C. bairdoides (Jones and Kirkby) according to the qualitative traits. In order to assess the discrimination among the different Carbonita species, a new technique, geometric morphometric analyses, was carried out using ImageJ and MorphoJ software packages. Geometric morphometric analyses included landmark configurations, procrustes superimposition, principle component analysis, and thin plate spline deformation plots. Using nine landmarks, average shapes of the different Carbonita species have been provided. The principle component analysis separated Carbonita fabulina and C. bairdoides from the morphologically overlapped C. inflata and C. humilis. Shape variations in the carapace length, height, anteroventral arc, posterodorsal arc, posteroventral arc, and the anterior margin were demonstrated through the deformation plots. These quantitative analyses, along with the qualitative examination, provided considerable variations among the different Carbonita species, and hence the best way for species discrimination.

The ultrastructural development and 3D reconstruction of the transparent carapace of the ostracod Skogsbergia lerneri

The Skogsbergia lerneri is a marine ostracod which possesses a carapace that is both protective and transparent. Since development of this carapace and how it is maintained in the adult is not known, the aim of this investigation was to carry out an in-depth ultrastructural study of the ostracod carapace at different developmental stages. Standard transmission electron microscopy and novel serial block face scanning electron microscopy (SBF-SEM) were undertaken to discern carapace ultrastructure in both two and three dimensions. Analysis revealed a carapace consisting of the same basic layer structure as other myodocopid ostracods, namely an epicuticle, exocuticle, endocuticle and membranous layer, but with a thinner adult carapace of mean thickness of 19.2 ± 1.78 µm, n = 5. The carapace layers, except for instar 1 ostracods, had similar relative proportions throughout development. The endocuticle and membranous layer thickened through advancing developmental stages due to an increase in calcified crystalline polyhedrons and a greater number of chitinous lamellae in the membranous layer. Crystalline polyhedron dimensions were significantly smaller near the boundary with the membranous layer. The borders between the carapace layers were indistinct; SBF-SEM revealed an abundance of epicuticle projections into the exocuticle and apparent gradual merging at the boundary of the exocuticle and the endocuticle. Here, we discuss how the S. lerneri carapace layer structure has evolved to serve a specific mechanical function, allowing surface protection and rigidity. In addition, we suggest that the lack of pigment and graduated layer boundaries contribute to the transparency of the carapace.

First usage of ostracod species (Herpetocypris brevicaudata) carapace as a biosorbent with XAD-4 resin to determine Co(II), Cu(II) and Mn(II) trace metal ions

Powdered ostracod carapace of the species (Herpetocypris brevicaudata), an invertebrate aquatic crustacean, loaded on Amberlite XAD-4 resin, were tested as a biosorbent to determine concentrations of trace metal ions (Cu(II), Co(II), Mn(II)) in water samples prior to UV–VIS spectrophotometric analyses. Effects of sample pH, volume, type and volume of eluent, matrix interference, and flow rate of sample and eluent were examined to investigate optimum biosorption conditions of the trace metal ions.Optimum pH values for Cu(II), Co(II) and Mn(II) were around 10.0. Metals were desorbed with 1 M HCl (recovery, 90–100% and high precision; SD < 5%). Sorption capacity of AXAD-4 resin loaded with H. brevicaudata was 0.71, 0.23 and 0.64 mmol g−1 for Cu(II), Co(II) and Mn(II), respectively.Performances of the new sorbent were evaluated using certified reference material (TMDA-70.2 Ontario Lake Water).

Biomimetic Transparent Eye Protection Inspired by the Carapace of an Ostracod (Crustacea)

In this study we mimic the unique, transparent protective carapace (shell) of myodocopid ostracods, through which their compound eyes see, to demonstrate that the carapace ultrastructure also provides functions of strength and protection for a relatively thin structure. The bulk ultrastructure of the transparent window in the carapace of the relatively large, pelagic cypridinid (Myodocopida) Macrocypridina castanea was mimicked using the thin film deposition of dielectric materials to create a transparent, 15 bi-layer material. This biomimetic material was subjected to the natural forces withstood by the ostracod carapace in situ, including scratching by captured prey and strikes by water-borne particles. The biomimetic material was then tested in terms of its extrinsic (hardness value) and intrinsic (elastic modulus) response to indentation along with its scratch resistance. The performance of the biomimetic material was compared with that of a commonly used, anti-scratch resistant lens and polycarbonate that is typically used in the field of transparent armoury. The biomimetic material showed the best scratch resistant performance, and significantly greater hardness and elastic modulus values. The ability of biomimetic material to revert back to its original form (post loading), along with its scratch resistant qualities, offers potential for biomimetic eye protection coating that could enhance material currently in use.

