bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relationship between diatoms in surface sediments of the Atlantic Ocean and the biological and physical oceanography of overlying waters
Authors: Maynard Nancy G. 
Published: July 2016

The number of diatom valves and fragments per gram of surface sediment in the Atlantic Ocean accurately reflects diatom abundance in the overlying waters, without any evidence of significant lateral drift during settling to the sea bottom. The distribution pattern of the number of resting spores per gram is similar to that for the whole and fragmented diatom valves. Fresh water diatoms and opal phytoliths are abundant in the sediments off the west coast of Africa where they have been deposited by the Trade Winds.Despite the relatively small number of core tops analyzed, the abundance and distribution patterns of diatoms in the sediments exhibit striking similarities to the patterns of primary productivity, phosphates, and annual production of silica in suspension in surface waters. Areas with high phosphate values and primary productivity and, therefore, areas of upwelling can be inferred from the quantitative distribution of diatoms in the sediments. Q-mode factor analysis, based on the abundance of forty-two species in thirty-seven core tops, produced six diatom species assemblages whose distributions provide additional information on the positions of certain water masses and major currents.Since the data on the quantitative distribution of diatom valves as well as on the diatom assemblages in the sediments of the Atlantic Ocean today allow prediction of certain water mass characteristics and circulation patterns of the overlying waters, they therefore, permit the reconstruction of paleoceanographic circulation patterns in ancient Atlantic Oceans, using the diatom distribution in sediments from dated horizons.
Neutral Hypotheses and Patterns of Species Diversity: Fact or Artifact?
Authors: Thomas William R. , Foin Theodore C. 
Published: July 2016

Species diversity is a product of both biological interactions and physical-geographic factors. A model which eliminates biological interactions as a determinant of diversity can be used to assess the potential impact of physical and geographic factors operating alone on temporal trends in diversity (succession) and on spatial differences along latitudinal or environmental gradients. If a biologically neutral model can generate diversity patterns similar to those we observe, it can be argued that traditional hypotheses which depend on biological interactions are not the most parsimonious explanations for diversity patterns. If the neutral model approach supports a spectrum of possible hypotheses, perhaps the entire concept of species diversity can be discarded as a useful measure of community structure.An earlier analysis of this type supported the notion that diversity patterns can be adequately explained by physical disturbance, global geography gradients, and stochastic immigration and extinction events. Our neutral model analysis does not affirm this view. We argue that the coarse level at which simple colonization models operate does not permit strong conclusions regarding the underlying mechanisms. Detailed community analyses may provide the best evidence for the nature of structuring processes. Based on the evidence available in the literature, species diversity is likely to be generated by a small number of biological processes interacting with physical-geographic gradients.
Planar branch systems in colonial suspension feeders
Authors: McKinney Frank K. 
Published: July 2016

Among the various forms developed by marine colonial filter feeders, erect colonial fans have evolved in representatives of several phyla. Branches are relatively narrow, evenly spaced from one another, proliferate by bifurcation, and in most colonies continue from their point of origin to the distal margin of the colony. Their narrowness and uniform placement is apparently related to filling an area with multiple tentacle bells of similar size. The major architectural problem for such a colonial suspension feeder seems to be construction of a sheet composed of narrow branches such that water may be filtered as it flows through the sheet, between branches.The simplest form of the filtration sheets is a uniformly expanding wedge, in which new branches originate at regular intervals from the point of origin of the wedge. Variation in rate of addition of new branches results in more complex forms, such as paraboloids, flaring fans, spirals, and highly folded sheets.
Population structure of a pioneer and a later stage species in an Ordovician ecological succession
Authors: Walker Kenneth R. , Parker William C. 
Published: July 2016

Marine shelf lagoon deposits of Middle Ordovician age in Tennessee contain the record of repeated ecological successions which began on soft, azoic, terrigenous muds and progressed to a complex bryozoan-brachiopod community. The stages of succession formed a skeletal limestone bed. The process led to an interbedded shale-limestone stratigraphic sequence. The pioneer was the brachiopod Strophomena basilica which paved the soft mud with accumulated shells. Encrusting bryozoans colonized this shell pavement and were followed by ramose bryozoans. The final stages of succession included bryozoans, gastropods, pelecypods, and pelmatozoans but were dominated by the brachiopod Rostricellula rostrata.Measurements of total length, width, length to growth lines (Strophomena only), and thickness (Rostricellula only) were used to generate growth-rate, and survivorship curves for these two species. Strophomena shows low juvenile mortality, a moderate, linear growth-rate, and increased mortality in later ages. Rostricellula shows relatively higher juvenile mortality, a rapid non-linear growth rate, and nearly constant mortality. These attributes are contrary to expectations derived from theory, but can be understood in the light of autecological factors for each species. Adaptation to soft substrata was the primary factor controlling population dynamics in Strophomena, and crowding was the main factor in Rostricellula.
Species diversity in the Phanerozoic: a tabulation
Authors: Raup David M. 
Published: July 2016

