bluuebunny/crossref_metadata_2025 huggingface dataset:
Economic Prospects for Sprinkle Irrigating Rice in Texas
Authors: Griffin Ronald C. , Rister M. Edward , Parker Michael R. , McCauley Garry N.
Published: July 2016

The economic feasibility of investing in sprinkler irrigation technology for rice production is investigated using linear programming and capital budgeting to identify the net annual benefits and net present value, respectively. Groundwater and both flat rate and volumetrically priced surface water sources of irrigation water are analyzed. Under typical practices occurring in rice production operations in the Texas Rice Belt, sprinkler irrigation technology is not profitable at current water costs. Producers using volumetrically priced surface water have the greatest incentive to consider sprinkler irrigation, but water prices must increase by over 250 percent for the investment in a sprinkler irrigation system to become attractive. Yield reductions associated with sprinkle-irrigated rice are a significant disincentive. For equivalent flood- and sprinkle-irrigated rice yields, an increase in water prices of over 175 percent is required before the investment in a sprinkler irrigation system becomes economically feasible.
Generic Advertising, Fob Price Promotion, and Fob Revenue: A Case Study of the Florida Grapefruit Juice Industry
Authors: Lee Jonq-Ying
Published: July 2016

Each year many agricultural commodity groups spend millions of dollars advertising and promoting generic products. Generic advertising of a number of farm commodities occurs under federal authorization, under separate legislation or under marketing orders, or it is funded by producers on a voluntary contribution or mandatory basis.

More than three-fourths of the advertising programs operating under separate federal legislation or marketing order authority have been initiated during the past ten years (Armbruster). In addition to existing advertising programs, several advertising programs authorized under federal legislation were voted down by producers in a referendum: the most recent case was a beef referendum.
Transportation Alternatives in Rural Communities: A Feasibility Analysis
Authors: Reinschmiedt Lynn L. , Murray Steven W.
Published: July 2016

Transportation is a vital element in our daily lives. Access to jobs, shopping, and other services depends upon some form of transportation. The principal means of transportation in the United States continues to be the automobile. Census figures show that in 1975, 84.7 percent of all workers in this country and 84.5 percent of the workers in non-metropolitan areas used the automobile to get to work (U.S. Bureau of the Census).
Implications of Feeder Pig Price Variability in Virginia Tele-Auction Markets
Authors: Baum Kenneth , Buccola Steven , Fisher Peter
Published: July 2016

During the last two decades, the feeder pig industry in Virginia has undergone significant growth in the number of pigs sold and in the value of total sales, along with improvement in marketing procedures. From 1959 to 1978, the number of feeder pigs sold in state-sponsored auctions increased from 2,195 to more than 150,000 per year (Virginia Department of Agriculture). Tele-Auction sales, conducted by the Virginia Feeder Kg Association, use a conference telephone system that allows distant buyers to bid for pigs described by lot size, grade, weight, and tail docking. Pigs from various producers are co-mingled into lots that are homogeneous with respect to these characteristics. The Tele-Auction system permits out-of-state buyers to participate easily in sales, thus increasing the demand for Virginia's feeder pigs. In 1979, the Association sponsored 128 sales at 8 locations.
Demand and Quality Uncertainty in Pecan Purchasing Decisions
Authors: Park Timothy A. , Florkowski Wojciech J.
Published: July 2016

A generalized Heckman model of purchase decisions incorporating perceived consumer quality attributes, ease of purchase, and familiarity with marketing outlets as factors influencing pecan purchases is estimated. Marketing efforts that encourage consumers to expand expenditures on nut products increase both the probability of pecan purchases and the amount purchased. Consumers who use all types of nuts in a wider variety of foods tend to purchase pecans more frequently. A diverse set of marketing outlets provides consumers with convenient sources for purchasing pecans and has a significant influence on the probability of pecan purchases but not the amount of pecans purchased.
An Economic Analysis of a Corn-Soybean Crop Rotation Under Various Input Combinations in South Central Texas
Authors: Funk Robert D. , Mjelde James W. , Hons Frank M. , Saladino Vince A.
Published: July 2016

Eight input combinations of commercial fertilizer, insecticides, and herbicides on a corn-soybean crop rotation in the Brazos River Bottom of Texas are evaluated. Input combinations which do not fully utilize all three inputs are consistently ranked higher by all criteria as the preferred input strategy for the corn-soybean rotation system. These results, which indicate limited input crop rotations that fall somewhere between the extremes of conventional agricultural production and organic agriculture, deserve further attention as a possible production alternative.
Conservation Tillage and Pesticide Use in the Cornbelt
Authors: Fuglie Keith O.
Published: July 2016

