Final Whorl Research Articles

The Influence of Geochemical Variation Among Globigerinoides ruber Individuals on Paleoceanographic Reconstructions

AbstractVariation among individuals within species is a biological precondition for co‐existence. Traditional geochemical analysis based on bulk averages facilitates rapid data gathering but necessarily means the loss of large amounts of potentially crucial information into variability within a given sample. As the sensitivity of geochemical analysis improves, it is now feasible to build sufficiently powerful datasets to investigate paleoclimatic variation at the level of individual specimens. Here, we investigate geochemical and morphological variation among the sensu stricto, sensu lato and sensu lato extreme subspecies of the workhorse extant planktic foraminifera Globigerinoides ruber. Our experimental design distinguishes between subspecies and intraspecific variability as well as the repeatability of laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS). We show that geochemical variability in Mg/Ca ratios is driven by differences in subspecies depth habitat and that ontogenetic trends in Mg/Ca ratios are evident in the final whorl, with the final chamber consistently showing depleted Mg/Ca. These ontogenetic trends are not driven by individual chamber or test size. The Mg/Ca value variance among individuals is ∼100 times higher than the variance among repeated laser spot analyses of single chambers, directing laboratory protocols towards the need to sample ecologically and environmentally homogeneous samples. Our results emphasize that we can use LA‐ICP‐MS to quantify how individual variability aggregates to bulk results, and highlights that, with sufficient sample sizes, it is possible to reveal how intraspecific variability alters geochemical inference.

Horizontal Distribution and Carbon Biomass of Planktonic Foraminifera in the Eastern Indian Ocean

Distribution and carbon biomass of planktonic foraminifera were investigated from the euphotic zone of the Eastern Indian Ocean during a two-month cruise, ‘Shiyan I’ (10 April–13 May 2014). Foraminifera species were collected through plankton net sampling at 44 locations (80.00°–96.10° E, 10.08° N–6.00° S). The temperature (°C) ranged between 12.82 and 31.8 °C, the salinity ranged between 32.5 and 35.5, and chlorophyll-a concentrations ranged between 0.005 µg/L and 0.89 µg/L. A total of 20 taxa were identified based on the spherical chamber shell, spines, and a final whorl which were examined under light microscopy and scanning electron microscopy. Dominant species that were characterized by the high dominant index Y > 0.14–0.46 were Globigerina bulloides, Globigerinoides ruber white, Globigerinella siphonifera, Turborotalita quinqueloba, and Globigerinella calida, contributing to the community up to 86%. The shell size of collected taxa was from 51 to 508 μm and the total carbon biomass was estimated to be between 0.062 µg C m–3 and 26.52 µg C m–3. The high carbon biomass was recorded at two stations in the equator zone. Due to its large size, Globorotalia menardii had total carbon biomass of 3.9 µg C m–3, followed by G. calida 0.68 µg C m−3, Trilobatus sacculifer 0.38 µg C m–3, Orbulina universa 0.56 µg C m–3, and G. ruber white 0.22 µg C m–3, respectively. The Pearson correlation analysis showed that the temperature and chlorophyll-a were two explanatory environmental variables that were found to be highly significant (p < 0.05) and that triggered the distribution and abundance of dominant foraminifera species in the study region. Overall, high abundances and carbon biomass were derived from the euphotic zone and equatorial region of the Eastern Indian Ocean.

Uvigerina agglutinata n.sp. a new Holocene benthic foraminifer with an outer agglutinated layer from the central Red Sea

This paper describes a new deep-sea foraminifer which has possibly evolved a way to use sediment particles from its surroundings to increase its density. The benthic foraminifer recovered from Red Sea planktonic ooze shares some similarities with two well-established Uvigerina species Uvigerina auberiana d'Orbigny, 1826 and the extinct Uvigerina auberiana var. attenuata Cushman & Renz, 1941. However, it differs from the two species mainly by the incorporation of sediment grains into its external wall. Uvigerina agglutinata n.sp. is characterized by its initially triserial coiling, which changes to biserial in the middle part and eventually becomes uniserial in final whorl. The most diagnostic feature of this species is the incorporation of different shapes and sizes of detrital calcium carbonate grains into its outer wall.