Establishment of long-term ostracod epidermal culture

Primary crustacean cell culture was introduced in the 1960s, but to date limited cell lines have been established. Skogsbergia lerneri is a myodocopid ostracod, which has a body enclosed within a thin, durable, transparent bivalved carapace, through which the eye can see. The epidermal layer lines the inner surface of the carapace and is responsible for carapace synthesis. The purpose of the present study was to develop an in vitro epidermal tissue and cell culture method for S. lerneri. First, an optimal environment for the viability of this epidermal tissue was ascertained, while maintaining its cell proliferative capacity. Next, a microdissection technique to remove the epidermal layer for explant culture was established and finally, a cell dissociation method for epidermal cell culture was determined. Maintenance of sterility, cell viability and proliferation were key throughout these processes. This novel approach for viable S. lerneri epidermal tissue and cell culture augments our understanding of crustacean cell biology and the complex biosynthesis of the ostracod carapace. In addition, these techniques have great potential in the fields of biomaterial manufacture, the military and fisheries, for example, in vitro toxicity testing.

Utilization of Ostracods (Crustacea) as Bioindicator for Environmental Pollutants

Ecosystem undergoes drastic changes due to the anthropogenic activities. As a consequence of industrial development, increasing population growth and modernized agricultural practices water resources like limnetic zone and marine areas have undergone eutrophication. This resulted in the decline in population of phytoplankton and zooplankton. Hence, it is an urgent need to monitor the quality of the environment. Several organisms are used as biomonitors. Among them, Ostracodes (Seed Shrimps) which belong to Crustacean group are very sensitive to those changes in the environment and useful in predicting the paleo environmental conditions. Ostracodes are bivalve arthropods which are enclosed in a carapace made of low magnesium calcite. These species are occurring for about 450 million years dates back to ordovician which are known for their easier fossilization. The development of Ostracodes is influenced by the physic - chemical properties of waters such as Salinity, temperature, pH, Dissolved oxygen, bottom grain sizes and sedimentation rates. In addition to diversity and abundance of population, morphological and geochemical changes can also be detected in the Ostracod carapace (shell) which serves as a tracer of the water quality. These details are basis for utilizing Ostracods as paleoenvironmental (paleoclimatic, paleosalinity, paleooceanographic) reconstruction, ecotoxicity monitoring, biostratigraphic indicator. Moreover, these microcrustaceans showed similar or higher sensitivity to herbicides, pesticides, oil spills or heavy metals pollution other than traditional groups like copepods, protozoan, rotifers, cladocerans which are used to test the human impacts on ecosystem. These meiofaunas are highly adaptable to waters containing organic and inorganic contaminants generated by catastrophic activities by human beings in the surroundings.

UNUSUAL FOSSILIFEROUS CONCRETIONS FROM LACUSTRINE DEPOSITS IN THE LOWER JURASSIC MOENAVE FORMATION IN ST. GEORGE, UTAH, USA: IMPLICATIONS FOR ANCIENT FISH MASS MORTALITIES

ABSTRACT Two types of unusual concretions with similar biotic contents but markedly different shapes and distributions were found in close stratigraphic proximity within the Lower Jurassic Whitmore Point Member of the Moenave Formation in St. George, Utah. Both types of concretions formed in lacustrine sediments and contain abundant ganoid fish scales, numerous ostracode carapaces, and apparent rip-up clasts. Elongate, cylindrical concretions developed in parallel and regularly spaced rows in one horizon, and comparatively flat and irregularly shaped and distributed concretions formed in an overlying layer only a few centimeters above. Microprobe and Raman analyses of concretion samples reveal abundant hematite in both concretions as well as groundmass minerals dominated by silica in the cylindrical concretions and dolomite in the flat concretions. The abundance of fish skeletal debris in concretions from two consecutive horizons may suggest recurring fish mass mortality in ancient Lake Dixie, the large lake that occupied the St. George area during the Early Jurassic. We propose a model for the formation of the concretions based on their shapes, distributions, and chemistry. In this model, accumulations of disarticulated fish debris were colonized and consolidated by microbial mats and shaped by oscillatory flow (in the case of the cylindrical concretions) or lack thereof (in the case of the flat concretions). Then, after burial, groundwater chemistry and possibly the metabolic activities of microorganisms led to the precipitation of minerals around and within the masses of fish material. Finally, diagenetic alteration changed the mineral makeups of the cylindrical and flat concretions into what they are today.

