bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth patterns and biological information in fossil fish otoliths
Authors: Woydack Andrea , Morales-Nin Beatriz 
Published: July 2006

Teleost otoliths are located in the membranous labyrinth and are mainly composed of aragonite and a small amount of organic matrix. Their rhythmic growth may provide important data about age, growth, maturity, and life-history events.This article presents insights into paleoecological and evolutionary details from a study of the otolith microstructure of Trisopterus kasselensis, Trisopterus sculptus, and Pterothrissus umbonatus (Oligo-Miocene, North Sea Basin). Otoliths of Recent Trisopterus minutus were analyzed using the same methods (light and electron microscopy, thin slides) as a basis for comparison with the fossil sample.Growth structures similar in size and aspect to the seasonal and daily growth increments in living fish indicate both individual age and early life transitions in habitat and life strategy suggesting planktonic larvae and benthic juveniles. The aspect of rhythmic growth patterns is due to lunar periodicity, a common feature in fish otoliths. Moreover, fossil Trisopterus show an phylogenetic increase in otolith—and consequently—somatic growth, indicating a change of life strategy during evolution (Oligocene to Recent).Thus the internal structure of fossil otoliths allows the determination of growth, age composition, and early life history of fossil fish, as well as their direct comparison with living relatives.
Probing the cassiduloid origins of clypeasteroid echinoids using stratigraphically restricted parsimony analysis
Authors: Smith Andrew. B. 
Published: July 2006

Clypeasteroid echinoids are a familiar and easily defined clade with a cryptic origin. They first appear in the late Paleocene and are believed to have arisen from cassiduloid ancestry, but identifying sister-group relationships more precisely has proved difficult. Two factors are responsible for this problem, the extreme morphological conservatism of cassiduloids, which has given rise to high levels of character exhaustion, and the origin of crown-group clypeasteroids through paedomorphosis. Previous analyses, based on extant representatives alone or including all Mesozoic to Recent genera, have proved unsatisfactory.Here a parsimony analysis is undertaken using a restricted set of all stem-group clypeasteroids and cassiduloid taxa that existed immediately prior to the appearance of crown-group clypeasteroids. Inclusion ofTogocyamus, the fossil taxon lying closest to the origin of crown-group clypeasteroids, is phylogenetically uninformative because that taxon is highly paedomorphic and has only generalized juvenile characteristics. However, earlier stem-group plesions provide critical data that identify Apatopygidae as extant sister group to the Clypeasteroida. Stratigraphically restricted analyses cannot eradicate the problems that arise from character exhaustion, but can minimize these with respect to specific phylogenetic questions.
Uncorrelated change produces the apparent dependence of evolutionary rate on interval
Authors: Sheets H. David , Mitchell Charles E. 
Published: July 2006

An intriguing phenomenon in the study of evolutionary rates of morphological change measured from fossil lineages has been the dependence of these rates on the inverse of the measurement interval. This effect has been reported across wide ranges of species as well as within single lineages, and has been interpreted as representing a smooth extension of evolutionary rate from generational timescales to paleontological timescales, suggesting that macroevolution may be simply microevolution extended over longer intervals. There has been some debate about whether this inverse dependence is a real feature of evolutionary change, or a mathematical or psychological artifact associated with the interpretation of data.Our analysis indicates that the strong inverse dependence of rate on interval is an artifact produced by the phenomenon of spurious self-correlation. Spurious self-correlation can appear in any calculation when a ratio is plotted against its denominator, as is done in plotting rate versus interval, and when these two quantities are not well correlated with one another. We demonstrate that the effect of spurious self-correlation appears in seven published data sets of evolutionary rate that range from taxonomically broad compendia to studies of single families. The effect obscures the underlying information about the dependence of evolutionary change on interval that is present in the data sets. In five of the seven data sets examined there is no significant correlation between the extent of evolutionary change and elapsed time. Where such a correlation does exist, the inverse dependence of rate on interval length is weakened. We describe the role played by taxonomic, dynamic, and character inhomogeneity in producing the lack of correlation of change with interval in each of these data sets. This lack of correlation of change with interval, and the accompanying inverse correlation of rate with interval, most likely arises from discontinuous modes of evolutionary change in which a distinct long-term dynamic dominates net change over geological time spans. It is poorly explained by the extrapolationary microevolutionary models that have been said to account for this phenomenon.
The description and classification of evolutionary mode: a computational approach
Authors: Roopnarine Peter D. 
Published: July 2006