Adoption of conservation tillage can lead to substantial environmental benefits from reduced soil erosion. But benefits may be partially offset if adoption increases reliance on agricultural chemicals. Using area study data from the Cornbelt, this study examines factors affecting adoption of no-till and other conservation tillage systems and their effect on chemical use and corn yield. The results find no evidence that herbicide or fertilizer application rates are higher on fields with conservation tillage systems compared with conventional tillage. However, insecticide use may increase somewhat and yield may be lower. Current demographic trends in U.S. agriculture favor continued diffusion of conservation tillage.
Seafood through time: changes in biomass, energetics, and productivity in the marine ecosystem
Authors: Bambach Richard K.
Published: July 2016

The biomass of marine consumers increased during the Phanerozoic. This is indicated by the increase in both fleshiness and average size of individuals of dominant organisms, coupled with the conservative estimate that dominant organisms in the Cenozoic are at least as abundant as those in the Paleozoic. As faunal dominants replaced one another during the Phanerozoic the general level of metabolic activity increased due to both increase in basal metabolism and increase in more energetic modes of life. This demonstrates that the expenditure of energy by marine consumers has increased with time as well. There is a time lag in the expansion of more energetic life habits from environmental settings known to have high food supply into regions expected to have lower rates of food supply (e.g., bivalves into offshore carbonate environments or deep burrowing deposit feeders into the full range of shelf environments), and a time lag in diversification of energetic modes of life (e.g., predation or deep burrowing deposit feeding) for long intervals after they first appeared. This suggests that the supply of food increased across the whole spectrum of marine habitats during the Phanerozoic. The great diversification of specialized predators especially suggests that biomass increase took place all the way down the food chain to the level of primary production. The development of plant life on land and the impact of land vegetation on stimulating productivity in coastal marine settings, coupled with the transfer of organic material and nutrients from coastal regions to the open ocean, and the increase through time in diversity and abundance of oceanic phytoplankton all point to increased productivity in the oceans through the Phanerozoic.
A possible mechanism in convergent evolution
Authors: Jeppsson Lennart
Published: July 2016

It has been shown in laboratory experiments that viruses can transfer DNA from the host cell to other cells and even to those of another species. In nature such transfers could facilitate convergent evolution. Studied cases of convergent evolution indicate that a gene might be successfully transferred to another species to produce a similar phenotypic effect as frequently as once per 1–10 ma and the effects of gene transfer on evolution in general are likely to be considerable. There are many constraints on the cases of convergent evolution that might be considered as possible examples of gene transfer. First, both co-occurrence in space and time of the taxa in question and presence of complete reproductive isolation must be assessed. Further, both the limited space available in a virus particle and the necessity that the transferred DNA functions well in both mitosis and meiosis in heterozygotic individuals indicate that only rather short pieces of DNA would be expected to be transferred. This limits the possible effects of any gene transfer. Examples of convergent evolution in five Siluro-Devonian conodont lineages are briefly presented and assessed in terms of possible mechanisms of convergence.
Geometric regularity of some oblique sculptures in pectinid and other bivalves: recognition by computer simulations
Authors: Hayami Itaru , Okamoto Takashi
Published: July 2016

The geometric regularity of oblique sculptures in pectinids and some other bivalves was examined both theoretically and empirically. Camptonectes microsculpture occurs exclusively on the external surface of foliated calcite, and is well characterized by an invariably orthogonal relation to growth increments and almost uniform density over the surface. It is genetically unrelated to radial and other sculpturing. According to our SEM observations, its divergent orientation seems to be controlled primarily by the growth of calcite laths. In contrast, the shagreen microsculpture of pectinids is characterized by a quincunx arrangement of scales on the diagonal network. Shagreen microsculpture can be regarded as a variant of diagonal sculpture together with the simple oblique, divaricate, V-shaped, and zigzag patterns that are widespread in other bivalves. The geometric regularity of these variations as well as their mutual relationship can be readily recognized by computer simulations. All of these diagonal sculptures may result from interference between radial and commarginal elements. The formation of diagonal sculptures seems to occur by the periodic activation of regularly arranged sculpture-producing cells on the mantle margin.
On the heterocercal tail in sharks
Authors: Thomson Keith Stewart
Published: July 2016

A new account of the mechanical action of the heterocercal tail in fishes is given, developed from study of the swimming of sharks. The heterocercal tail is capable of delivering a thrust that can be oriented in a wide range of angles in the vertical plane. The orientation results from a balance of forces acting in the tail. Normally the heterocercal tail delivers neither an epibatic nor a hypobatic thrust, but rather one directly through the center of gravity of the fish. On the basis of the new account, predictions concerning the shape and proportions of the heterocercal tail are made and tested.
Apparent versus real biotic effects of transgressions and regressions
Authors: Jablonski David
Published: July 2016

