bluuebunny/crossref_metadata_2025_split huggingface dataset:
A gradual morphological transition during a rapid speciation event in marginellid gastropods (Neogene; Dominican Republic)
Authors: Nehm Ross H. , Geary Dana H. 
Published: January 2018

Paleontological studies can bring to light two important aspects of the speciation process: long term patterns of morphological change, and the paleoenvironmental context of such changes. We examined the temporal patterns of morphological change and their geographic and paleoenvironmental context in species of Prunum (Marginellidae; Gastropoda) from the Neogene of the northern Dominican Republic. We document a speciation event from P. coniforme (Sowerby 1849) to P. christineladdae (Maury 1917) which is unusual in both its temporal expression, and in the relative clarity of the ecological setting for speciation.We believe that the changes in morphology from P. coniforme to P. christineladdae represent a speciation event. The two species are distinguished by several shell features, including overall shape, spire height, relative height of the top of the lip, and apertural denticulations. The nature and magnitude of these differences, compared with morphological differences among extant species of Prunum, indicate that separate species designations are warranted for P. coniforme and P. christineladdae. A sequence of stratigraphic and morphological intermediates between these species provides strong stratophenetic evidence for speciation.The stratigraphic interval characterized by intermediate morphologies includes approximately 22 m of section. Sedimentation rates yield estimates of approximately 73,000–275,000 years for our interval of morphologic change. This transitional interval represents between 0.6–2.5 % of the total duration of the ancestral species.The patterns of morphological change exhibited by the two species generally fit the predictions of punctuated equilibrium; change from ancestor to descendent is relatively rapid, outside the transitional interval species exhibit no directional morphologic trends, and the ancestral species persists after speciation.Our data reveal some information on the mode of speciation. Prunum species from our study area exhibit well-defined depth ranges. P. christineladdae occurs only in deep water deposits, whereas P. coniforme is common in shallow water deposits. Based on distributional data, we suggest that depth, or one or more of its associated variables, was critical to the isolation and evolution of P. christineladdae.
Shell matrix proteins - a potential tool for investigating the phylogenetic relationships of the Echinodermata
Authors: Polson Emma S. , Lawrence J. , Robbins L. L. 
Published: January 2018

The phylogenetic relationships of the echinoderms remains controversial due to the traditional use of morphological characters which do not reflect convergent evolution. While biochemical techniques and DNA analysis may be used in addition to morphological characters for analysis of living echinoderms, these tools cannot be extended to fossils. Shell matrix proteins - of echinoderms may be trapped and preserved for millions of years in fossil genera.Analysis of shell matrix protein from Astropectin irregularis, Luidia clathrata and Mellita tenuis, reveal the presence of at least three major proteins of approximate molecular weights 230, 83 and 17 kDa common to all species. Astropectin irregularis showed four additional major bands of molecular weights 150, 90, 52 and 35 kDa along with at least 12 minor bands. Luidia clathrata showed five additional major bands of molecular weights 99, 60, 40, 24 and 21 kDa and at least 13 other minor bands. Mellita tenuis showed three additional bands of molecular weights 115, 96, and 24 kDa along with at least 4 minor bands.As the three common proteins have been found in both seastars (A. irregularis and L. clathrata) and echinoids (Mellita tenuis), further analysis of these shell matrix proteins may be used to elucidate phylogenetic relationships within the Echinodermata. In addition homoplasies may be identified and phylogenetically reassessed.
The evolution of gastropod shell form: a developmental model illustrating the roles of heterochrony and non-heterochronic changes
Authors: Rice Sean H. 
Published: January 2018