The incorporation of the random walk model into stratophenetic analysis marked a turning point by presenting a potential null model for microevolutionary patterns. Random walks are derived from a family of statistical fractals, and their statistics can be reconstructed using appropriate techniques. This paper lays the foundation for the explicit and uniform description of evolutionary mode in stratophenetic series using random walk null models and the information contained within incompletely preserved time series.The method relies upon the iterative analysis of subseries of an original stratophenetic series by measuring the presence of deviations from statistical randomness as the lineage evolves. This measure, and its probability of significance (evaluated using a randomization test), forms the dimensions of a descriptive space for microevolutionary modes. Each stratophenetic series can then be viewed as a journey through this space. Computer simulation of various evolutionary modes demonstrates that different modes, for example stasis and gradualism, have differing trajectories and occupy different regions of the microevolutionary space. The method is applied to two published foraminiferal stratophenetic series, the Mio-PlioceneGloborotalia plesiotumida-tumidapunctuated transition and an anagenetic trend in the Late CretaceousContusotruncana fornicata-contusalineage. An anagenetic trend is strongly supported in the latter example, whereas transformation of theGloborotaliaspecies seems to result from the fluctuating effectiveness of constraining processes.
Evaluating hypotheses of instar-grouping in arthropods: a maximum likelihood approach
Authors: Hunt Gene , Chapman Ralph E. 
Published: July 2006

The ontogeny of arthropod exoskeletons is punctuated by short periods of growth following each molt, separated by longer stages of unchanging morphology called instars. The recognition of instar clusters in size distributions has been important in understanding the growth and evolution of fossil arthropods. Generally, these clusters have been identified by inspection, but this approach has been criticized for its subjectivity. In this paper, we describe a statistical framework for evaluating hypotheses of clustering based on maximum likelihood analysis of mixture models. The approach assumes that individuals are normally distributed within instars; thus an arthropod size distribution can be considered a mixture of normal distributions. This methodology provides an objective framework to compare various plausible hypotheses of grouping, including the possibility that there is no significant grouping at all.We apply this method to evaluate clustering in two trilobite species,Ampyxina bellatulaandPiochaspis sellata.Both of these data sets show statistically significant evidence of clustering, a phenomenon rarely documented for holaspid-stage trilobites. After consideration of alternative causes of clustering, we argue that the observed groupings are best explained as instar groups. In these two species, growth increments between molts were similar throughout the observed portion of ontogeny, although subtle yet significant variation can be seen within the ontogeny ofAmpyxina bellatula.
Floral response to rapid warming in the earliest Eocene and implications for concurrent faunal change
Authors: Wing Scott L. , Harrington Guy J. 
Published: July 2006

During the first 10–20 Kyr of the Eocene temperatures warmed by 4–8°C in middle and high latitudes, then cooled again over the succeeding ∼200 Kyr. Major changes in the composition of marine and terrestrial faunas, including one of the largest mammalian turnover events of the Cenozoic, occurred during this temperature excursion. To better understand the effects of rapid climatic change on continental biotas, we studied 60 fossil pollen samples collected from 900 m of section spanning approximately three million years of the late Paleocene and early Eocene; the samples come from the Fort Union Formation and Willwood Formation in the Bighorn Basin of northwestern Wyoming, paleolatitude approximately 47°N. There are 40 samples from the 500 m of rock deposited during the one million year interval centered on the Paleocene/Eocene boundary, although pollen was not preserved well in rocks representing the short warm interval at the base of the Eocene.Overall, the palynoflora shows moderate change in composition and diversity. Two pollen taxa clearly expanded their ranges to include North America in the first 400 Kyr of the Eocene,Platycarya(Juglandaceae), andIntratriporopollenites instructus(cf.Tilia), but they account for less than 5% of pollen grains in the early Eocene. There are no last appearances of common taxa associated with the Paleocene/Eocene boundary. The most noticeable palynological changes are the decrease in abundance ofCaryapollenitesspp. andPolyatriopollenites vermontensis(Juglandaceae), and the increase in abundance of Taxodiaceae (bald cypress family), Ulmaceae (elm family), and Betulaceae (birch family), particularlyAlnipollenitesspp. (alder). There are 22% more species in the Eocene samples than in the Paleocene samples; mean richness of Eocene samples is 17% higher than the mean of Paleocene samples. The mean evenness of Eocene samples is higher than that of Paleocene samples, but the difference is not significant.The modest level of floral change during the late Paleocene and early Eocene contrasts with the major taxonomic turnover and ecological rearrangement of North American mammalian faunas observed at the same time. Faunal change probably resulted from intercontinental range expansion across Arctic land bridges that became habitable as a result of high-latitude warming, so it is surprising that climatically sensitive plants did not also experience a major episode of interchange. The absence of fossil plants from the temperature excursion interval itself could prevent us from recognizing a transient shift in floral composition, but it is clear that the flora did not undergo a major and permanent restructuring like that seen in the mammals. The contrast between the moderate floral response to warming and the strong faunal response is consistent with the idea that interactions between immigrant and native taxa, rather than climate directly, were the primary cause of terrestrial biotic change across the Paleocene/Eocene boundary.
Taxon distributions and the tetrapod track record
Authors: Carrano Matthew T. , Wilson Jeffrey A. 
Published: July 2006