Taxonomy and phylogeny of Albian-Maastrichtian planispiral planktonic foraminifera traditionally assigned to Globigerinelloides

We propose a considerably revised taxonomy and phylogeny for Albian-Maastrichtian planispiral planktonic foraminiferal species that have traditionally been included in Globigerinelloides. The revised taxonomy is necessary because of a ~6 m.y. gap between the extinction of planispiral species during the late Aptian and the next younger occurrence of planispiral species in the middle Albian. Our stratophenetic taxonomic groupings utilize ontogenetic morphometric data, shell wall ultrastructure, and general morphologic features observed from Scanning Electron Microscope and X-radiograph images of primary type specimens and globally distributed hypotype specimens. The planispiral lineage Laeviella n. gen., whose type species is La. bentonensis (Morrow), first appeared in the middle Albian and is postulated to have evolved from the evolutionary series Ticinella primula Luterbacher-Laviella primuloides n. sp. Laeviella is characterized as having a smooth to finely pustulose wall texture and a moderate chamber size increase rate. Two additional species, La. tururensis (Bronnimann) and La. bollii (Pessagno), are included in Laeviella with the youngest species of the genus, La. bollii, becoming extinct during the late Campanian. Planohedbergella, with Plh. aspera (Ehrenberg) as its type species, is revised to include 10 species that show a wide variation in chamber arrangement, wall microstructure and test morphology, but all have a moderately to coarsely pustulose wall texture on some or most final whorl chambers. Its stratigraphic range is from the late Albian-Cretaceous/Paleogene boundary. The oldest species is Plh. ultramicra (Subbotina), which evolved from Planomalina pulchella Todd and Low during the late Albian. Planohedbergella circularis n. sp. is described as a new late Campanian-Maastrichtian species representing forms with evolute coiling, a large number of final whorl chambers, and a slow chamber size increase rate. Polycamerella n. gen. is described as a monospecific genus, with Po. tardata n. sp. as the type species. It is a small, biapertural form with a very slow chamber expansion rate and a stratigraphic range from the late Campanian-Maastrichtian. The ancestor of Po. tardata, is tentatively identified as Plh. ultramicra.

Oligocene Planktic Foraminiferal Taxonomy and Evolution: An Illustrated Revision of Ocean Drilling Program Site 803

ABSTRACT The Oligocene (33.9–23.0 Ma) has historically proven to be a difficult interval to examine with respect to planktic foraminifera; the tendency for many of the taxa to be basically globigerine in shape, with 4 or 5 chambers in the final whorl means differences between species are limited. Recently, an international working group has attempted to clarify the Oligocene planktic foraminiferal taxonomy, with the goal of establishing phylogenetically-consistent generic and species concepts. A relatively expanded and continuous Oligocene section recovered at Ocean Drilling Program Site 803 in the western equatorial Pacific was previously studied by Leckie et al. (1993) using fairly conservative species concepts. Since 1993, foraminiferal biostratigraphic datum age calibrations have changed, and so revised sedimentation rates for the 220-m thick Oligocene sequence are actually more constant than previously thought. As a part of the recent taxonomic revision, this site was reevaluated and numerous additional taxa are recorded at this location. Macroevolutionary rates are calculated from the occurrences, and increased extinction is found within the late Oligocene, counter to the expectations laid out in broader-scale macroevolutionary studies. An effort is made here to describe the diagnostic features, which can be used to distinguish all taxa under a standard binocular microscope. Finally, several figures of scanning electron microscope photomicrographs (from Site 803 and tropical Atlantic Ocean ODP Site 628) depict features used to describe and differentiate important, but difficult or homeomorphic taxa, with the hope that these figures can be used by other workers at the microscope attempting to do Oligocene taxonomy-based studies.

Srinivasania Sundarbanensisgen. et sp. nov., a New Agglutinated Benthic Foraminifer from the World's Largest Mangrove Ecoregion, the Sundarbans, India

ABSTRACTWe describe Srinivasania sundarbanensis n. gen. et sp. nov., a multichambered textulariid foraminifer from the world's largest mangrove ecosystem, the Sundarbans, India. The new genus has an agglutinated wall structure, planispirally coiled test, and a single high-arched equatorial aperture located at the base of the final chamber with a narrow, agglutinated lip and with morphological similarity to the genera GobbettiaDhillon, 1968, and HaplophragmoidesCushman, 1910. Phylogenetic analyses, using partial small subunit rRNA gene, partial large subunit rRNA gene, and concatenated (LSU+SSU) sequence data clearly show the placement of this new taxon among other textulariid foraminifers, distant from all other genera in a strongly supported clade. In the new genus and species, the test is discoidal, measuring 100 to 350 µm in diameter with six to seven chambers in the final whorl. Elemental characterization (SEM-EDS) of the agglutinated test wall reveals a preference for quartz grains (SiO2) to construct its test. It is a common species and is presently known only from the northern marsh environments of Indian Sundarbans.