The shape of an isometric gastropod shell can be described completely by specifying the pattern of shell secretion around the aperture (relative to aperture size) and the growth rate of the aperture itself. These descriptors provide a “natural” morphometric in that they correspond to the specific biological processes involved in constructing the shell.Describing shell form in this way allows us to specify what developmental changes must occur during the transition of one shell form to another. In particular, we can distinguish between transitions that can occur through purely heterochronic processes (changes in growth rate) and those that require a change in the specific pattern in which cells of the mantle lay down shell. We can also investigate just what changes occur during the ontogeny of non-isometric shells.Any change in either the pattern of shell secretion or the growth rate of the animal leads to changes in a number of classical morphometric measures, such as apex angle and whorl expansion rate. Those transformations resulting from changes in growth rate, however, are much more predictable than those resulting from changes in the pattern of shell production. A slight increase in the growth rate of the animal, for instance, produces a correspondingly slight increase in the apex angle and the rate of whorl expansion. By contrast, the consequences of a slight change in the pattern of shell production are highly sensitive to just how that change was achieved.Data from 8 genera of marine snails show that the variance within each genus, relative to the variance among all genera, is smaller for measures of aperture shape (which can only be altered through a change in the pattern of secretion of shell material) than for characters that can change through heterochronic transformations (such as apex angle). Furthermore, the shell forms of a number of non isometric shells can be described by a constant pattern of shell production and a variable growth rate.Heterochronic changes thus appear to be the preferred mechanism for changing phenotype in gastropod shells. Those characters that can only be altered by changing the pattern of shell production around the mantle, such as aperture shape, appear to be more conservative than those that can be changed through purely heterochronic transitions. This is consistent with the idea that mutations which alter many characters in a highly correlated manner have a higher probability of being favored by selection than those with relatively unpredictable consequences.
A possible archaeopriapulid trace fossil from the Middle Cambrian Stephen Formation, British Columbia
Authors: Rudkin David M. 
Published: January 2018

It is generally accepted that the extraordinary preservation of fossils in the Burgess Shale is at least partly due to the exclusion of large metazoan scavengers through rapid burial in an inimical environment. Disruption of individual organisms appears to have been largely the result of mechanical processes and/or microbial decay. The absence of bioturbation through much of the classic section, including Walcott's Phyllopod Bed, supports these arguments. However, macroscopic traces are known from other horizons within the Burgess Shale section and from lateral equivalents in the Stephen Formation a short distance south of the main locality.The sparse ichnoassemblage includes bedding-plane exposures of portions of compacted, parallel-sided burrows containing skeletal debris comprising fragmented and disarticulated hyoliths, small trilobites, and bracniopods. Walcott originally figured one such trace as Planolites sp. ? and noted, but offered no evidence for, an association with the archaeopriapulid Ottoia prolifica. This notion was subsequently rejected by Conway Morris.A recently collected specimen, from talus south of the main locality, contains a poorly preserved but recognizable body fossil of Ottoia within the outline of a “Planolites”. Although this juxtaposition may be accidental, a number of features of the association, and a consideration of the burrowing behaviour of modern priapulids, suggest that Ottoia could have been the generator of “Planolites”-like traces.
Investigation of the terrestrial occurrence and biological source of the petroleum geochemical biomarker oleanane
Authors: Taylor David W. , Moldowan J. Michael , Hickey Leo J. 
Published: January 2018