In evaluating the biotic effects of transgressions and regression, care must be taken to ensure that observed patterns are not simply an artifact of the location of available stratigraphic sections along an ancient onshore-offshore gradient of adaptive types. Analysis of Recent bivalves suggests that very nearshore benthic assemblages are dominated by species that are geographically more widespread, are more eurytopic, and more often have planktotrophic larvae than species in offshore assemblages (Jackson 1974; Jablonski and Valentine 1980); this pattern may serve as a null hypothesis for paleobiogeographic analysis. Late Cretaceous bivalve and gastropod faunas of the Gulf and Atlantic Coastal Plain exhibit decreasing levels of endemism and increasing mean geographic range over the course of regression and return to high levels of endemism and low mean geographic range with the succeeding transgression. In addition, species with longer durations are more frequent at peak regression, while geologically shorter-lived species are more prevalent at peak transgression. As seen in Recent examples, the molluscan assemblages from nearshore facies have a higher proportion of species with broad environmental tolerances and planktotrophic larvae, and thus more extensive geographic and stratigraphic ranges, than do the more offshore shelf assemblages. Because late regressive phases are represented only by very nearshore facies, these directional changes in biogeographic and evolutionary characteristics are most parsimoniously interpreted as a reflection of the nature of the facies available for sampling rather than biotic effects of transgression and regression.
Variability in the formation and detection of growth increments in bivalve shells
Authors: Hughes Walter W. , Clausen Conrad D.
Published: July 2016

Growth increments in bivalve shells have been used in geophysics and paleoecology. However, little study has been given to the variability of increment patterns within and between shells. The variability of increment patterns is examined visually and quantitatively, with the help of a serial correlation computer program. Analyses of increment patterns of the bivalvesChione fluctifragaandProtothaca staminea(Veneridae) indicate that: 1) quantitative results complement the visual observations; 2) increments are not consistently detected during successive measurements; 3) a striking similarity exists between right and left valves of the same specimen; and 4) different specimens collected from the same natural environment do not show any one-to-one increment relationship—however, increment width trends may be present. The variation of increment patterns seen between specimens suggests caution in the use of bivalve increments in paleoecology.
The effects of temperature change and domestication on the body size of Late Pleistocene to Holocene mammals of Israel
Authors: Davis Simon J. M.
Published: July 2016

Size variation among several species of large mammals is examined both throughout a wide geographical range today and within the Late Pleistocene-Holocene archaeo-faunal sequence of Israel. A regression of log dental size on environmental temperature produces similar negative slopes for recent Palaearctic foxes, wolves and boars as well as for Nearctic foxes. These species, and others which also exhibit an inverse correlation between size and temperature today, became dwarfed at the end of the Pleistocene in Israel. Abundant fossil gazelle and fox mensural data indicate that this diminution coincided with the temperature elevation 12,000 yr ago. Both the similarity of regression slopes for the recent material and the temporal coincidence of dwarfing among fossil species, representing different ecologies, strongly implicate temperature as the main body-size determining factor. Changes evidenced in the fossil record for boar, wolf and fox approximate a 15°C temperature change (Δt) based on their respective present-day size-temperature regressions. This Δt, if taken as an estimate for the eastern Mediterranean, is considerably higher than generally accepted values.

An additional size reduction of aurochs, wolf and boar at the end of the Pleistocene or several millenia later is associated with their domestication. It may reflect man's preference for a large “head count” over individual large body size.
Skeletal Overgrowths Among Epizoans from the Silurian (Wenlockian) Waldron Shale
Authors: Liddell W. David , Brett Carlton E.
Published: July 2016

Substrata for numerous epizoans in the Silurian Waldron Shale were provided by the toppled and overturned calyces of camerate crinoids. These were inhabited by a skeletonized fauna consisting of at least 25 species; including several bryozoans, tabulates, inarticulate brachiopods, worms, and echinoderms.

Many of the encrusting bryozoans exhibit skeletal overgrowths which appear to reflect competitive interactions for space. Coexistence of certain of the bryozoans involved in such interactions is suggested by skeletal features such as inflated growth forms and upturned margins at junctions between colonies (both representing attempts to avoid being overgrown). In addition, the occurrence of overgrowth reversals within individual encounters indicates contemporaneity of that pair. Species may be ranked according to their relative overgrowth success; however, this ranking is far from rigid as lower ranked species may on occasion overgrow more highly ranked species. Such nontransitive patterns appear similar to those described from Recent cryptic bryozoan faunas.
A Turn in the Right Direction: Simulation of Erect Spiral Growth in the BryozoansArchimedesandBugula
Authors: McKinney Frank K. , Raup David M.
Published: July 2016

Colonies of the fossil bryozoanArchimedesand erect, spiralled species of the living bryozoanBugulaconsist of wedge-shaped systems of radially diverging, bifurcated branches that extend from a helical axial margin. Morphology of these colonies may be simulated using few growth rules. These include 1) radius of the central helical margin (RAD), 2) rate of climb of central helical margin (ELEV), 3) radial angle between successive branches that originate from the central helical margin (ANG), 4) radial growth of all branches, 5) angle between branches and axis of central helical margin (BWANG), 6) distance between three adjacent, radially diverging branches at which the central branch bifurcates into two branches equally spaced between the two side branches (XMIN), and 7) placement of a spacing bar at base of newly bifurcated branches. In addition, size constraints on the simulations must be stipulated.