Vertical distribution of planktic foraminifera through an oxygen minimum zone: how assemblages and test morphology reflect oxygen concentrations

Abstract. Oxygen-depleted regions of the global ocean are rapidly expanding, with important implications for global biogeochemical cycles. However, our ability to make projections about the future of oxygen in the ocean is limited by a lack of empirical data with which to test and constrain the behavior of global climatic and oceanographic models. We use depth-stratified plankton tows to demonstrate that some species of planktic foraminifera are adapted to life in the heart of the pelagic oxygen minimum zone (OMZ). In particular, we identify two species, Globorotaloides hexagonus and Hastigerina parapelagica, living within the eastern tropical North Pacific OMZ. The tests of the former are preserved in marine sediments and could be used to trace the extent and intensity of low-oxygen pelagic habitats in the fossil record. Additional morphometric analyses of G. hexagonus show that tests found in the lowest oxygen environments are larger, more porous, less dense, and have more chambers in the final whorl. The association of this species with the OMZ and the apparent plasticity of its test in response to ambient oxygenation invites the use of G. hexagonus tests in sediment cores as potential proxies for both the presence and intensity of overlying OMZs.

Alicantina, A New Eocene Planktonic Foraminiferal Genus For the Lozanoi Group

Abstract The lozanoi group appeared in the early Eocene and includes two taxa, Globigerina prolata Bolli, 1957, characterized by a globigerinid test, and Globigerina lozanoi Colom, 1954, which is distinguished by having 5–6 globular chambers in the final whorl that tend to increase the height of the coiling axis to a medium-high trochospire and an intraumbilical aperture that tends to extend extraumbilically. The two species both possess a non-spinose, irregularly cancellate wall texture (dutertrei-type) very similar to the praemuricate-type typical of the Paleocene genus Praemurica Olsson et al., 1992. However, the stratigraphic gap and the lack of intermediate morphotypes between the two groups suggest that the lozanoi group evolved independently from a different ancestor. Therefore, Alicantina n. gen. is here proposed to accommodate the species lozanoi and prolata, the ancestor of which is presently unknown.

Haplophragmoides arcticus, n. sp. - a new species from the Pleistocene of the Central Arctic Ocean

A new agglutinated benthic foraminifer, Haplophragmoides arcticus, n.sp., is described from the Middle Pleistocene of Core 87/030-1 collected from the Lomonosov Ridge, Central ArcticOcean. The species is characterized by its deep umbilicus, and circular outline that becomes lobate in the youngest part of the test. The adult specimens have eight triangular chambers in the final whorl. The species is found in an assemblage consisting entirely of agglutinated foraminifera. The species shows closest affinity to some Paleogene species described from flysch-type assemblages, and may have regional stratigraphic importance for the Arctic Pleistocene.

Evolutionary prospection in the Neogene planktic foraminifer Globorotalia menardii and related forms from ODP Hole 925B (Ceara Rise, western tropical Atlantic): evidence for gradual evolution superimposed by long distance dispersal?