Molluscs and Ostracods of the Qarun Lake: Preliminary Report From FA-1 Core in Faiyum Oasis, Northern Egypt

Abstract A research was conducted on the Holocene lake sediments from the full-cored FA-1 drilling at the southern shore of the Qarun Lake in the Faiyum Oasis in northern Egypt. Altogether 10 taxa of molluscs and 8 taxa of ostracods were identified in the examined deposits, with total amounts of 768 and 2872 individuals, respectively. The fauna was investigated with palaeoecological purpose and allowed for preliminary reconstruction of sedimentary environment in the lake. The occurrence of Valvata nilotica Jickeli, 1874 and Gomphocythere sp. in the lower part of the core and a low proportion of carapaces (2.4-28%) indicated freshwater and higher-energy conditions, respectively. Rapid expansion of Cyprideis torosa (Jones, 1850) at a depth of 18 m could point to very short saline episode in the lake. The increase in salinity and drop of water level were evidenced in the uppermost part of the core (4-3.5 m), when the lake was dominated by Hydrobia ventrosa (Montagu, 1803), Cerastoderma glaucum (Poiret, 1789) and C. torosa. The steady sedimentation in a shallow lake was also supported by considerable amount of complete ostracod carapaces (45%). The faunal assemblage and smooth valves of C. torosa suggested salinity of 14-25‰.

Middle Miocene ostracods from Wadi Sudr, westcentral Sinai, Egypt: systematic, biostratigraphy and palaeobiogeographic affinity with the Mediterranean realm

The investigation of the exposed middle Miocene strata from Wadi Sudr yielded well-preserved ostracod carapaces. Detailed taxonomic and paleontological studies led to the recognition of 36 ostracod species belonging to 25 genera, 4 species of them were considered new which fully described. Three assemblage biozones were recorded as follows: Actinocythereis spinosa–Actinocythereis hystrix zone, Chrysocythere cataphracta muricata-Cytheretta africana zone, and Disopontocypris schweijeri-Bythocypris tripolensis zone. The recorded biozones were calibrated with the previously studied middle Miocene planktonic foraminiferal biozones on the same samples and also correlated with the Miocene ostracod biozones from the neighboring countries. Our ostracod assemblages present in the lower and upper parts of the studied section (section II) indicated an inner neritic marine environment of moderate energy of currents and rapid sedimentation, while the assemblages in the middle part showed more deeper (outer neritic) environments with low energy of currents and low rate of sedimentation. The palaeobiogeographic distribution of the studied ostracods showed high affinity with the ostracod assemblages of the southern Mediterranean and moderate to low affinities with that of the northern and eastern Mediterranean respectively. The highly ornamented ostracod species with structures on the carapace were recorded from both Northern and Southern Mediterranean, while the smooth ones were found in the Southern Mediterranean only. The highly ornamented species are more widely distributed in both Southern and Northern Mediterranean than the smooth species. This may indicate that the ornamented species are more able to migrate than the smooth ones.

Insight into tube-building behaviour and palaeoecology of some agglutinating worms from the Upper Devonian of Nevada, USA

Agglutinated worm tubes from the Upper Devonian of the Devils Gate section in Nevada, USA are reported for the first time, filling a major gap in their Palaeozoic fossil record. Two small (5mm and 6.7mm in length) tubes are composed entirely of tentaculitid shells, and one large tube (55mm in length) is formed from particles including ostracode carapaces, echinoderm ossicles, tentaculitid shells and putative bryozoan fragments aligned perpendicularly to the tube's long axis. The tubes, in particular the large one have a cylindrical, curved and tapering tube morphology that is very similar to that of modern agglutinating polychaetes of the families Terebellidae and Pectinariidae. The large tube is dominated by objects that fall within a certain size-range, and although built from different types of particles, echinoderm ossicles are prevalent in the posterior part, whereas ostracode carapaces dominate in the middle and anterior parts of the tube. Tentaculitid shells are relatively rare in the large tube, despite being abundant in the surrounding host deposit. The faunal assemblage composing the tube suggests that the worm animal was rather specific in its selection of particles with a certain morphology. This is common behaviour amongst many modern agglutinating terebellid and pectinariid polychaetes. The preservation of such fragile tubes was enhanced by rapid burial, likely caused by gravity flow of sediment in a deep-slope setting.

