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"Ostracoda"
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A comment on Lai et al. (2014) concerning the origin of the Shell Bar section from the Qaidam Basin, NE Tibetan Plateau: lake formation versus river channel deposit, and super(14)C versus OSL dates
Without understanding the true meaning of why it is called Shell Bar, and ignoring the unreliability of OSL dating and the data of Fan (2009), Lai et al. (J Paleolimnol 51:197-210, 2014) concluded that the upper part of the Shell Bar section from Qaidam Basin, which they call the SB section, was formed during MIS5 (~113-99 ka). This is at odds with Zhang et al. (Quat Sci 27:427-436, 2007a, Radiocarbon 50:255-265, 2008b) who argued that the whole 260-cm section accumulated between ~39.7 and ~17.5 super(14)C ka BP. Using grain-size data and ostracod assemblages, they further asserted that the elevated sediments of the Shell Bar were stream deposits (Mischke et al. in J Paleolimnol 51:179-195, 2014) and support their conclusion using a nearby section they call the SSB section. This section, we believe, is old, fluvial-alluvial and shallow-water sediments, interbedded with eolian deposits, and its cliff-like appearance can be attributed to backward erosion processes during a high-water stand. All the OSL measurements used to date the section were produced at one laboratory, and the results are at odds with their conclusions. It is impossible for Lai et al. (J Paleolimnol 51:197-210, 2014) to ignore the AMS super(14)C dates and rely fully on their OSL ages, which are not constrained or verified by other dating techniques. For the sedimentation and geomorphologic processes to be fully understood, we must have a solid understanding of the paleoclimatic and paleoenvironmental changes, and paleolake evolution, reconstructed using lake deposits, geomorphologic features, microfossil and macrofossils, pollen and other environmental variables.
Journal Article
Foraminifer and Ostracod Occurrence in a Cool-Water Carbonate Factory of the Cape Adare
Foraminifers and ostracods were studied in a gravity-core recovered near Cape Adare (Ross Sea, Antarctica) with the aim of identifying the climatic and oceanographic variations during the last 30 ka. The sedimentary sequence represents conditions of a cool-water carbonate factory, which evidences that during the Marine Isotope Stage 2 (MIS2) the area was ice-free and very productive. The overall preservation of delicate skeletal remains such as bryozoans and molluscs indicated moderate bottom currents. This carbonate factory was interrupted by some terrigenous levels, representing conditions of instability/retreat of the ice shelves southward. The younger levels were referred to the meltwater pulse (MWP)-IA and IB events. The Holocene sequence comprised more terrigenous sediments, reflecting high bottom-currents similar to the present-day conditions. Very abundant and well preserved foraminifers and ostracods, representative of shelf-upper slope paleoenvironments, were recovered. Epistominella exigua, among the foraminifers, suggested the influence of the Circumpolar Deep Water during some periods of the late Quaternary. Heavy-test taxa, such as Cibicides reflilgens, indicated strengthening bottom hydrodynamics. As for the ostracods, peaks in the presence of Australicythere devexa, Bairdoppilata simplex and Pseudocythere aff. caudata together with significant values of Polycope spp. allowed us to identify environments rich in nutrients with the influence of cold and deep water upwelling phenomena.
Journal Article
Stable carbon isotopes ( delta super(13)C) of total organic carbon and long-chain n-alkanes as proxies for climate and environmental change in a sediment core from Lake Peten-Itza, Guatemala
Sediment core PI-6 from Lake Peten Itza, Guatemala, possesses an ~85-ka record of climate and environmental change from lowland Central America. Variations in sediment lithology suggest large and abrupt changes in precipitation during the last glacial and deglacial periods, and into the early Holocene. We measured stable carbon isotope ratios of total organic carbon and long-chain n-alkanes from the core, the latter representing a largely allochthonous (terrestrial) source of organic matter, to reveal past shifts in the relative proportion of C sub(3)-C sub(4) terrestrial biomass. We sought to test whether stable carbon isotope results were consistent with other paleoclimate proxies measured in the PI-6 core, and if extraction and isotope analysis of n-alkanes is warranted. The largest delta super(13)C variations are associated with Heinrich Events. Carbon isotope values in sediments deposited during the last glacial maximum indicate moderate precipitation with little fluctuation. The deglacial was a period of pronounced climate variability, e.g. a relatively warm and moist Boelling-Alleroed, but a cool and dry Younger Dryas. Arid periods of the deglacial were inferred from samples with high delta super(13)C values in total organic carbon, which reflect times of greater proportions of C sub(4) plants. These inferences are supported by stable isotope measurements on ostracod shells and relative abundance of grass pollen from the same depths in core PI-6. Similar trends in carbon stable isotopes measured on bulk organic carbon and n-alkanes suggest that carbon isotope measures on bulk organic carbon in sediments from this lake are sufficient to infer past climate-driven shifts in local vegetation.
Journal Article
On Caledromusrobinsmithi , a new genus and species of Psychrodromini Martens, 2001 (Crustacea, Ostracoda, Herpetocypridinae) from New Caledonia (Pacific Ocean)
The New Caledonian Archipelago is a hot spot for biodiversity and endemism. Whereas popular groups such as birds and plants are well-studied, invertebrate groups such as ostracods remain ill-known. Here,
is described from a single locality on 'Grande Terre', the main island of the archipelago. The new genus belongs to the Psychrodromini, one of the four tribes in the subfamily Herpetocypridinae (family Cyprididae).
can be distinguished from all other herpetocypridinids by a combination of the following factors: the absence of marginal septa in both valves, the mildly developed marginal valve structures, the small Rome organ on the A1, the total reduction of the five natatory setae on the A2, the rectangular second palp segment of the Mx1, the broad and asymmetrical palp on the female T1, the absence of additional postlabyrinthal coils in the Hp and the seta Sp of the CR which is a fixed spine. Because of the close similarity to the genus
, the new genus is thought to have Palaearctic affinities, contrary to other ostracod species in New Caledonia, which are either circumtropical or with Australian zoogeographical connections.