Simulations are begun at a proximal point along the central helix where a radial branch originates and are “grown” in repetitive steps by extending the central helical margin a distance distally, determined by ANG, then censusing established branches for XMIN in order to bifurcate appropriate branches and extend others in several short growth increments, etc. Growth of branches ceases at stipulated maximum width, and growth of the entire simulation ceases at stipulated maximum height.

The presence of a helical inner margin marked by uniformly spaced bifurcations generates the spiralled shape, i.e. ELEV must be a positive number. Values of RAD, ELEV (not zero), ANG and BWANG determine form of the spiral; the other growth rules apply to bifurcated unilaminate branch systems in general.

The range of observed colony forms and hypothetical morphospace ofArchimedesmay be simulated by varying BWANG, XMIN, and ELEV. RAD was kept constant, as its variation would be redundant with XMIN and ELEV. Variation in ANG affects near-helix morphology, but its influence is undetectable beyond this zone. Variability within colonies may be simulated by assigning to each variable a standard deviation with mean-centered randomly chosen values for each decision.
The Theory of Evolution by Natural Selection: A Hierarchical Expansion
Authors: Arnold Anthony J. , Fristrup Kurt
Published: July 2016

Alleles, individuals, and species are all examples of entities possessing variation in the properties that underlie natural selection: branching (reproduction), persistence (survivorship), and heritability of characters. This suggests that the logic embodied in the theory of natural selection can be abstracted from its usual application to the level of individuals to encompass selection operating among any biological entities for which these essential properties can be meaningfully defined. This approach leads to a unified perspective of adaptation, selection, and fitness at all levels. Expanded versions of the Price covariance selection equations provide a convenient and useful conceptual vehicle for this discussion. The advantages of a hierarchical approach are twofold: it permits exploration of concepts and ideas across levels by analogy, and it focuses attention upon the mechanisms that account for different evolutionary dynamics at each level rather than obscuring these biologically unique properties with argument by extension from a single “special” level.

We point out that the choice of a single measure of evolutionary change restricts the context in which “other level” processes will be perceived. We illustrate the limited forms in which higher and lower level selection can be recognized from the unique perspective provided by any given level through extensions of Price's formula.

An exploration of the implications of such an approach leads us to the assertion that the development of a unified theory of evolution demands the recognition and incorporation of hierarchical structure as a conceptual foundation.
Infaunal survival: alternative functions of shell ornamentation in the Bivalvia (Mollusca)
Authors: Stanley Steven M.
Published: July 2016

Two kinds of adaptation aid infaunal bivalve mollusks in sustaining their life positions against potentially disruptive water movements: (1) ability to retard scour of surrounding sediment and (2) ability to reburrow rapidly if exhumed.

The shell of the venerid Anomalocardia brasiliana is ornamented with concentric ridges that are asymmetrical in cross-section; experiments show that these ridges aid the animal in burrowing by gripping the sediment during backward rotation of the shell. The shell of the less deeply burrowing venerid Chione cancellata also bears concentric ridges, but these are symmetrical and experiments show that they hinder burrowing; other experiments demonstrate that these ridges reduce scour of sand from around a partly exposed animal. The single cardiid species Trachycardium egmontianum possesses adaptations comparable to those of the two venerid species, in the form of spines of two varieties; experiments show that the flared anterior spines facilitate burrowing and the cupped posterior spines reduce scour.

Conspicuous ornamentation of the kinds considered here was rare throughout the Paleozoic. Its evolutionary deployment occurred primarily during the post-Paleozoic adaptive diversification of infaunal bivalves, which was triggered by the evolution of efficient burrowing mechanisms. The general premium on maintaining infaunal life positions was accentuated for bivalves after the Paleozoic by the origins of important modern predatory taxa.
Arm movement and feeding mode of inadunate crinoids with biserial muscular arm articulations
Authors: Lane N. Gary , Burke J. J.
Published: July 2016

True muscular articulations, as opposed to ligamentary ones, are reported here for the first time in the biserial arms of advanced inadunate crinoids (Poteriocrinina). The topography of biserial articular surfaces indicates clearly derivation from a uniserial muscular articulation with two muscle scars, a transverse ridge, and other structures considered typical of this articular mode. Biserial muscular articulations extend from the arm base to within a few brachials of the arm tip, although the articulations are more pronounced and better developed proximally. The inadunate facets are compared with those of the biserial arms of camerates, which are shown to be non-muscular and probably were capable of only limited movement. The arm movements of inadunate biserial arms are interpreted to have been ones where alternating muscle bundles on either side of the arm induced twisting motions of the arms so that a planar filtration fan mode of feeding was possible, in contrast to the parabolic feeding fan or other modes of feeding that were probably performed by other Paleozoic crinoids.
Mammalian faunal dynamics of the great American interchange
Authors: Webb S. David
Published: July 2016

