bluuebunny/crossref_metadata_2025_split huggingface dataset:
A model for planktic foraminiferal shell growth
Authors: Signes Miguel , Bijma Jelle , Hemleben Christoph , Ott Rolf 
Published: July 2016

In this paper we analyze the laws of growth that control planktic foraminiferal shell morphology. We assume that isometry is the key toward the understanding of their ontogeny. Hence, our null hypothesis is that these organisms construct isometric shells. To test this hypothesis, geometric models of their shells have been generated with a personal computer. It is demonstrated that early chambers in log-spirally coiled structures cannot follow a strict isometric arrangement. In the real world, the centers of juvenile chambers deviate from the logarithmic growth curve. Juvenile stages are generally more planispiral and contain more chambers per whorl than adult stages. These traits are shown to be essential in order to keep volumes of consecutive chambers in geometric progression. We are convinced that the neanic stage marks the constructional bridge from a juvenile set of growth parameters to an adult one. The adult stage can be strictly isometric, that is, the effective shape is constant and the increase in volume after a chamber addition is proportional to the preexisting volume of the shell.The shell volume is related to the biomass, the ratio of outer shell surface area to shell volume is related to the respiration rate and the ratio of the total shell surface area to shell volume is related to the total calcification effort. The influence of the parameters of the model on these relationships is investigated. Only the initial radius and the rate of radius increase affect the relationships between shell volume and surface area. The other shape parameters merely provide a fine tune-up of these relationships. Size itself plays a major role during foraminiferal development.
Disparity as an evolutionary index: a comparison of Cambrian and Recent arthropods
Authors: Wills Matthew A. , Briggs Derek E. G. , Fortey Richard A. 
Published: July 2016

Disparity is a measure of the range or significance of morphology in a given sample of organisms, as opposed to diversity, which is expressed in terms of the number (and sometimes ranking) of taxa. At present there is no agreed definition of disparity, much less any consensus on how to measure it. Two possible categories of metric are considered here, one independent of any hypothesis of relationship (phenetics), the other constrained within an evolutionary framework (cladistics).The Early Cambrian radiation was clearly a period of significant morphologic and taxonomic diversification. However, we question the interpretation of its first generation products as numerous body plans at the highest level. Four phenetic and two cladistic measures have been used to compare disparity among Cambrian arthropods with that in the living fauna. Phenetic methods assessing character-state variability and the amount of morphological attribute space occupied yield similar results for Cambrian and Recent arthropods. Assessments of disparity within a taxonomic framework rely on the identification of particular characters that delineate higher level body plans. This requires a phylogenetic interpretation, a cladistic investigation of hierarchical structure in the data. Both sets of arthropods fall within the same major clades, and within this cladistic framework the amount of character-state evolution in the two groups is comparable. None of these methods identifies markedly greater disparity among the Cambrian compared with the Recent taxa.Although measures of disparity are applied here to a consideration of the Cambrian radiation, the metrics clearly have a much wider potential for estimating macroevolutionary trends independently from existing taxonomic frameworks. Geometric morphometry is ideal for measuring morphological variety at lower taxonomic levels, but it requires the recognition of homologous landmarks in all the forms under comparison, or the identification of entire homologous structures. Conventional phenetics has much wider application as it can operate on data coded as discrete homologous character states (this facility is also a requirement of cladistics), which are a more appropriate basis for comparing disparity in markedly dissimilar forms.
Extinction selectivity and ecology of Neogene Caribbean reef corals
Authors: Johnson Kenneth G. , Budd Ann F. , Stemann Thomas A. 
Published: July 2016

We analyze a new compilation of Neogene to Recent (22-0 Ma) Caribbean coral occurrences to determine how ecological and life history traits at the population level affect long-term evolutionary patterns. The compilation consists of occurrences of 175 species and 49 genera in one continuous (> 5 m.y.) sequence and 22 scattered sites across the Caribbean region. Previous study of evolutionary rates using these data has shown that both extinction and origination were accelerated between 4 and 1 Ma, resulting in large-scale faunal turnover. Categories for three morphological and two reproductive variables (colony size, colony shape, and corallite size; and sex, and mode of embryonic development; respectively) are assigned to each species in the compilation. Comparisons of the ecological variables with evolutionary rates using randomization procedures and modified analysis of variance show that only colony size was strongly related to rates of extinction and origination during either normal background times or times of accelerated extinction. Extinction rates were lower in species with large colonies, because species with small massive colonies tend to live in small, short-lived populations with highly fluctuating recruitment rates. During turnover, extinction rates increased disproportionately in species with small colonies. Origination rates are found to be less related to ecological variables, although species with small massive colonies originated at higher rates prior to turnover.Accelerated turnover may have therefore involved an increase in local population extinction rates that caused increased rates of both species extinction and origination across the entire fauna. Since extinction rates accelerated disproportionately with respect to colony size, the overall result was a relative increase in species with large colonies. After severe disturbance, one might expect that populations of species with large colonies and high rates of fragmentation would be more likely to escape extinction, because of larger population sizes, longer generation times, and more constant rates of population increase. The modern Caribbean reef-coral fauna is therefore structured by large, long-lived colonies that are robust to regional environmental change. Many of the very taxa that allowed reef communities to escape collapse in the past are declining today in response to anthropogenic disturbances, suggesting that Caribbean reef communities may be less resilient in the future in response to ongoing environmental perturbations.
Diversity patterns among early gastropods: contrasting taxonomic and phylogenetic descriptions
Authors: Wagner Peter J. 
Published: July 2016