Ostracods: The ultimate survivors

Ostracods are tiny crustacean arthropods just a few millimetres long, with a bivalved carapace made of calcium carbonate that covers the whole body, and into which the animal can retreat from the world outside. Because of their diminutive size they are largely overlooked as fossils, but they have a fascinating history. Silent witnesses to life in the seas since the time of trilobites, they have a fossil record extending back to the Early Ordovician, and possibly the Cambrian. Ostracods have survived nearly 500 million years of Earth history including the ‘big five’ mass extinctions of the Phanerozoic Eon; they are true survivors. They are almost perfectly adapted for the aquatic environments in which they live, and can be found from the ocean abyssal plains to damp leaf litter. The ostracod carapace is a triumph of biological engineering that has been re‐configured into myriad different morphologies according to environment. Streamlined and agile species plough through the ocean water column, sometimes reaching a ‘giant’ size of a centimetre in length, whilst their tinier sea bottom cousins make elaborately ornamented carapaces to withstand the pressures of living at the seabed, or shape their carapaces into forms that facilitate burrowing into sediment. Ostracods are key components of aquatic ecosystems. As primary consumers they are food for larger animals both in seabed and planktonic habitats, and they recycle much of the organic detritus produced by larger animals and plants. Delve into the history of ostracods and it is possible to find pioneers who triumphed in the plankton, early colonisers of terrestrial aquatic ecosystems, and ostracods that literally conquered the land. And in more recent times, ostracods have even hitched rides on rockets into space.

Analysis of marrow cavity fillings as a tool to recognise diverse taphonomic histories of fossil reptile bones: Implications for the genesis of the Lower Muschelkalk marine bone-bearing bed (Middle Triassic, Żyglin, S Poland)

Abstract The bone-bearing bed from Żyglin (S Poland), which likely represents the oldest Lower Muschelkalk accumulation of reptile remains in the SE part of the Germanic Basin, has been investigated in order to determine its genesis. The basic methods were supported by petrographic analysis of the marrow cavity and large inter-trabecular pore space fillings of fossil bones, which was used to check its usefulness to identify the environments where the bones were initially deposited and to decipher taphonomic histories of the remains. The bone-bearing bed is a composite deposit, which consists of three distinct layers (from bottom to top): micritic limestone (mudstone, bioturbated autochthonous mud), crinoidal limestone (grainstone to packstone, calcirudite), and shell-rich limestone (packstone to wackstone, calcirudite). The crinoidal limestone layer, the main bone-bearing bed, is recognised as the proximal tempestite deposited in the mid-ramp zone. The petrographic analysis of the fillings reveals the prevalence of minute ostracod carapaces, accompanied by other grains, embedded together with micrite to microspar. Such compositions suggest that these sediments may have been inserted into the bone pore spaces in lagoons and tidal-flat ponds. Features of some bones record their early diagenetic burial and lithification before the final redeposition. The isopachous spar, blocky spar and weathered pyrite document changes in the chemical composition of fluids that flowed into the bone interiors. The burrow found in the marrow cavity of specimen IGUAM-ZOV-7 provides evidence that some remains were inhabited by minute or juvenile invertebrates. All recognised features indicate that both invertebrate and vertebrate bioclasts, included in the tempestite, were initially deposited in various settings of the carbonate ramp and in the end redeposited as a result of a heavy storm or a hurricane. The examined bone-bearing bed represents time-averaged assemblage, which originated due to hydraulic concentration of the vertebrate bioclasts. The petrographic analysis of the fillings is a valuable tool to identify complex taphonomic pathways of vertebrate bioclasts.

Oxygen isotope analysis of multiple, single ostracod valves as a proxy for combined variability in seasonal temperature and lake water oxygen isotopes

Paleoclimate studies in lakes typically use oxygen isotopic ratios in samples that consist of multiple ostracod specimens, to obtain an average δ18O value that reflects the mean temperature and δ18O of lake water over the life spans of the combined individuals measured. This approach overlooks potential information on seasonal climate variability that is recorded in the single valves of short-lived ostracods. Here we estimate seasonal variability in ostracod δ18O by measuring 10–30 individual carapaces of Cyprideis torosa in selected stratigraphic levels of a sediment core from paleolake Riwasa in Haryana, India. The mean δ18O values of ostracod populations show a general decrease from 9.6 to 8.3 kyr BP, which was interpreted previously as resulting from strengthening of the Indian summer monsoon during the early Holocene. The δ18O measurements of single ostracods within samples show a large range (up to ~15 ‰) and standard deviation (up to ±3.3), suggesting high seasonal variability in the hydrology of this playa lake. The great variability is ascribed to changes in both seasonal temperature (16 °C) and δ18O of lake water in a drying water body. The latter is attributable to the Rayleigh distillation process, described using a Craig–Gordon model for isotopic fractionation during evaporation from an open water body. Our results suggest that the range of δ18O values measured in single ostracod carapaces is useful to evaluate seasonal changes in lake temperature and hydrology. Even with great intra-sample δ18O variability, however, the mean δ18O of multiple (more than 10) ostracods can be used to infer long-term climate trends.