On the basis of about 70,000 species citations in the Zoological Record, it is estimated that about 190,000 fossil invertebrate species were described and named through 1970. The true figure may be higher because of incompleteness of the Zoological Record or lower because the estimate does not account for synonymy.About 70% of the species were described from USSR, Europe, and North America. About 42% are Paleozoic, 28% Mesozoic, and 30% Cenozoic. In the Cambrian part of the sample, 75% of the species are trilobites. In the Mesozoic and Cenozoic, about 70% are either molluscs or protozoans.When the data are normalized for absolute time, diversity (species per million years) shows a Paleozoic high in the Devonian which is approximately four-tenths of the Cenozoic level.
The poor fossil record of the regular echinoid
Authors: Kier Porter M. 
Published: July 2016

The fossil record of echinoids is poor because soon after death they break apart into isolated plates. In the present seas regular echinoid species outnumber irregular species; whereas, in the Tertiary only 20% of the known echinoid species are regular. This suggests that regular echinoids are less likely to be preserved than irregular echinoids. The tests of regular echinoids are exposed to scavengers and currents upon their death, but irregular echinoids generally live buried in the sediment and are protected from these destructive forces. Furthermore, the tests of the regular echinoids lack the calcareous supports found in some irregular echinoids. The gut is not filled with sediment and its apical system is generally larger and more fragile. Finally, many regular echinoids live in environments less likely to be preserved in the sedimentary record.Although the irregular echinoid is more likely to be fossilized, its record is poor during some periods in the past. Although 1,014 irregular echinoid species are known from the Eocene, only 83 species are known from the Paleocene and only 343 are known from the Oligocene. Is this reduction because fewer species lived then or because they have not been preserved?
1. Theory, laboratory behavior, and field orientations
Authors: LaBarbera Michael 
Published: July 2016

(1) Hydrodynamic principles and experiments with empty shells predict that pressure distributions around brachiopod shells generated by ambient currents should, depending on the orientation of the shell relative to the current, either augment or oppose the ciliary-driven flow of water through the lophophore. For living articulate brachiopods with plectolophes or spirolophes, orientations where the anterior-posterior axis of the shell is parallel to the current direction should result in pressure distributions which oppose active pumping. This effect should be strongest when the excurrent region of the shell faces into the current. Orientations where the anterior-posterior axis is perpendicular to the current direction should result in pressure distributions which act in concert with active pumping, most strongly when one of the incurrent regions is directed into the current. These effects are independent of specific shell shape.(2) Laqueus californianus and Terebratulina unguicula actively reorient to currents in the laboratory, preferring orientations where the anterior-posterior axis of the shell is perpendicular to the current and the right-left axis is parallel to the current. Both species may traverse an arc as great as 120° to achieve their final orientation. Hemithyris psittacea also will actively reorient to currents, moving towards orientations where the anterior-posterior axis is perpendicular to the current. The maximum rotation observed for H. psittacea was 45°. Terebratalia transversa never reoriented in the laboratory.(3) Using epifaunal hydroid colonies as indicators of current direction, both Hemithyris psittacea and Terebratalia transversa are oriented in nature with the anterior-posterior axis of the shell perpendicular to the prevailing currents. While scuba diving, I confirmed this orientation phenomenon for T. transversa by direct measurement of the orientation of the brachiopods relative to prevailing currents.(4) Larval Terebratalia transversa avoid areas with current speeds greater than about 0.2 cm/s during metamorphosis and show no orientation to the ambient currents immediately after metamorphosis. Post-metamorphic T. transversa can actively reorient on the pedicle. The orientation observed in adults is probably achieved by active reorientation to local currents of post-zygolophe juveniles.(5) Threshold current speeds for reorientation in Laqueus californianus and Terebratulina unguicula are low and approximately equal to the excurrent pumping speeds of each species; dynamic pressure rather than viscous entrainment is probably the relevant factor determining reorientation behavior.
Dinosaur eggs: gas conductance through the shell, water loss during incubation and clutch size
Authors: Seymour Roger S. 
Published: July 2016