The American interchange of land mammals reached its acme during the late Blancan and early Irvingtonian in North America and during the Chapadmalalan and Uquian in South America. It lasted about two million years and included taxa adapted to diverse habitats. It was preceded in the early Hemphillian in North America and the Huayquerian in South America by the interchange of a few heralding genera. The MacArthur-Wilson faunal equilibrium hypothesis correctly predicts a marked increase in originations, number of genera, and turnover rate for the South American fauna during the peak of the interchange. Subsequent further increases were not so predicted but closely resemble patterns also observed in late Pleistocene land mammals of Europe and North America. The continued increase in South American land mammal genera after the interchange had largely ceased resulted principally from autochthonous evolution of northern immigrant stocks. A marked decrease in South American ungulate genera (from thirteen to three) coincided with the appearance of fourteen northern ungulate genera and therefore appears to be a replacement phenomenon. The area/diversity relationship predicts no important change in generic diversity if a maximum of only nine percent of North America is occupied by the interamerican mingled fauna. At the family level, however, diversity is seriously overestimated due to the nomenclatural artifact of increased relative diversity by filtering.
Functional interpretation of lyre-shaped Bryozoa
Authors: McKinney Frank K.
Published: July 2016

Colonies of Late Paleozoic lyre-shaped fenestrate bryozoans began growth on rigid substrates which were on the sea floor. After production of a basal disc, a fenestrate network developed in the shape of an erect bowed fan. The fenestrate fan was initially concave on the apertural side, but the curvature reversed a few millimeters above the base. Colonies were then separated along or just above the basal disc, and rested directly on the sea floor. The zooecial apertures were directed upward. The lateral margin of the fan grew to form the supporting struts of the soon-to-be lyre-shaped colony. An open vault formed below the upwardly bowed fan.

Lyre-shaped colonies are interpreted to have lain on the sea floor so that each had the proximal end on the upcurrent side. Feeding zooids were on the upper surface and pulled water through their expanded tentacles. The filtered water passed through the fenestrules, into the vault, and out the open end of the vault, which was on the downcurrent side.
Functional significance of spines in the Pennsylvanian horseshoe crabEuproops danae
Authors: Fisher Daniel C.
Published: July 2016

Euproops danae, a xiphosuran from the Mazon Creek (Braidwood) Fauna, had two sets of spines—genal and ophthalmic—extending from the posterior margin of its prosoma. In young individuals, the genal spines were longer than the ophthalmic spines. During growth, the relative length of each type of spine increased, but the rate of increase was much greater for ophthalmic spines. In order to explain these morphological and ontogenetic features, I have studied the hydrodynamic behavior of whole-animal models representing the actual morphology ofE. danae, and various modifications thereof, at different body sizes. It can be argued that passive settling, while in an enrolled posture, was probably the primary defensive reaction that a swimming individual would have exhibited in response to an encounter with a potential predator. Experiments show that the array of spines onE. danaewas an important control on the style of settling experienced by an enrolled individual. Models of the actual morphology settle steadily, while models with either longer or shorter prosomal spines tend to undergo lateral oscillations induced by turbulence in the wake. Steady fall would have rendered the horseshoe crab less perceptible to either the visual or lateral line systems of contemporary aquatic vertebrates, and thus a morphology capable of producing it would have been an important adaptation for reducing the risk of predation. This minimization of oscillatory movement would actually obtain for a variety of conceivable spine morphologies, but actual morphologies represent those ‘solutions’ which simultaneously optimize other aspects of spine function, such as mechanical protection. This optimum design changes during ontogeny because settling dynamics scale non-linearly with size. This work has both specific applications to the interpretation of similar structures in other arthropods and more general implications for the study of evolutionary functional morphology.
Some “laws” of gastropod shell form
Authors: Linsley Robert M.
Published: July 2016

Five generalizations derived from the shell form of prosobranch gastropods are developed. (1) A univalve of more than one volution whose aperture lies in a plane that passes through the axis of coiling does not live with the aperture parallel to the substrate. (2) A univalve of more than one volution whose aperture lies in a plane that is tangential to the body whorl does live with the plane of the aperture parallel to the substrate. (3) Gastropods with tangential apertures, when extended, support the shell so that the center of mass of the shell and its contents is over the midline of the cephalopedal mass; this balancing of the shell may be accomplished either by regulatory detorsion, by inclination or by a combination thereof, to keep the center of gravity of the shell as low as possible. (4) Angulations or re-entrants in the gastropod aperture are usually indicative of inhalent or exhalent areas; inhalent areas are directed as far anteriorly as possible. (5) Gastropods having elongated apertures possess only a single gill and develop a water current through the mantle cavity from anterior to posterior along the long axis of the aperture; this axis is subparallel to the anterior-posterior axis of the foot.