A TESTATE RHIZOPOD ASSEMBLAGE IN AN EXTREME ENVIRONMENT: THE ANTARCTIC PERMANENTLY ICE-COVERED LAKE HOARE (TAYLOR VALLEY)

The McMurdo Dry Valleys comprise the largest relatively ice-free area in Antarctica and are characterized by low precipitation rates. Perennial ice cover on the dry valley lakes decreases the amount of solar radiation reaching the water column, thereby reducing the interaction between the atmosphere and the water column. However, the ice partly shelters the lake ecosystems from the harsh Antarctic climate. Two cores, collected from Lake Hoare in the Taylor Valley in 1995, contained testate rhizopods (mostly Arcella ) that have only chitinous organic tests with no agglutinated material, unlike other testate rhizopods that use detrital material to build a test. Additionally, a limited number of possible ostracod carapaces and possible rotifer resting-stage remains were present. The testate rhizopod concentration is generally higher in layers containing abundant bacterial/algal-mat fragments. This reflects the local sedimentation pattern in which layers of alternating mat growth and sediment accumulation on the ice surface subsequently fall to the lake bottom.

Lower triassic (Olenekian) microfauna from Jadar block (Gucevo mt., Nw serbia)

Systematic study of microfossil associations on the Krivi Potok section (Gucevo Mt. area, NW Serbia) has been carried out to document and to refine the Lower Triassic stratigraphic correlations within Alpine-Mediterranean domain. Field investigation and laboratory process have enabled the identification of lowermost Olenekian (lower Smithian) conodonts, ostracodes and pyrite framboids. Two conodont zones are established in this region, in ascending order they are: Pachycladina obliqua-Foliella gardenae Assemblage Zone and Neospathodus planus Zone. A new ostracode species Paracypris ? krivipotokensis FOREL n. sp. has been described, it co-occurs with conodont Neospathodus planus within the Zone of the same name. The pyrite framboids were formed within the ostracode carapaces after their death. The size distribution of pyrite framboids supports the former suggestion that large size (&gt;6 ?m in diameter) is not suitable for the reconstruction of seawater redox conditions.

Tracking paleoecological and isotopic changes through the K-Pg boundary from marine ostracodes: The Poty quarry section, northeastern Brazil

Ostracode assemblages of the Poty quarry, Pernambuco-Paraíba Basin, northeastern Brazil, record an abrupt faunal change near the Cretaceous-Paleogene (K-Pg) boundary. Paleoecological and stable isotope analyses of ostracode carapaces were used to interpret the paleoenvironmental changes that took place from the Late Maastrichtian to the Early Danian. Ostracode distribution demonstrates substantial changes at and around the boundary with the last occurrences of most species and appearance of new ones. Stable isotope analyses carried out for four ostracode species distributed along the entire succession exhibit oscillations in the isotopic composition before the K-Pg boundary, thus suggesting that environmental changes may have begun slightly prior the boundary event itself. These changes may have triggered the extinctions that culminated at the K-Pg boundary, marked by positive δ18O and negative δ13C excursions. The K-Pg boundary is marked by cooling of bottom seawaters and a decrease in productivity, as well as the beginning of an extensive marine regression.

Ecophenotypic variation of the Devonian benthic ostracod species Cavellina rhenana Krömmelbein, 1954: A paleoenvironmental proxy for the Ardenne (France–Belgium) and Rheno-Hercynian realm

The morphological variation of the carapace of the ostracod species Cavellina rhenana Krömmelbein, 1954 is explored here quantitatively. This species existed during the Late Givetian to the earliest Frasnian and it is characteristic of the Rheno-Hercynian area. Five morphological characters and several linear measurements of the carapace were analyzed on 260 complete carapaces coming from three different areas, each of them representing a different paleoenvironment of the Devonian Ardennean platform. The original species description and diagnosis are emended based on this newly observed variability in ornamentation, sulcation, curvature of the ventral margin, marginal flattening and asymmetry of valves. It is established herein that the morphological variation expressed in these five characters is independent of the ontogenetic growth. Morphological variation appears to be correlated with different types of facies, reflecting a distinct depositional environment. A high degree of morphological variation is found in facies of inner platform (semi-restricted) environments, while a low degree of variation is found in facies of outer platform (open-marine) environments. Thus, the degree of morphological variation of C. rhenana is an indicator of the stability of the environment in the neritic realm. While environmentally-cued polymorphism is well documented in Mesozoic to Recent ostracods, our study demonstrates the first Devonian case of ecomorphism and suggests that intraspecific polymorphism of the ostracod carapace can be a useful tool for refining paleoenvironmental reconstructions.