The conductance of water vapor and respiratory gases by diffusion through the eggshells of Upper Cretaceous dinosaurs has been estimated from measurements of shell and pore geometry in fossil specimens. When compared to recent reptile and bird eggs for which nest environments are known, the highly porous eggshells of three dinosaur species indicate that the dinosaur nests were high in humidity and probably low in oxygen and high in carbon dioxide. Such conditions most likely occurred underground or within an incubation mound.By isolating the eggs from the atmosphere, however, some large sauropods may have been forced to limit their clutch size to numbers small enough to prevent depletion of oxygen and elevation of carbon dioxide to intolerable levels in the nest. Fossil evidence supports this and suggests that one sauropod actually divided her large eggs into several clutches. Each small clutch probably had a metabolic rate similar to those of clutches produced by recent reptiles and mound nesting birds.
Escalating herbivory and resulting adaptive trends in calcareous algal crusts
Authors: Steneck Robert S. 
Published: July 2016

Evolutionary changes in herbivore abundance, diversity, and ability to excavate calcareous substrata occurred independently in three major herbivore groups: mollusks, urchins, and fish. These changes in herbivory have escalated dramatically since the mid-Mesozoic Era to the extent that herbivory today is more intense than at any time in the past.Today, calcareous red algal crusts (i.e., corallines) are a conspicuous and frequently dominant element of shallow marine communities. Corallines and their (assumed) parent taxon, solenopores, probably always required grazing to remain free of epiphytes. The large scale evolutionary trend toward increased grazing intensity may have given the corallines a distinct advantage over the more herbivore-susceptible solenopores. Four anatomical characters unique to corallines may have facilitated their rapid expansion into shallow reef environments and subsequently (more than 100 million years later) allowed them to withstand the more intense levels of grazing that evolved in those environments. Today corallines are the only algal form to thrive under, and often even require, intensive herbivory. The extinction of solenopores and the adaptive radiation of corallines parallel a gradient of escalating herbivory over time.Herbivores capable of excavating calcareous substrate are also frequently capable of denuding, and preventing the establishment of, stands of large leathery (kelp-like) macrophytes. It is possible that large-scale increases in herbivory have caused large-scale reduction of algal biomass in benthic communities. The presence of algal forests especially in the Paleozoic and early Mesozoic Eras may be a new variable to consider in reconstructing paleoenvironments.
The earliest known ants: an analysis of the Cretaceous species and an inference concerning their social organization
Authors: Wilson E. O. 
Published: July 2016

The known Cretaceous formicoids are better interpreted from morphological evidence as forming a single subfamily, the Sphecomyrminae, and even a single genus, Sphecomyrma, rather than multiple families and genera. The females appear to have been differentiated as queen and worker castes belonging to the same colonial species instead of winged and wingless solitary females belonging to different species. The former conclusion is supported by the fact that the abdomens of workers of modern ant species and extinct Miocene ant species are smaller relative to the rest of the body than is the case for modern wingless solitary wasps. The wingless Cretaceous formicoids conform to the proportions of ant workers rather than to those of wasps (Figs. 1–2) and hence are reasonably interpreted to have lived in colonies.The Cretaceous formicoids are nevertheless anatomically primitive with reference to modern ants and share some key traits with nonsocial aculeate wasps. They were distributed widely over Laurasia and appear to have been much less abundant than modern ants.
The taphonomy of gastropod shell accumulations in large lakes: an example from Lake Tanganyika, Africa
Authors: Cohen Andrew S. 
Published: July 2016

An investigation of shell morphometrics of the prosobranch genusParamelaniafrom Lake Tanganyika shows striking contrasts between some live and dead populations from identical localities. Living populations and surficial dead shells were collected from 15 sublittoral-profundal localities along the east side of the lake. Interpopulation variability in this endemic gastropod is clinal (N-S) for several shell characters. Intrapopulation variability of dead shell populations frequently exceeds that of live populations. Distinctive morphs may be present in a local dead shell population which are absent in the live population from the same locality. However, the phenodeviant dead shell morphology may occur among live snails elsewhere in the lake. Phenodeviant shells may be encrusted, but are unabraded and show no preferred orientation.Radiocarbon ages of >2000 yr b.p. on dead phenodeviants suggest that surficial shell accumulations in Lake Tanganyika are strongly time-averaged. Although wave activity and biogenic concentration are important processes in Lake Tanganyika, neither is sufficient under modern lake conditions to account for these admixed assemblages. Winnowing andin situstratigraphic condensation during periods of lowered lake levels is the most likely explanation for the occurrence of phenodeviant surficial shells. This hypothesis is consistent with the observation that extensive shell lags are exposed on the lake floor in areas currently inhabited by the same snails.A model of biogeographic range fluctuations for particularParamelaniamorphs during the Holocene, in concert with lake level fluctuations, can account for the shell assemblages seen on the lake floor today. The complex history of these accumulations suggests that taphonomic admixtures may obscure the interpretation of evolutionary sequences in the lacustrine stratigraphic record.
Effects of late Cenozoic sea-level fluctuations on the bivalve faunas of tropical oceanic islands
Authors: Paulay Gustav 
Published: July 2016