Evolutionary prospection is the study of morphological evolution and speciation in calcareous plankton from selected time-slices and key sites in the world oceans. In this context, the Neogene menardiform globorotalids serve as study objects for morphological speciation in planktic foraminifera. A downcore investigation of test morphology of the lineage of G. menardii-limbata-multicamerata during the past 8 million years was carried out in the western tropical Atlantic ODP Hole 925B. A total of 4669 specimens were measured and analyzed from 38 stratigraphic levels and compared to previous studies from DSDP Sites 502 and 503. Collection of digital images and morphometric measurements from digitized outlines were achieved using a microfossil orientation and imaging robot called AMOR and software, which was especially developed for this purpose. Most attention was given to the evolution of spiral height versus axial length of tests in keel view, but other parameters were investigated as well. The variability of morphological parameters in G. menardii, G. limbata, and G. multicamerata through time are visualized by volume density diagrams. At Hole 925B results show gradual test size increase in G. menardii until about 3.2 Ma. The combination of taxonomic determination in the light microscope with morphometric investigations shows strong morphological overlap and evolutionary continuity from ancestral to extant G. menardii (4–6 chambers in the final whorl) to the descendent but extinct G. limbata (seven chambers in the final whorl) and to G. multicamerata (≥8 chambers in the final whorl). In the morphospace defined by spiral height (δX) and axial length (δY) Globorotalia limbata and G. multicamerata strongly overlap with G. menardii. Distinction of G. limbata from G. menardii is only possible by slight differences in the number of chambers of the final whorl, nuances in spiral convexity, upper keel angles, radii of osculating circles, or by differences in reflectance of their tests. Globorotalia multicamerata can be distinguished from the other two forms by more than eight chambers in the final whorl. It appeared as two stratigraphically separate clusters during the Pliocene. Between 2.88 and 2.3 Ma G. menardii was severely restricted in size and abundance. Thereafter, it showed a rapid and prominent expansion of the upper test size extremes between 2.3 and 1.95 Ma persisting until present. The size-frequency distributions at Hole 925B are surprisingly similar to trends of menardiform globorotalids from Caribbean DSDP Site 502. There, the observations were explained as an adaptation to changes in the upper water column due to the emergence of the Isthmus of Panama. In light of more recent paleontological and geological investigations about the completion of the permanent land connection between North and South America since about 3 Ma the present study gives reason to suspect the sudden test size increase of G. menardii to reflect immigration of extra-large G. menardii from the Indian Ocean or the Pacific. It is hypothesized that during the Late Pliocene dispersal of large G. menardii into the southern to tropical Atlantic occurred during an intermittent episode of intense Agulhas Current leakage around the Cape of Good Hope and from there via warm eddy transport to the tropical Atlantic (Agulhas dispersal hypothesis).

TAXONOMIC REEXAMINATION AND TYPE-LOCALITY ASSEMBLAGE CHARACTERIZATION OF THE LATE ALBIAN PLANKTONIC FORAMINIFERA HEDBERGELLA YEZOANA TAKAYANAGI AND IWAMOTO, 1962, FROM JAPAN

Research Article| October 01, 2012 TAXONOMIC REEXAMINATION AND TYPE-LOCALITY ASSEMBLAGE CHARACTERIZATION OF THE LATE ALBIAN PLANKTONIC FORAMINIFERA HEDBERGELLA YEZOANA TAKAYANAGI AND IWAMOTO, 1962, FROM JAPAN Atsushi Ando Atsushi Ando * Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, MRC 121, Washington, D.C. 20013-7012 *Correspondence author: E-mail: AndoA@si.edu Search for other works by this author on: GSW Google Scholar Author and Article Information Atsushi Ando * Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, MRC 121, Washington, D.C. 20013-7012 *Correspondence author: E-mail: AndoA@si.edu Publisher: Cushman Foundation for Foraminiferal Research Received: 21 Jul 2011 Accepted: 30 Jun 2012 First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 © 2012 Cushman Foundation for Foraminiferal Research Journal of Foraminiferal Research (2012) 42 (4): 271–285. https://doi.org/10.2113/gsjfr.42.4.271 Article history Received: 21 Jul 2011 Accepted: 30 Jun 2012 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Atsushi Ando; TAXONOMIC REEXAMINATION AND TYPE-LOCALITY ASSEMBLAGE CHARACTERIZATION OF THE LATE ALBIAN PLANKTONIC FORAMINIFERA HEDBERGELLA YEZOANA TAKAYANAGI AND IWAMOTO, 1962, FROM JAPAN. Journal of Foraminiferal Research 2012;; 42 (4): 271–285. doi: https://doi.org/10.2113/gsjfr.42.4.271 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract The late Albian planktonic foraminifera Hedbergella trocoidea yezoanaTakayanagi and Iwamoto, 1962, from Japan, whose primary distinguishing feature is 7–8 chambers in the final whorl, has been internationally cited with a species rank as Hedbergella yezoana. Still, its taxonomic position is not well understood, as manifested by the fact that published hypotypes have six or fewer chambered forms, and such ambiguity is due partly to a lack of updated knowledge about the primary types (a holotype and single paratype), topotypes, and hypotypes from the northwestern Pacific region. This study reexamines the species concept of Hd. yezoana through uncoated SEM observations of the primary types and newly obtained type-locality material. The holotype is synonymous with Ticinella primula Luterbacher, 1963, as judged by its uneven wall surface, pseudoplanispiral (slightly streptospiral) mode of coiling, somewhat tangentially elongate last chambers, and a possible porticus-like structure. The topotypes exhibit important characters such as supplementary apertures and well-developed portici, thus confirming the synonymy of Hd. yezoana and T. primula. This outcome, however, is troublesome because T. primula is the widely used name for this morphology, and accepting the priority of “Ticinella yezoana” affects the nomenclatural stability in Cretaceous planktonic foraminifera. Conservation of the junior name T. primula is supported not only by the insufficient preservation of the Hokkaido material but also by the concept of Article 23.9 (reversal of precedence) in the International Code of Zoological Nomenclature (4th edition, 1999), although a ruling from the Zoological Commission would be eventually necessary. The paratype, in contrast, exhibits a smooth, microperforate wall, and is identified in open nomenclature as Microhedbergella sp. A (multi-chambered form). In addition to this wall-surface feature, this potential new Microhedbergella taxon differs from the “Hd. yezoana” holotype (and hence from T. primula) by lacking a streptospiral mode of coiling, exhibiting isomorphic globular chambers between the umbilical and spiral sides, and possessing a very poorly developed or nearly absent lip.The type-locality assemblage of “Hd. yezoana” is marked by the common occurrence of several other “ticinellid” taxa (Biticinella breggiensis and at least three species of Ticinella) and Microhedbergella with very rare Favusella. The Microhedbergella specimens have a remarkably wide range of morphologies, some comparable to those recorded in a local Texas assemblage, but the rest undescribed. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Morphological variability of the planktonic foraminifer Neogloboquadrina pachyderma from ACEX cores: Implications for Late Pleistocene circulation in the Arctic Ocean