Paleobiologists have used taxonomic data for several types of diversity studies. Some systematists have charged that this practice obfuscates actual historical patterns of clades because many traditionally defined higher taxa are not monophyletic. Some have questioned whether ranked taxa ever represent comparable units, even when monophyletic. This study contrasts diversity patterns implied by phylogenetic estimates with those implied by ranked taxa. Early Paleozoic gastropods are useful as a test case because their generic taxonomy does not reflect the phylogenetic systematic philosophy, and fewer than one third of the genera represent monophyletic clades. Phylogenetic diversity is described in two ways: (1) numbers of lineages (i.e., observed plus phylogenetically implied “ghost lineages”), and (2) numbers of monophyla (i.e., clades whose sister taxa are other clades rather than species). “Monophyla” as tallied here are monophyletic relative to their contemporaries and older clades; however, they can be paraphyletic relative to “future” monophyla. Phylogenetic diversity is tallied with both maximum and minimum “ghost lineage” interpolations in order to reflect different possible speciation patterns and timings of speciation. Phylogenetic diversity as implied by a stricter cladistic criterion (i.e., taxa that are monophyletic relative to their contemporaries, older taxaandyounger taxa) is discussed also.First differences between substage-to-substage standing diversities reveal significant congruence between generic data and both types of phylogenetic data. Taxonomic and phylogenetic data imply a major extinction event at the end of the Ordovician, although the phylogenetic data suggest greater extinction levels than do the taxonomic data. Both data sets also suggest diversity-dependent diversification reminiscent of logistic growth, which is the pattern predicted if one or a few major ecologic factors were constraining the diversification of gastropods. However, diversity described by strict Hennigian taxa is not highly congruent with diversity as described by either lineages or monophyla. Comparing subclade dynamics requires extensive redefinition of traditional orders, but lineages, monophyla and genera all suggest that the two major subclades had different logistic diversification patterns, with one (“murchisonioids”) having a higherKthan the other (“euomphaloids”). The concern that phylogenetic and taxonomic data might imply very different evolutionary histories is not borne out by gastropods, despite the nonphylogenetic nature of their traditional taxonomy.
Taphonomy of mammalian fossil remains from Siwalik rocks of Pakistan
Authors: Badgley Catherine 
Published: July 2016

Siwalik rocks of Pakistan are a virtually continuous, continental sedimentary sequence, extending in age from 18 to 1 ma b.p. This paper describes taphonomic features of late Miocene mammalian assemblages from a highly fossiliferous interval about 400 m thick, based on field documentation of sedimentary environments at 42 fossil localities and systematic fossil collection of 21 localities.Within a broadly fluvial system, I recognize four sedimentary environments of bone accumulation, distinguished by lithology, unit-thickness, unit-geometry, contacts, sedimentary structures, and relationship to adjacent units. Each environment corresponds to an association of lithofacies. Facies Association I is interpreted as the persistent, major channel bodies of a meandering fluvial system; Facies Association II as coarse-grained flood deposits, such as crevasse splays, deposited beyond the main channels; Facies Association III as channel margins, including levees and swales; and Facies Association IV as predominantly subaerial floodplains.Taphonomic features of bone assemblages from each facies association include skeletal-element composition, surface distribution of specimens, degree of articulation, hydraulic equivalence between organic and inorganic sedimentary particles, frequency of juvenile remains, size distribution of fauna, and an estimate of duration of accumulation of individual fossil localities. The distribution of these features among the four facies associations suggests that bone assemblages in Facies Associations I and II accumulated by the action of currents in river channels or floods, whereas bone assemblages in Facies Associations III and IV accumulated through concentration by biological agents and/or attrition at a repeatedly used site of predation.Inclusion in fluvial accumulations depends on initial availability of skeletal remains and hydraulic characteristics of individual skeletal elements, but not taxonomic identity per se. For biological accumulations, however, taxonomic composition reflects the preferences of the individual agents of accumulation. The probability of preservation of taxa in fluvial accumulations is probably mainly a function of body size, as reflected in the sizes of isolated skeletal elements. Thus, in this Siwalik system, bone assemblages that experienced fluvial transport are better representations of original community composition than bone assemblages created by biological agents or passive accumulation.
Shape, Drag, and Power in Ammonoid Swimming
Authors: Jacobs David K. 
Published: July 2016