These generalizations are then used as the basis for some deductive interpretations of behavioral modes of Paleozoic Gastropoda.
The Mesozoic marine revolution: evidence from snails, predators and grazers
Authors: Vermeij Geerat J.
Published: July 2016

Tertiary and Recent marine gastropods include in their ranks a complement of mechanically sturdy forms unknown in earlier epochs. Open coiling, planispiral coiling, and umbilici detract from shell sturdiness, and were commoner among Paleozoic and Early Mesozoic gastropods than among younger forms. Strong external sculpture, narrow elongate apertures, and apertural dentition promote resistance to crushing predation and are primarily associated with post-Jurassic mesogastropods, neogastropods, and neritaceans. The ability to remodel the interior of the shell, developed primarily in gastropods with a non-nacreous shell structure, has contributed greatly to the acquisition of these antipredatory features.

The substantial increase of snail-shell sturdiness beginning in the Early Cretaceous has accompanied, and was perhaps in response to, the evolution of powerful, relatively small, shell-destroying predators such as teleosts, stomatopods, and decapod crustaceans. A simultaneous intensification of grazing, also involving skeletal destruction, brought with it other fundamental changes in benthic community structure in the Late Mesozoic, including a trend toward infaunalization and the disappearance or environmental restriction of sessile animals which cannot reattach once they are dislodged. The rise and diversification of angiosperms and the animals dependent on them for food coincides with these and other Mesozoic events in the marine benthos and plankton.

The new predators and prey which evolved in conjunction with the Mesozoic reorganization persisted through episodes of extinction and biological crisis. Possibly, continental breakup and the wide extent of climatic belts during the Late Mesozoic contributed to the conditions favorable to the evolution of skeleton-destroying consumers. This tendency may have been exaggerated by an increase in shelled food supply resulting from the occupation of new adaptive zones by infaunal bivalves and by shell-inhabiting hermit crabs.

Marine communities have not remained in equilibrium over their entire geological history. Biotic revolutions made certain modes of life obsolete and resulted in other adaptive zones becoming newly occupied.
On the measurement of size-independent morphological variability: an example using successive populations of a Devonian spiriferid brachiopod
Authors: Flessa Karl W. , Bray Ron G.
Published: July 2016

More than 500 undistorted, unfragmented pedicle valves of Ambocoelia umbonata (Conrad) (Spiriferida, Brachiopoda) were recovered from each of four levels within a Middle Devonian fossil cluster. The fossil cluster, an ellipsoidal shell accumulation measuring one meter in diameter and 2 cm in thickness, was exhumed from an exposure of the Ludlowville Shale (Hamilton Group) of western New York. Size frequency histograms indicate that the brachiopod experienced very high levels of juvenile mortality, due, probably, to the effects of high bottom turbidity. Sedimentological and paleontological evidence indicates that the cluster represents a sequence of in situ benthic associations.

Size-independent variation was estimated by calculating the eigenvalue of the minor axis on a log-transformed plot of pedicle valve lengths and widths. The eigenvalue technique eliminates the effect of allometrically induced shape changes and is applicable to multicharacter analyses of morphological variability.

Size-independent variability among the larger individuals of Ambocoelia decreases in successively younger cluster populations. The decrease is not correlated with any observed or inferred change in substratum, diversity, equitability or turbidity.
Formation and paleontologic recognition of structures caused by marine annelids
Authors: Ronan Thomas E.
Published: July 2016

Laboratory and field collected sediments were x-rayed to document the array of biogenic sedimentary structures produced by the burrowing and feeding behavior of six species of marine intertidal annelid (Glycera robusta, Nephtys caecoides, Pectinaria californiensis, Notomastus magnus, Eupolymnia crescentis, and Cirriformia spirabrancha). Polychaete burrows were found to vary greatly in structural complexity with both errant (N. magnus) and relatively sessile forms (C. spirabrancha) producing a variety of biogenic structures. Sediment mixing by the tentacle-feeding polychaete C. spirabrancha was observed by sequentially x-raying an experimental field enclosure stratified with an opaque substance. The experiment demonstrates that tentacle-feeding polychaetes can influence the topography of the sediment-water interface and transport substantial amounts of near surface material downward.

Criteria by which fossil biogenic sedimentary structures, presumably produced by soft-bodied organisms, can be assigned a feeding function have been advanced by Walker (1972). Some of the assumptions inherent in feeding function analysis were applied, with varying degrees of success, to the biogenic structures of modern soft-sediment polychaetes.
Reconstructing mammalian communities: a discussion of Shotwell's method of paleoecological analysis
Authors: Grayson Donald K.
Published: July 2016

Shotwell's method of paleoecological reconstruction attempts to define community membership of mammals represented within paleontological assemblages. Analysis of the measure of community membership upon which the method is based (relative skeletal completeness) shows this measure to be a function of sample size. A method for controlling for the effects of sample size upon measures of relative skeletal completeness is needed. A method is suggested which employs ratios of numbers of individuals to numbers of specimens, and a specific correction of Shotwell's method is proposed.
Flume study of simulated feeding and hydrodynamics of a Paleozoic stalked crinoid
Authors: Welch James R.
Published: July 2016