Planktonic foraminifera populations were studied throughout the top 25 meters of the IODP ACEX 302 Hole 4C from the central Arctic Ocean at a resolution varying from 5cm (at the top of the record) to 10cm. Planktonic foraminifera occur in high absolute abundances only in the uppermost fifty centimetres and are dominated by the taxa Neogloboquadrina pachyderma. Except for a few intermittent layers below this level,most samples are barren of calcareous icrofossils. Within the topmost sediments, Neogloboquadrina pachyderma specimens present large morphological variability in the shape and number of chambers in the final whorl, chamber sphericity, size, and coiling direction. Five morphotypeswere identified among the sinistral (sin.) population (Nps-1 to Nps-5), including a small form (Nps-5) that is similar to a non-encrusted normal form also previously identified in the modern Arctic Ocean watermasses. Twenty five percent of the sinistral population is made up by large specimens (Nps-2, 3, 4), with a maximal mean diameter larger than 250µm. Following observations made in peri-Arctic seas (Hillaire–Marcel et al. 2004), we propose that occurrence of these large-sized specimens of N. pachyderma (sin.) in the central Arctic Ocean sediments could sign North Atlantic water sub-surface penetration.

PARATROCHAMMINA MINUTISSIMA N. SP. IN BRACKISH, MARINE-DERIVED LAKES OF THE VESTFOLD HILLS, EAST ANTARCTICA

Paratrochammina minutissima n. sp. is described from Abraxas and Ace Lakes in the Vestfold Hills, East Antarctica. The species is characterized by very small size (120 mm diameter), 4K chambers in the final whorl, weak adherence of particles to the tectin chamber lining and a relatively prominent proloculus. Similar species occur in the fully marine environment and often in the abyssal ocean. Subfossil tests were observed in sediment cores from Abraxas Lake and nearby Ace Lake. Apparently, living specimens also occurred in plankton samples from Abraxas Lake, possibly indicating a lifestyle partly attached to zooplankton or floating debris, or floating unattached on density surfaces within the meromictic lake. The distribution of subfossil Paratrochammina minutissima in the sediments of Ace Lake was consistent with a marine origin for the species, while the distribution in the Abraxas Lake sediment indicated that the lake might predate the last glacial maximum.

A NEW PLANKTONIC FORAMINIFER (FAMILY HEDBERGELLIDAE LOEBLICH AND TAPPAN, 1961) FROM THE LOWER CAMPANIAN SEDIMENTS OF THE FALKLAND PLATEAU, SOUTH ATLANTIC OCEAN (DSDP SITE 511)

Liuella falklandica nov. gen., nov. sp. is a planktonic foraminifer of the Late Cretaceous (lower Campanian) that is characterized by the following combination of features: imperforate peripheral band throughout the final whorl, smooth chamber surface and finely perforate to macroperforate test wall with crater-like perforations on the earlier chambers of the test. It is included in the Subfamily Hedbergellinae due to its strong resemblance in gross test architecture to Hedbergella planispira (Tappan) of the late Albian-Santonian, presumably its ancestor. The genus is monospecific.