This study assesses swimming potential in a variety of ammonoid shell shapes on the basis of coefficients of drag (Cd) and the power needed to maintain a constant velocity. Reynolds numbers (Re) relevant to swimming ammonoids, and lower than those previously studied, were examined. Power consumption was scaled to a range of sizes and swimming velocities. Estimates of power available derived from studies of oxygen consumption in modern cephalopods and fish were used to calculate maximum sustainable swimming velocities (MSV).Laterally compressed, small thickness ratio (t. r.) ammonoids, previously assumed to be the most efficient swimmers, do not experience the lowest drag or power consumption at all sizes and velocities. At low values of size and velocity associated with Reynolds numbers below 104, less compressed forms have smaller drag coefficients and reduced power requirements. At hatching a roughly spherical shell shape would have minimized drag in ammonoids; with increasing size, hydrodynamic optima shift toward compressed morphologies.The high energetic cost of ammonoid locomotion may have limited dispersal and excluded ammonoids from high current velocity environments.
Congruence between parsimony and stratigraphy: comparisons of three indices
Authors: Hitchin Rebecca , Benton Michael J. 
Published: July 2016

Use of quantitative statistical tests can show that there is generally good congruence between estimated cladistic hypotheses of relationship and observed stratigraphy. A data set of 376 cladograms of fishes, continental tetrapods, and echinoderms was tested using three metrics, Spearman Rank Correlation (SRC), Relative Completeness Index (RCI), and Stratigraphic Consistency Index (SCI), to explore the relationships between the indices and differences in results among the three groups of organisms.There is a strong relationship between SCI and SRC, since both tests measure the same aspect of the fossil record. There is no relationship between RCI and either SCI or SRC. There is a highly significant relationship, as expected, between SRC coefficients and the number of taxa in a cladogram, but no such relationship for RCI or SCI (except in fishes). There is no significant relationship between any of the indices and either the number of internal nodes or tree balance.Echinoderms show the best stratigraphic consistency of nodes, while continental tetrapods have the best matching of stratigraphic age and cladistic node order. Fishes have the worst match of age and clade ranks, but they do have the most complete fossil record as measured by the RCI. They are followed by echinoderms, and then continental tetrapods, which have the least complete record. This seems to show that life in an aquatic environment leads, in general, to a more complete fossil record.
Plankton ecology and the Proterozoic-Phanerozoic transition
Authors: Butterfield Nicholas J. 
Published: July 2016

Most modern marine ecology is ultimately based on unicellular phytoplankton, yet most large animals are unable to graze directly on even relatively large net phytoplankton; the repackaging effected by herbivorous mesozooplankton thus represents a key link in marine metazoan food chains. Despite the deep taphonomic biases affecting plankton fossilization, there is a clear record of phytoplankton from at least 1800 m.y ago. Proterozoic plankton are represented by small-to medium-sized sphaeromorphic acritarchs and probably do not include many/most of the unusually large acritarchs that characterize the Neoproterozoic. The first significant shift in phytoplankton diversity was therefore the rapid radiation of small acanthomorphic acritarchs in the Early Cambrian. The coincidence of phytoplankton diversification with the Cambrian radiation of large animals points compellingly to an ecological linkage between the two, particularly in light of recently discovered filter-feeding mesozooplankton in the Early Cambrian. The introduction of planktic filter feeders would have established the second tier of the Eltonian pyramid, potentially setting off the “self-propagating mutual feedback system of diversification” now recognized as the Cambrian explosion (Stanley 1973, 1976).By consuming significant percentages of net phytoplankton and suspending it as animal biomass and non-aggregating fecal pellets, mesozooplankton cause a netreductionin export production; a general introduction of zooplankton would therefore have reduced carbon burial and moderated the bloom and bust cycle that must have characterized Proterozoic populations of net phytoplankton. The effect of added trophic levels in Early Cambrian ecosystems can be viewed as a serial application of the trophic cascade process observed in modern lakes, whereby the introduction of higher trophic levels determines the accumulation of plant biomass at the base of the system. As such, the major biogeochemical perturbations that mark the onset of the Phanerozoic might be considered a consequence, rather than a cause, of the Cambrian explosion; reduced C export due to zooplankton expansion explains the otherwise anomalous drop in δ13C at the base of the Tommotian.Cambrian acanthomorphic acritarchs likely derived from planktic leiosphaerids exposed to mesozooplanktic grazing pressure, the ornamentation effectively increasing vesicle size without compromising buoyancy or surface-area:volume ratios. Alternatively, they may represent an escape into the plankton through a miniaturization of the much larger Neoproterozoic acanthomorphs. An invasion of small benthic herbivores into the water column to exploit the phytoplankton accounts for the origin of the mesozooplankton and may have been the key innovation in the Cambrian explosion.
Community paleoecology as an epiphenomenal science
Authors: Hoffman Antoni 
Published: July 2016