Oleanane is a triterpane that is commonly found in Late Cretaceous (Campanian) through Cenozoic marine and deltaic rocks and related oils. Based on its affinity to the β-Amyrin group of natural products and its abundance in Tertiary deltaic sediments and oils, such as in the Niger Delta, oleanane is thought to be a geochemical fossil of terrestrial flowering plants. The β-Amyrin group forms the basis of many angiosperm triterpenoids and triterpenoid saponins. These compounds appear in moderately advanced flowering plant lineages and are often used as a defense against herbivores. This group of compounds has not been reported from any other seed plant group, including conifers.We examined a suite of middle to early Cretaceous terrestrial sediments and plant fossils for the presence of oleanane. The existence of oleanane was documented by Gas Chromatography - Mass Spectrometry (GC-MS) and confirmed with Metastable Reaction Monitoring (MRM) GC-MS.Oleanane was identified from fossil bennettitaleans, an extinct group of seed plants. Cycadeoidea paynei and C. superba are permineralized fossil stems and are from the Early Cretaceous Inyan Kara Group of the Black Hills, SD. Oleanane was also found in carbonaceous compressed leaf fossils of Dioonites from the Barremian - early Aptian (Zone I) of the Potomac Group from Richmond, VA. This increases the number of seed plant groups known to have oleanane, and is of additional interest as the bennettitaleans are thought to be closely related to angiosperms.Oleanane was not found in contemporaneous fossil conifers. Our sample consisted of fossil conifer wood collected from the Campanian Magothy Beds of Martha's Vineyard, MA; the Cenomanian Raritan Formation of Sayreville, NJ; and the Barremian - early Aptian Patuxent Formation of Greenbelt, MD.Confirmed reports of oleanane have been from Late Cretaceous and younger marine sediments. We now report oleanane from Early Cretaceous terrestrial strata of the Inyan Kara Group. In addition we systematically sampled the sequence of Cretaceous terrestrial sediments of the coastal plain of the eastern U.S.A, and found oleanane in the Barremian - early Aptian (Zone I) Potomac Group. Preliminary data indicate variation in the occurrence of oleanane in contemporaneous Early Cretaceous sites from the Potomac Group. The localities accumulated in different depositional environments and the occurrence may be controlled by lithofacies.
The coccolithophore Emiliania huxleyi and global climate
Authors: Westbroek Peter 
Published: January 2018

Cells of Emiliania huxleyi are surrounded by ‘coccoliths', minute, elegant scales of calcium carbonate. In all the oceans, particularly at mid-latitudes, this species forms gigantic blooms, readily visualized by satellite imagery. Coccolith-bearing organisms, of which E. huxleyi is by far the most abundant representative, are the major contributors to the ocean floor limestone sediments, and this in turn is the largest long-term sink of inorganic carbon on earth. In addition, E. huxleyi blooms emit vast amounts of dimethyl-sulphide (DMS), a gas which, on oxidation, is a dominant source of cloud nuclei. The profusion of E. huxleyi and its intimate involvement with the global biogeochemical cycles of both carbon and sulphur make it a key component of the greenhouse effect (CO2), natural acid rain and albedo regulation.E. huxleyi blooms are often almost monospecific. They can be visualized by satellite imagery and leave highly characteristic skeletal and macromolecular markers which accumulate on the deep-sea floor as a long-term record of their history. The organism is easily cultured in the laboratory and molecular genetical, biochemical and physiological studies are underway.We focus on Emiliania huxleyi as a model organism to study interactions between oceanic plankton and climate. Benefits of this approach are: (1) to highlight the idiosyncratic non-linear character of these interactions; (2) to reveal the intimate coupling of the oceanic carbon cycle and DMS productivity; and (3) to allow an integrated modelling and experimental approach, integrating multi-disciplinary studies that range from the global down to the macromolecular level and through geological time. E. huxleyi coccoliths and specific biomarkers preserved in the geological archive not only provide information on the distribution of this organism in the geological past. The connection with extensive neontological research offers a unique opportunity to reconstruct the development of the entire E. huxleyi system, including its multifarious climatic interactions, through geological time.The ‘Global Emiliania Modeling Initiative’ (GEM), started in 1990, is a European research program intended to investigate and model the Emiliania huxleyi system.
Declining importance of trilobites in Ordovician nearshore communities: displacement or dilution?
Authors: Westrop Stephen R. , Tremblay James V. , Landing Ed 
Published: January 2018