TAXONOMIC RE-EVALUATION AND PHYLOGENY OF THE STELLATE PLANKTONIC FORAMINIFERAL GENUS HASTIGERINOIDES BRONNIMANN, 1952

The Late Cretaceous (Coniacian-Santonian) planktonic foraminiferal genus Hastigerinoides is emended. A new species, H. atlanticus nov. sp., is proposed for the tests with one or rarely two last-formed chambers that are strongly radially elongate and distally tapering in the final whorl. Hastigerinoides consists of three phylogenetically related species: H. clavata (Bronnimann, 1952), H. atlanticus nov. sp., and H. alexanderi (Cushman, 1931). This genus evolved from Globigerinelloides escheri , a Coniacian-middle Campanian, globular- to suglobular-chambered species.

Morphological variability of Globorotalia menardii (planktonic foraminifera) in two DSDP cores from the Caribbean Sea and the Eastern Equatorial Pacific

Variability in the test of Globorotalia menardii during the past 8 million years has been investigated at DSDP Site 502A (Caribbean Sea) and DSDP Site 503A (Eastern Equatorial Pacific). Measurements were made of spire height (∂x), maximum diameter (∂y), the tangent angles of the upper and lower peripheral keels (Φ1, Φ2, respectively), the number of chambers in the final whorl, and the area of the silhouette in keel view. Four morphotypes alpha, beta, gamma, and delta were distinguished. Morphotype alpha was found in strata ranging in age from the Late Miocene through the Holocene. It shows a continuous increase in ∂x and ∂y until the Late Pleistocene. During and after the final closure of the ancient Central American Seaway (between 2.4 Ma and 1.8 Ma) there was a rapid increase in the area of the test in keel view. At the Caribbean Sea site, morphotype beta evolved during the past 0.22 Ma. It is less inflated than alpha and has a more delicate test. In the morphospace of ∂x vs. ∂y, morphotypes alpha and beta can be distinguished by a separation line ∂y = 3.2 * ∂x - 160 (∂x and ∂y in µm). Plots of morphotype alpha are below that line, those of beta are above it. Morphotype alpha is taken to be Globorotalia menardii menardii Parker, Jones & Brady (1865) and includes G. menardii 'A' Bolli (1970). Morphotype beta is identified as G. menardii cultrata (d'Orbigny). Morphotypes gamma and delta are extinct Upper Miocene to Pliocene forms which evolved from morphotype alpha. They have a narrower Φ1 angle and more chambers (≥7) than morphotype alpha commonly with 5 to 6 chambers (7 in transitional forms). In contemporaneous samples morphotype delta can be distinguished from gamma by a smaller value of Φ1 and 8 or more chambers in the final whorl. Morphotype gamma is taken to be G. limbata (Fornasini, 1902) and includes the junior synonym G. menardii 'B' Bolli (1970). Morphotype delta is G. multicamerata Cushman & Jarvis (1930). With the exception of the Late Pleistocene development of G. menardii cultrataonly in the Caribbean the morphological changes of G. menardii at DSDP Sites 502A and 503A are similar. The development from the ancestral G. menardii menardii of the G. limbata - G. multicamerata lineage during the Pliocene and of G. menardii cultrata during the Late Pleistocene suggests responses at the two sites to a changing palaeoceanography during and after the formation of the Isthmus of Panama.

Comparison of CART and discriminant analysis of morphometric data in foraminiferal taxonomy

Paleontologists use statistical methods for prediction and classification of taxa. Over the years, the statistical analyses of morphometric data are carried out under the assumption of multivariate normality. In an earlier study, three closely resembling species of a biostratigraphically important genus Nummulites were discriminated by multi-group discrimination. Two discriminant functions that used diameter and thickness of the tests and height and length of chambers in the final whorl accounted for nearly 100% discrimination. In this paper Classification and Regression Tree (CART), a non-parametric method, is used for classification and prediction of the same data set. In all 111 iterations of CART methodology are performed by splitting the data set of 55 observations into training, validation and test data sets in varying proportions. In the validation data sets 40% of the iterations are correctly classified and only one case of misclassification in 49% of the iterations is noted. As regards test data sets, nearly 70% contain no misclassification cases whereas in about 25% test data sets only one case of misclassification is found. The results suggest that the method is highly successful in assigning an individual to a particular species. The key variables on the basis of which tree models are built are combinations of thickness of the test (T), height of the chambers in the final whorl (HL) and diameter of the test (D). Both discriminant analysis and CART thus appear to be comparable in discriminating the three species. However, CART reduces the number of requisite variables without increasing the misclassification error. The method is very useful for professional geologists for quick identification of species.