The most important topics discussed thus far by community paleoecologists are: community approach to paleoenvironmental reconstruction, community development in evolutionary time, and community constraints upon species evolution. The first step in community-paleoecological analysis is to reconstruct the paleocommunity or paleoecosystem. However there are severe methodological limitations to any inference drawn from the composition and structure of a fossil assemblage. These result from various taphonomic biases. These constraints upon reliability of a community-paleoecological analysis are the least severe in the case of Cenozoic (and possibly Cretaceous) tropical to subtropical, molluskdominated, subtidal, benthic communities.The basic assumption of community paleoecology is that communities or biocoenoses represent a distinct, real level of biotic organization achieved through ecological integration of and coevolution among the species. This assumption seems to be invalid for two reasons. (1) The actual degree of community integration is in general insufficient to induce any driving forces for a structural development as predicted by the system theory. (2) The concept of biological reality and distinctness of the community level of biotic organization implies assignment of a significant role to group selection. The assumption that ecological communities achieve with time an equilibrium state representing an optimum habitat partitioning among the component species is invalid, at least as a generalization. This idea is largely falsified and refuted by a variety of ecological studies. Ecological communities are then merely an epiphenomenon of the overlap in distributional patterns of various organisms. There is no intrinsic, biotic mechanism inducing community dynamics in either ecological, or evolutionary time.In spite of this conclusion, the so-called “community approach” under favorable taphonomic conditions is among the most reliable methods of paleoenvironmental reconstruction, and the data on so-called “community evolution” are relevant to the problem of a relationship between actually realized niche patterns and their environmental framework. The latter problem can also be approached through analysis of longevity-frequency-distributions of chronospecies found living together in various habitats. A preliminary investigation may indicate that the precondition to optimization of niche dimensions through coevolution among ecologically related species was met in subtidal benthic habitats but not in pelagic ones. To account for a niche subdivision among planktonic organisms, one has therefore to invoke a stochastic pattern of speciation rather than coevolutionary mechanisms.
Phenetic discrimination of biometric simpletons: paleobiological implications of morphospecies in the lingulide brachiopodGlottidia
Authors: Kowalewski Michał , Dyreson Eric , Marcot Jonathan D. , Vargas José A. , Flessa Karl W. , Hallman Diana P. 
Published: July 2016

The extreme morphological simplicity of lingulide brachiopod shells makes them particularly useful for investigating the species-level taxonomic resolution of the fossil record as well as the relationships between taxonomy, morphological complexity, and evolutionary rates. Lingulides have undergone little change in shell morphology and have had low taxonomic diversity since the Paleozoic. Is this pattern an evolutionary phenomenon or an artifact of the shell's simplicity? Multivariate methods were used to establish morphogroups among seven populations of four extant species ofGlottidia.Six characters (three shell dimensions and three internal septa) were measured for 162 specimens from field and museum collections. All populations follow similar allometric trajectories: internal septa display positive allometry and shell dimensions display negative allometry. The allometric pattern may reflect D'Arcy Thompson's Principle of Similitude. Principal component analysis does not reveal any distinct clusters inGlottidiamorphospace but suggests that some differences independent from ontogeny exist among the populations. Size-free canonical variate analysis indicates the presence of five size-invariant groups that are statistically distinct. Bootstrap-corrected error rates indicate that four specimens are enough to classify a sample correctly atα= 0.05 and eight specimens atα= 0.01. The groups are consistent with neontological classification with the exception of two populations ofG. pyramidataidentified by discriminant analysis as two distinct groups. The size-free morphogroups reflect geographic separation rather than ontogenetic or substrate differences among the populations.Despite the morphological simplicity of the shell, size-free multivariate analysis ofGlottidiadelineates groups that offer taxonomic resolution comparable with the neontological classification. The method offers a promising tool for identifying natural morphogroups on the basis of few morphological characters. Moreover, the agreement between neontological taxonomy and the morphogroups suggests that the size-free approach can be applicable for evaluating the reality of the low diversity and turnover rates observed in the fossil record of lingulide brachiopods (= Family Lingulidae). Assuming that the neontological species ofGlottidiaare biologically meaningful, this study shows that morphological simplicity of lingulides does not necessarily result in taxonomic underresolution. Our analysis, as well as several previous case studies, suggests that taxonomic diversity and turnover rates do not have to be dependent on the morphological complexity of preservable parts. In many cases, when rigorous quantitative methods are employed, the differences in the rates of morphological evolution may be a real evolutionary phenomenon and not artifacts of morphological complexity.