The frequent late Cenozoic glacial ages were accompanied by sea-level falls of 100–150 m amplitude. These falls stranded the complex inner-reef platforms and lagoons of tropical Pacific islands, while outer-reef-slope habitats persisted, although displaced downslope. The effects of glacial regressions on bivalves were studied by examining the zonation of species across reef systems and species composition on tectonically uplifted islands, islands with, effectively, local low sea stands. I show that qualitative habitat loss (the stranding of inner-reef habitats) was responsible for the local extinction of about one-third of the bivalve species that inhabit central Pacific islands during high sea stands, whereas quantitative loss of habitat area and climatic effects were inconsequential. Soft-sediment habitats, and consequently soft-bottom bivalves, were more drastically affected by sea-level fluctuations than were hard-bottom habitats and bivalves.Although many bivalve species were extirpated in the central Pacific during low sea stands, they survived in the western Pacific, where the different geomorphology of many marine systems provided refugia for lagoonal species. Thus, a large proportion of Pacific bivalve species has very dynamic distributions, undergoing great range reductions and expansions with falls and rises of sea level, and much of the present central Pacific lagoonal fauna is of Holocene age. Several implications of these findings are discussed.
Nonprogressive evolution in a clade of CretaceousMontastraea-like corals
Authors: Budd Ann F. , Coates Anthony G. 
Published: July 2016

A phylogeny of CretaceousMontastraea-like corals was constructed and used to evaluate the importance of differential speciation, selective extinction, and developmental constraints in the evolutionary history of the clade. Colonies assembled from localities across the central and western Tethyan region were subdivided into four stratigraphic levels: (1) Neocomian to lower Albian, (2) upper Albian to Cenomanian, (3) Turonian to Campanian, and (4) Maastrichtian. Ten corallite characters were measured on transverse thin sections of each colony, and analyzed following a three-step procedure: (1) species were recognized using all-inclusive average linkage cluster analyses (UPGMA) and a series of iterative canonical discriminant analyses; (2) species were separated by stratigraphic level and linked between levels by comparative analysis of the resulting discriminant scores; and (3) ancestor-descendant relationships were interpreted within and among adjacent levels using phenetic and cladistic approaches. A composite tree was then examined with respect to biogeography.The results suggest that a total of 16 species existed during the Cretaceous, only 2 of which extended between stratigraphic levels. Speciation events between levels 1 and 2 were associated with the radiation of “small-corallite” forms from a “large-corallite” form, as its distribution expanded southward into the Tethyan realm. Limited speciation and stasis predominated among species within the clade between levels 2 and 3. Speciation events between levels 3 and 4 were associated with the radiation of predominantly “large-corallite” forms from a “small-corallite” form, as the clade became restricted to the Caribbean. Extinction initially focussed on “small-corallite” forms, but later shifted to “large-corallite” forms. Morphologic change was constrained between two extremes, the lower limit of which involved a minimum corallite diameter possibly set by developmental or ecological constraints, and the upper by limitations to increases in number of septa. The overall net result was that of nonprogressive evolution within the clade.
The paradox of the first tier: an agenda for paleobiology
Authors: Gould Stephen Jay 
Published: July 2016

Nature's discontinuities occur both in the hierarchical structuring of genealogical individuals and in the distinct processes operating at different scales of time, here called tiers. Conventional evolutionary theory denies this structuring and attempts to render the larger scales as simple extrapolation from (or reduction to) the familiar and immediate—the struggle among organisms at ecological moments (conventional individuals at the first tier). I propose that we consider distinct processes at three separable tiers of time: ecological moments, normal geological time (trends during millions of years), and periodic mass extinctions.I designate as “the paradox of the first tier” our failure to find progress in life's history, when conventional theory (first tier processes acting on organisms) expects it as a consequence of competition under Darwin's metaphor of the wedge. I suggest a resolution of the paradox: whatever accumulates at the first tier is sufficiently reversed, undone, or overriden by processes of the higher tiers. In particular, punctuated equilibrium at the second tier produces trends for suites of reasons unrelated to the adaptive benefits of organisms (conventional progress). Mass extinction at the third tier, a recurring process now recognized as more frequent, more rapid, more intense, and more different than we had imagined, works by different rules and may undo whatever the lower tiers had accumulated.