Life-sized scale models and a flume were used to observe simulated feeding and hydrodynamics of the Paleozoic camerate crinoid, Pterotocrinus. Three orientations of the crown and filtration fan (downcurrent, upcurrent, upright) in a gentle (3.5 cm/sec) current were used. Maximum baffling of the current and eddying of water into feeding areas occurred where models were oriented like most living stalked crinoids, with a parabolic filtration fan perpendicular to the current and ambulacral side downcurrent. Facing the ambulacral side of the fan upcurrent reduced time available for entrapment of potential food particles. Calyx shape was important in modifying the nature of the filtration fan baffle. Overlapping (36%) of the pinnulate arms increased the baffling effect of the filtration fan. Conspicuous tegminal structures, the Pterotocrinus wing plates, only had a baffling effect where the fan was in an upright position or the arms were infolded between the wing plates. Species of Pterotocrinus possessing blade-like wing plates could have fed effectively in several different orientations. Evolutionary success of Pterotocrinus species with blade-like wing plates probably resulted from dual feeding and protective functions of the wing plates.
Mode of life of planktonic graptolites: flotation structure in Ordovician Dicellograptus sp.
Authors: Finney Stanley C.
Published: July 2016

An unusual isolated specimen representing an immature rhabdosome of Dicellograptus sp. from the Middle Ordovician Athens Shale of Alabama has a flattened sphere attached to the distal end of the nema. The flattened sphere can be interpreted as a float that probably conferred buoyancy on the rhabdosome. Such floats, which became detached in mature rhabdosomes, may be common in the fossil record. The presence of nematophorous siculae in all planktonic graptolites suggests that for immature rhabdosomes a passive, buoyant mode of life, attained by means of a float, might have been widespread taxonomically. This mode of life is compatible with the theory of passive response for the mode of life of mature rhabdosomes, but it is difficult to reconcile with the theory of automobility.
A note on the estimation of species duration distributions
Authors: Gillespie John H. , Ricklefs Robert E.
Published: July 2016

The mathematical relationship between species survivorship and duration curves is derived using standard demographic arguments. The result, when applied to the late Cenozoic mammals, suggests that there was an inhomogeneity in the mammalian radiation just before the Wurm, or that the mammalian speciation process has not yet attained the stable-age distribution.
Constructional morphology of sand dollars
Authors: Seilacher Adolf
Published: July 2016

This paper analyzes an aberrant group of echinoids in terms of constructional morphology, i.e., as modification of an established “Bauplan” by a set of new functional and morphogenetic constraints and possibilities. The characteristics of sand dollars (flat test, spine differentiation, branched food grooves, lunules) are related to a particular combination of burrowing and sieve feeding in sandy sediments. It has independently evolved from less specialized Clypeasteroids in at least three lineages (Scutellina, Rotulidae, Arachnoididae), which have solved inherent problems differently (sutural interlocking; growth patterning of food grooves and canal systems; lunule formation; weight belts). These three groups have radiated in different degrees due to their different palegeographic histories.
The relationship of the scleractinian corals to the rugose corals
Authors: Oliver William A.
Published: July 2016

The Mesozoic-Cenozoic coral Order Scleractinia has been suggested to have originated or evolved (1) by direct descent from the Paleozoic Order Rugosa or (2) by the development of a skeleton in members of one of the anemone groups that probably have existed throughout Phanerozoic time. In spite of much work on the subject, advocates of the direct descent hypothesis have failed to find convincing evidence of this relationship. Critical points are:

(1) Rugosan septal insertion is serial; Scleractinian insertion is cyclic; no intermediate stages have been demonstrated. Apparent intermediates are Scleractinia having bilateral cyclic insertion or teratological Rugosa.

(2) There is convincing evidence that the skeletons of many Rugosa were calcitic and none are known to be or to have been aragonitic. In contrast, the skeletons of all living Scleractinia are aragonitic and there is evidence that fossil Scleractinia were aragonitic also. The mineralogic difference is almost certainly due to intrinsic biologic factors.

(3) No early Triassic corals of either group are known. This fact is not compelling (by itself) but is important in connection with points 1 and 2, because, given direct descent, both changes took place during this only stage in the history of the two groups in which there are no known corals.
Competitive exclusion in evolutionary time: the case of the acorn barnacles
Authors: Stanley Steven M. , Newman William A.
Published: July 2016

Barnacles living along rocky shores provide the classic example of competitive dominance in the marine ecosystem: by means of firm attachment and rapid growth, balanoid barnacles commonly undercut and overgrow the genus Chthamalus, which is thereby restricted to the upper fringe of the intertidal zone, where balanoids are physiologically incapable of living. Today, after perhaps less than 50 Myr of evolution, balanoid barnacles are in the midst of rampant adaptive radiation, being represented by about 273 species, of which about half are free-living species of intertidal or shallow subtidal habitats. Chthamaloid barnacles, in contrast, are on the decline, having originated at least 70 Myr ago but today comprising only about 53 living species, approximately 40 of which occupy the uppermost intertidal. The remainder persist as localized, relict, and often disjunct populations. Through competitive exclusion, balanoid barnacles have apparently caused the ecological restriction and decline of the chthamaloids. The balanoids have an advanced feeding mechanism, but the most important adaptive breakthrough leading to their competitive success was probably the origin of a tubiferous wall structure, which affords rapid skeletal growth for the efficient monopolization of free space and for the destruction of chthamaloids.
Bivalve Species Duration, Areal Extent and Population Size in a Cretaceous Sea
Authors: Koch Carl F.
Published: July 2016