Revised taxonomy, <i>An Atlas of British Recent Foraminiferids</i>

Abstract. Since the publication of An Atlas of British Recent Foraminiferids (Murray, 1971) there have been many taxonomic changes. Some result from the revised generic classification summarized by Loeblich & Tappan (1987), some from later taxonomic revision, while others are corrections. In the following list, the name used in 1971 is followed by the revised name. Where the generic assignment is after Loeblich & Tappan (1987) the new name is listed without a reference. OD stands for original designation, i.e. the species is type of the genus. Brief explanations are given as appropriate.Pl. 1: Reophax scottii Chaster = Leptohalysis scottii (Chaster); thin, delicate and flexible test.Pl. 4: Cribrostomoides jeffreysii (Williamson) = Veleroninoides jeffreysii (Williamson); evolute planispiral test with interio-areal aperture (Jones et al., 1993)Pl. 8: Textularia sagittula Defrance group: as was noted on p. 31, this is a complex of variable forms. It includes Textularia bocki Höglund, Spirorutilis wrighti (Silvestri), and Textularia spp. 1–3 of Banner & Pereira (1981).Pl. 9: Textularia earlandi Parker = Morulaeplecta bulbosa Höglund; streptospiral initial end.Pl. 10: Trochammina globigeriniformis (Parker & Jones) var. pygmaea Höglund = Portatrochammina murrayi Brönnimann & Zaninetti, 1984; distinguished from T. g. var. pygmaea (apertural slit without a lip) by having a slit-shaped aperture ‘which extends below the border of the umbilical flap from the first chamber of the final whorl to the penultimate chamber’.Pl. 11: Trochammina ochracea (Williamson) = Lepidodeuterammina ochracea (Williamson); OD.Pl. 12: Trochammina rotaliformis Heron-Allen & Earland = Deuterammina sp.; according to Brönnimann . . .

Morphological Changes in Living Foraminifera and the Thermal Structure of the Water Column, Western North Atlantic

Changes in the morphological characteristics of living planktonic foraminiferal species, Globorotalia inflata and Globorotalia hirsuta, reflect the thermal structure of the upper water column in the western North Atlantic. Described using Fourier series analysis, morphologic variation in these species proves useful in extracting paleoceanographic information from fossil foraminiferal assemblages. For example, a well defined thermocline is accompanied by a significant decrease in elongation and quadrateness in G. inflata tests. Changes in the test shape of G. hirsuta are minimal in an area where the thermocline is poorly developed and water temperatures change gradually over a large water depth range (20over 800 meters). The observed shape changes in G. inflata with depth indicate that this globorotalid species adds an additional chamber in the final whorl with depth, dependent on the nature of the thermal stratification. This indication is corroborated by the fact that approximately 25% of the G. inflata specimens from below the thermocline have thin transparent fourth chambers in the final whorl compared to only 2% in waters above the thermocline. The results of this study further suggest that morphological changes observed in fossil populations of globorotalid species are to some degree the result of shape variation in the water column due to the nature of the thermal structure. The shape characteristics of fossil globorotalid foraminifera may possibly be used to determine the past hydrographic conditions of a region.

Everticyclammina minuta n. sp., foraminifère nouveau del'Hauterivien-Barrémien du Bassin de Paris

A new agglutinated foraminifer, Everticylammina minuta n. sp., from the Hauterivian-Barremian of the Paris Basin is described and illustrated (external morphology and internal structure). It is characterized by a small size, a compressed test with subparallel sides, a slight increase in volume, specially in width, from chamber to chamber, 9 to 14 chambers in the final whorl, and well developed, semicircular septal thicknesses beneath the aperture of each of the last chambers. The variability and the evolution of the species are pointed out. The nature of the associated faunas, together with the lithological characteristics of the succession, suggest that E. minuta n. sp. inhabited a quiet shallow marine environment (infralittoral zone), on muddy substrate, displaying some tolerance for slight changes in salinity.