Vertebrate tracks are a unique, abundant source of fossil data that supplements the skeletal record in many ways. However, the utility of ichnofossil data depends on how specifically the authors of tracks can be identified. Despite this fact, there is little consensus about how to identify potential trackmakers, and existing methods differ in their bases, assumptions, and corresponding implications.In this paper we support the proposal that trackmakers should be identified primarily by skeletal structures that are both preserved in the ichnofossils and synapomorphies of some body-fossil clade. This synapomorphy-based technique enables certain taxa to be positively identified as candidate trackmakers and others to be excluded from consideration. In addition, the diagnostic level of the synapomorphy (i.e., to a higher or lower level) corresponds to that of the trackmaker. Additional features, such as body size and provenance, can be used in association with synapomorphies as additional differentiae of trackmaker identity.Trackway analyses are dependent on the level of trackmaker diagnosis, but not all analyses require the same diagnostic specificity. Palichnostratigraphic correlations to the stage level are shown to require at least a genus-level identification of a trackmaker, whereas studies of vertebrate distributions (i.e., origins, extinctions, ranges) accommodate much coarser designations. Anachronistic occurrences of trace and body fossils result in range extensions for either the skeletal taxon or the feature in question. For example, the temporal distribution of theropods can be extended on the basis of the footprint record, resulting in an earlier estimated divergence time for Dinosauria.
Biodiversity in the Phanerozoic: a reinterpretation
Authors: Peters Shanan E. , Foote Michael 
Published: July 2006

Many features of global diversity compilations have proven robust to continued sampling and taxonomic revision. Inherent biases in the stratigraphic record may nevertheless substantially affect estimates of global taxonomic diversity. Here we focus on short-term (epoch-level) changes in apparent diversity. We use a simple estimate of the amount of marine sedimentary rock available for sampling: the number of formations in the stratigraphic Lexicon of the United States Geological Survey. We find this to be positively correlated with two independent estimates of rock availability: global outcrop area derived from the Paleogeographic Atlas Project (University of Chicago) database, and percent continental flooding. Epoch-to-epoch changes in the number of formations are positively correlated with changes in sampled Phanerozoic marine diversity at the genus level. We agree with previous workers in finding evidence of a diversity-area effect that is substantially weaker than the effect of the amount of preserved sedimentary rock. Once the mutual correlation among change in formation numbers, in diversity, and in area flooded is taken into consideration, there is relatively little residual correlation between change in diversity and in the extent of continental flooding. These results suggest that much of the observed short-term variation in marine diversity may be an artifact of variation in the amount of rock available for study. Preliminary results suggest the same possibility for terrestrial data.Like the comparison between change in number of formations and change in sampled diversity, which addresses short-term variation in apparent diversity, the comparison between absolute values of these quantities, which relates to longer-term patterns, also shows a positive correlation. Moreover, there is no clear temporal trend in the residuals of the regression of sampled diversity on number of formations. This raises the possibility that taxonomic diversity may not have increased substantially since the early Paleozoic. Because of limitations in our data, however, this question must remain open.
Community structure of Quaternary coral reefs compared with Recent life and death assemblages
Authors: Edinger Evan N. , Pandolfi John M. , Kelley Russell A. 
Published: July 2006