Geographic distribution, species duration, and population size of 41 bivalve species which coexisted during the uppermost biozone (Sciponoceras gracile zone) of the Cenomanian were measured. Average species duration and correlation between geographic distribution, species duration, and population size were computed for five groups: total, infaunal, epifaunal, cemented epifaunal, and uncemented epifaunal bivalves.

Average species duration for all bivalves is less than 2 Myr. Infaunal bivalves averaged slightly higher, epifaunal slightly lower. Positive correlation was measured between species duration and geographic distribution for all five groups and statistical significance of the relationships was demonstrated for all but infaunal forms. In general no correlation was found between species duration and population size, and between population size and geographic distribution with the following exceptions: species duration and population size were significantly correlated for infaunal bivalves and uncemented epifaunal bivalves, and population size and geographic distribution were correlated for uncemented bivalves. Because these 41 fossil species coexisted at the same time and were distributed in the same space, differences in the relationships of species duration, geographic distribution and population among the various life habits indicate differences in ecological strategy and the evolutionary consequences of that difference.
Influence of Larval Dispersal and Geographic Distribution on Species Longevity in Neogastropods
Authors: Hansen Thor A.
Published: July 2016

The Lower Tertiary Gulf Coast was subjected to repeated transgressive-regressive cycles of varying rate and extent which had a marked effect on species longevities. In some neogastropods dispersal and geographic distribution played important roles in species longevities. Species with planktic larval stages that inhabited broad areas of the Gulf Coast could maintain their distributions even during regressive phases when delta building was strong. Wide distributions, free gene flow, and resistance to isolation gave planktic species an evolutionary stability that resulted in greater species longevity. Species with nonplanktic development could attain wide geographic ranges when barriers were minimized, but they were unable to maintain their distributions in the face of regressive progradation. Thus their populations were isolated, and extinction and speciation accelerated, giving them lesser evolutionary longevity. Although planktic volutids tend to be widespread, planktic fasciolariids and mitrids were often restricted in distribution and therefore probably stenotopic. If dispersal and environmental tolerance are considered as separate forces, they seem to act in combination to produce very long, very short or intermediate species longevities.
Taphonomy and Paleoecology of the Dinosaur Beds of the Jurassic Morrison Formation
Authors: Dodson Peter , Behrensmeyer A. K. , Bakker Robert T. , McIntosh John S.
Published: July 2016

The Upper Jurassic Morrison Formation has yielded one of the richest dinosaur faunas of the world. Morrison sediments are distributed over more than a million square kilometers in the western United States and represent a mosaic of riverine, lacustrine and floodplain environments developed on a vast alluvial plain nourished by debris from the ancestral Rocky Mountains. Plant productivity must have been reasonably high to support abundant large-bodied herbivores, but the absence of coals, scarcity of small aquatic vertebrates, the abundance of oxidized sediments, and presence of calcretes lead us to believe that water was periodically in short supply. A strongly seasonal climate may have necessitated annual large-scale movements of large herbivores, accounting in part for their remarkably broad and uniform geographic distribution. Dinosaur diversity is lower in the Morrison than in the Late Cretaceous, and taphonomic alteration is higher. Massed accumulations of thousands of bones are characteristic of the Morrison. Morrison dinosaurs were not confined to specific depositional environments but were distributed across the complete spectrum of available habitats, from lakes to dry floodplains; this type of distribution is similar to that of large terrestrial mammals such as elephants and rhinos and is different from that of hippos and crocodiles. Common Morrison taxa wereCamarasaurus, Apatosaurus, Diplodocus, AllosaurusandStegosaurus;these genera probably constituted a true dinosaur community.Stegosaurusmay have been partially segregated from the other genera, andCamptosaurusmore strongly so.CamarasaurusandDiplodocuswere gregarious, with juveniles and subadults of the former particularly common;Apatosauruswas less abundant and more solitary in its habits. Juveniles and subadults are known for a number of dinosaurs.
Phyletic gradualism vs. punctuated equilibrium: applicability of neontological data
Authors: Ricklefs Robert E.
Published: July 2016

An equation for the distribution of divergence times between closest relatives is derived to explore the possibility that contemporary data might shed some light on the controversy between supporters of gradual versus punctuated phyletic change. The principal assumptions of the model are uniform rates of speciation and extinction, bifurcating speciation, and uniform patterns of divergence, by whatever measure, among species in a taxon. The structure of the model indicates clear differences between patterns generated by extremes of gradualism and punctuation. But inability to verify critical assumptions considerably weakens the applicability of the model to the gradualism-punctuation problem.