Journal Article
On Cytheridella whitmani sp. nov. , with a reappraisal of the taxonomy of the genus
Cytheridella whitmani Martens, sp. nov. is described from lakes on Cape Cod (MA, USA). The species differs from its congeners mainly by the shape of the female carapace and by the morphology of the hemipenis, especially of the distal lobe and the copulatory process. The literature on the genus is reviewed and the synonymy of the fossil Cytheridella boldii Purper, 1974 with the type species C. ilosvayi Daday, 1905, both described from South America, is confirmed. The status of Cytheridella americana (Furtos, 1936) is reverted to that of \"uncertain species\". Beside the type species and the new species, the genus currently includes only three further species from Africa: C. monodi Klie, 1936, C. damasi Klie, 1944 (with synonym C. chariessa Rome, 1977), and C. tepida Victor, 1987. The morphology of the new species is discussed in comparison with the congeneric species, especially regarding the valve ornamentation, the structure and function of the third thoracopod, the hemipenis and the caudal ramus. It is suggested that C. whitmani is a recent invasive species in the lakes of the Cape Cod peninsula. Its occurrence at northern latitudes is unexpected, as its congeneric species are consistently (sub-) tropical.
Journal Article
Ecology of freshwater ostracods from Northern Patagonia and their potential application in paleo-environmental reconstructions
In order to generate a database of the auto-ecology and distribution of Argentinian North Patagonian ostracods (Argentina), a survey in 40 aquatic systems has been carried out. For this purpose, we report the ostracod diversity and assess the relationships between ostracod occurrence and abundance considering abiotic environmental variables. Twenty-two ostracod species have been found, three of which first record for Neotropical region and one for Argentina. Conductivity, temperature, and energy level have significantly explained ostracod distribution and abundance. Based on host waters features, three ostracod assemblages have been recognized: (1) temperate waters with moderate to high conductivity have presented in Sarscypridopsis aculeata, Potamocypris unicaudata, Heterocypris hyalinus, and Cypridopsis vidua as typical fauna; (2) environments with flowing waters were dominated by Ilyocypris ramirezi and Heterocypris incongruens, whereas (3) in cold and low conductivity environments, Tonnacypris lutaria, Eucypris virens, and Bradleystrandesia fuscata were the characteristic taxa. Our data indicate that Patagonian ostracods are largely influenced by host waters features, mainly conductivity and temperature. Likewise, due to the fact that eight of the twenty-two identified taxa in this survey were recovered in Holocene sequences from Patagonia, this study provides valuable information for future paleo-environmental reconstructions in North Patagonia.
Journal Article
On Cytheridellawhitmani sp. nov. (Crustacea, Ostracoda) from Cape Cod (Massachusetts, USA), with a reappraisal of the taxonomy of the genus
Martens,
is described from lakes on Cape Cod (MA, USA). The species differs from its congeners mainly by the shape of the female carapace and by the morphology of the hemipenis, especially of the distal lobe and the copulatory process. The literature on the genus is reviewed and the synonymy of the fossil
Purper, 1974 with the type species
Daday, 1905, both described from South America, is confirmed. The status of
(Furtos, 1936) is reverted to that of \"uncertain species\". Beside the type species and the new species, the genus currently includes only three further species from Africa:
Klie, 1936,
Klie, 1944 (with synonym
Rome, 1977), and
Victor, 1987. The morphology of the new species is discussed in comparison with the congeneric species, especially regarding the valve ornamentation, the structure and function of the third thoracopod, the hemipenis and the caudal ramus. It is suggested that
is a recent invasive species in the lakes of the Cape Cod peninsula. Its occurrence at northern latitudes is unexpected, as its congeneric species are consistently (sub-) tropical.
Journal Article
Bivalved arthropods from the Middle Ordovician Winneshiek Lagerstaette, Iowa, USA
The Middle Ordovician (Darriwilian) Winneshiek Lagerstaette of northeast Iowa is preserved in a meteorite crater. Besides conodonts, the fossils are dominated by arthropods, particularly eurypterids and phyllocarids. Here we describe the bivalved forms, which include at least seven different taxa. The small phyllocarid Ceratiocaris winneshiekensis, new species, is the most abundant; it is the oldest representative of the Ceratiocarididae. A single incomplete abdomen and telson bearing furcal rami is reminiscent of notostracan branchiopods but its affinities are unknown. Decoracaris hildebrandi, new genus and species, is a rare form with a shield that extends anteriorly into a swollen horn and reaches lengths of 9 cm: it may represent a thylacocephalan crustacean but this cannot be confirmed without soft parts. Iosuperstes collisionis, new genus and species, is represented by suboval valves 10-25 mm long: its affinities are unknown. A probable leperditicopid, which ranges in length from 8 to 18 mm, is commonly preserved in a 'butterflied' configuration. It does not preserve the scars and sinuses characteristic of three-dimensionally preserved leperditicopids from elsewhere. Finally the fauna includes at least three ostracods, including a palaeocope with a granular surface and relief similar to Lomatopisthia, and a smooth ?podocope. The Winneshiek fauna differs from those of other Ordovician Lagerstaetten from restricted settings such as Airport Cove and William Lake in Manitoba (Katian) where, apart from ostracods, bivalved arthropods are absent, and Silurian examples such as Brandon Bridge (Telychian), which lacks eurypterids, and the Williamsville Member of the Bertie Formation (Pridoli) where conodont assemblages are absent.
Journal Article