Declining importance of trilobites was a key feature of Ordovician community “evolution”. Previous work has shown that replacement of trilobite-dominated communities by mollusc- and brachiopod-dominated communities was diachronous, occurring initially in nearshore settings. The processes responsible for these changes remain unclear, although many previous discussions have invoked some form of displacement of dominants of one community by those of another.New data from more than thirty large collections made from nearshore facies at five localities in Canada and the northern United States indicate that, in this setting, trilobite species diversity maintained a constant low level (mean and mode of 3 species) between the Early Upper Cambrian (Marjuman) and the Late Middle Ordovician (Blackriveran). Reorganization of nearshore communites proceeded by addition of new elements, especially molluscs, from the Late Cambrian (Sunwaptan) onwards. Decline in the relative importance of trilobites was a case of dilution as species of new clades accumulated, rather than actual displacement. Trilobites appear to have been passive bystanders in Ordovician nearshore community “evolution”. Towards the end of the Ordovician, trilobites vacated nearshore environments in the Appalachian region. However, this appears to be related to environmental changes associated with progradation of clastic wedges during the development of the Taconic foreland basin.A process of dilution may at least partly explain the offshore retreat of trilobite-dominated assemblages during the Ordovician. Offshore trilobite assemblages reached much greater species diversity than those of nearshore settings, so that their dilution via the addition of species of newly radiating clades would have proceeded more slowly. That is, trilobite-dominated paleocommunities may have persisted into the Ordovician in the outer shelf simply because this was the region in which, historically, they attained maximum species richness. Moreover, given the existence of a general pattern of increasing total species diversity of communities from nearshore to offshore sites, the tendency for newly radiating clades to attain maximum species richness offshore is not surprising: they are merely conforming to a general, environmentally-related diversity gradient that has existed throughout the Phanerozoic.
Paleocene-Eocene floral and climatic change in the Bighorn Basin
Authors: Wing Scott L. , Hickey Leo J. 
Published: January 2018

Nearly autochthonous plant fossil assemblages are abundant in a variety of fluvial sub-environments in the Fort Union and Willwood Fms. of the Bighorn Basin (BHB), including abandoned channel fills, channel margins, levees, splays, and floodplain backswamps. Heterogeneity in the stratigraphic and geographic distribution of plant-bearing deposits limits our ability to resolve temporal change in floras and climate because depositional environment strongly affects floral composition, and must be considered in any analysis of floral change.Plant-bearing levee, splay, and backswamp strata are common through much of the Fort Union Fm. in both the central and northern BHB. In the central basin, such deposits are abundant in the lower 200 m and upper 150 m of the Willwood Fm. with a gap from 350 to 620 m. In the northern BHB, the Willwood Fm. is almost entirely devoid of such plant-bearing deposits. Abandoned channel fills are scattered throughout the Fort Union and Willwood Fms. with the exception of the upper Willwood in the northern BHB and the 460-620 m interval of the Willwood in the central BHB. Deposition of plant-bearing floodplain backswamps was probably controlled by rates of aggradation, and the proximity and stability of major channels, as well as by regional climatic change. The formation of plant-preserving ponds was probably controlled less by climate than by the rate of channel cut-off and the degree to which channels reworked previous floodplain deposits. At a larger scale than these local depositional settings are sub-regional scale environments, including coal swamps, lakes, and conglomerate fans, that have a stratigraphic distribution controlled largely by tectonic activity.Samples of fossil floras matched for depositional environment and sampling effort reveal several long-term patterns. One, the greatest number of species and fastest rate of turnover are seen in the alluvial ridge environments; backswamp samples have fewer species and slower rates of turnover. Two, floristic change during the Paleocene was relatively slow, and the Paleocene/Eocene (Clarkforkian/Wasatchian) boundary is marked by just a few extinctions and originations. The most pronounced turnover in the BHB sequence occurred between the early and late Wasatchian, probably as a result of climatic drying. Three, species number decreased from the early to mid-Paleocene, then increased steadily from 8 spp./sample in the late Clarkforkian to >12 spp./sample in the late Wasatchian.Physiognomic analysis of floras indicates a rise in mean annual temperature from about 10° C in the Tiffanian to about 13° in the Clarkforkian and more than 18° in the early late Wasatchian; this may have been a major factor in the increasing diversity of the flora. Recent correlations of Bighorn Basin sections to standard marine zonations show that this warming trend was synchronous with global warming indicated by the oxygen isotope record.
Biology and functional morphology of Cloudina, the earliest known metazoan with a mineralized skeleton
Authors: Yue Zhao , Bengtson Stefan , Grant Stephen W.F. 
Published: January 2018

The earliest known skeletal metazoan, Cloudina, was widespread in the late Neoproterozoic. We report here on phosphatized specimens of Cloudina sp. from dolomites of the Dengying Formation, 30 m below the first Cambrian skeletal fauna, in the Lijiagou section, Shaanxi Province, China. The specimens exhibit new details of shell morphology and fine structure that offer insights concerning the mechanism of shell accretion and the selective pressures influencing skeletogenesis in metazaons.Cloudina formed curved to sinous tubular shells 0.2-8 mm in diameter and up to 4 cm in length. They consist of numerous thin (5-10 μm) calcareous layers, each in the form of a slightly flaring tube. New layers were deposited above and to one side of the previous layer, giving rise to a series of eccentrically nested shell laminae. Some of the phosphatized layers exhibit tight folding or wrinkling that may have been primary (imparting additional strength) or secondary (related to plastic deformation of organic-rich shell material). Pore space existed between terminal thin flanges, but concentric ridges may have served to strengthen the free standing portions of shell layers. SEM and cathodoluminescence of polished thin sections also reveal that each shell layer may itself have been constructed of an organized layering of organic matrix and carbonate, suggesting a fairly sophisticated biologic control over shell formation. The presence of circular holes, the size of which correlates positively with tube diameter, moreover, strongly suggests that one function of the shell was to protect the Cloudina organism from predatorial and/or parasitic attack.The taxonomic status of Cloudina remains problematic. Rare specimens of the Lijiagou Cloudina which show two younger tubes growing within an older single tube suggest that the organism was capable of asexual reproduction by longitudinal fission. Such a latent tendency is not compatible with previously proposed affinities with polychaete worms.
Remarkably High Hole Mobility Metal-Oxide Thin-Film Transistors
Authors: Shih Cheng Wei , Chin Albert , Lu Chun Fu , Su Wei Fang 
Published: January 2018

AbstractHigh performance p-type thin-film transistor (p-TFT) was realized by a simple process of reactive sputtering from a tin (Sn) target under oxygen ambient, where remarkably high field-effect mobility (μ
FE
) of 7.6 cm2/Vs, 140 mV/dec subthreshold slope, and 3 × 104 on-current/off-current were measured. In sharp contrast, the SnO formed by direct sputtering from a SnO target showed much degraded μ
FE
, because of the limited low process temperature of SnO and sputtering damage. From the first principle quantum-mechanical calculation, the high hole μ
FE
of SnO p-TFT is due to its considerably unique merit of the small effective mass and single hole band without the heavy hole band. The high performance p-TFTs are the enabling technology for future ultra-low-power complementary-logic circuits on display and three-dimensional brain-mimicking integrated circuits.
The MICALs are a Family of F-actin Dismantling Oxidoreductases Conserved from Drosophila to Humans
Authors: Wu Heng , Yesilyurt Hunkar Gizem , Yoon Jimok , Terman Jonathan R. 
Published: January 2018

AbstractCellular form and function – and thus normal development and physiology – are specified via proteins that control the organization and dynamic properties of the actin cytoskeleton. Using the Drosophila model, we have recently identified an unusual actin regulatory enzyme, Mical, which is directly activated by F-actin to selectively post-translationally oxidize and destabilize filaments – regulating numerous cellular behaviors. Mical proteins are also present in mammals, but their actin regulatory properties, including comparisons among different family members, remain poorly defined. We now find that each human MICAL family member, MICAL-1, MICAL-2, and MICAL-3, directly induces F-actin dismantling and controls F-actin-mediated cellular remodeling. Specifically, each human MICAL selectively associates with F-actin, which directly induces MICALs catalytic activity. We also find that each human MICAL uses an NADPH-dependent Redox activity to post-translationally oxidize actin’s methionine (M) M44/M47 residues, directly dismantling filaments and limiting new polymerization. Genetic experiments also demonstrate that each human MICAL drives F-actin disassemblyin vivo, reshaping cells and their membranous extensions. Our results go on to reveal that MsrB/SelR reductase enzymes counteract each MICAL’s effect on F-actinin vitroandin vivo. Collectively, our results therefore define the MICALs as an important phylogenetically-conserved family of catalytically-acting F-actin disassembly factors.