This paper assesses the reliability with which fossil reefs record the diversity and community structure of adjacent Recent reefs. The diversity and taxonomic composition of Holocene raised fossil reefs was compared with those of modern reef coral life and death assemblages in adjacent moderate and low-energy shallow reef habitats of Madang Lagoon, Papua New Guinea. Species richness per sample area and Shannon-Wiener diversity (H′) were highest in the fossil reefs, intermediate in the life assemblages, and lowest in the death assemblages. The taxonomic composition of the fossil reefs was most similar to the combination of the life and death assemblages from the modern reefs adjacent to the two fossil reefs. Depth zonation was recorded accurately in the fossil reefs. The Madang fossil reefs represent time-averaged composites of the combined life and death assemblages as they existed at the time the reef was uplifted.Because fossil reefs include overlapping cohorts from the life and death assemblages, lagoonal facies of fossil reefs are dominated by the dominant sediment-producing taxa, which are not necessarily the most abundant in the life assemblage. Rare or slow-growing taxa accumulate more slowly than the encasing sediments and are underrepresented in fossil reef lagoons. Time-averaging dilutes the contribution of rare taxa, rather than concentrating their contribution. Consequently, fidelity indices developed for mollusks in sediments yield low values in coral reef death and fossil assemblages. Branching corals dominate lagoonal facies of fossil reefs because they are abundant, they grow and produce sediment rapidly, and most of the sediment they produce is not exported.Fossil reefs distinguished kilometer-scale variations in community structure more clearly than did the modern life assemblages. This difference implies that fossil reefs may provide a better long-term record of community structure than modern reefs. This difference also suggests that modern kilometer-scale variation in coral reef community structure may have been reduced by anthropogenic degradation, even in the relatively unimpacted reefs of Madang Lagoon. Holocene and Pleistocene fossil reefs provide a time-integrated historical record of community composition and may be used as long-term benchmarks for comparison with modern, degraded, nearshore reefs. Comparisons between fossil reefs and degraded modern reefs display gross changes in community structure more effectively than they demonstrate local extinction of rare taxa.
Detecting changes in morphospace occupation patterns in the fossil record: characterization and analysis of measures of disparity
Authors: Ciampaglio Charles N. , Kemp Matthieu , McShea Daniel W. 
Published: July 2006

Recently, there has been much interest in detecting and measuring patterns of change in disparity. Although most studies have used one or two measures of disparity to quantify and characterize the occupation of morphospace, multiple measures may be necessary to fully detect changes in patterns of morphospace occupation. Also, the ability to detect morphological trends and occupation patterns within morphospace depends on using the appropriate measure(s) of disparity. In this study, seven measures were used to determine and characterize sensitivity to sample size of the data, number of morphological characters, percentage of missing data, and changes in morphospace occupation pattern. These consist of five distance measures—sum of univariate variances, total range, mean distance, principal coordinate analysis volume, average pairwise dissimilarity—and two non-distance measures—participation ratio and number of unique pairwise character combinations. Evaluation of each measure with respect to sensitivity to sample size, number of morphological characters, and percentage of missing data was accomplished by using both simulated and Ordovician crinoid data. For simulated data, each measure of disparity was evaluated for its response to changes of morphospace occupation pattern, and with respect to simulated random and nonrandom extinction events. Changes in disparity were also measured within the Crinoidea across the Permian extinction event.Although all measures vary in sensitivity with respect to species sample size, number of morphological characters, and percentage of missing data, the non-distance measures overall produce the lowest estimates of variance (in bootstrap analyses). The non-distance measures appear to be relatively insensitive to changes in morphospace occupation pattern. All measures, except average pairwise dissimilarity, detect changes in occupation pattern in simulated nonrandom extinction events, but all measures, except number of unique pairwise character combinations and principal coordinate analysis volume, are relatively insensitive to changes in pattern in simulated random extinction events. The distance measures report similar changes in disparity over the Permian extinction event, whereas the non-distance measures differ. This study suggests that each measure of disparity is designed for different purposes, and that by using a combination of techniques a clearer picture of disparity should emerge.
Substrate affinities of higher taxa and the Ordovician Radiation
Authors: Miller Arnold I. , Connolly Sean R. 
Published: July 2006

The Ordovician Radiation exhibited a global transition in dominance from the Cambrian evolutionary fauna (e.g., trilobites), to the Paleozoic and Modern faunas (e.g., articulate brachiopods and bivalve molluscs). Although its causes have yet to be determined definitively, the transition coincided with increased global tectonism. Erosion of source areas uplifted during orogenic activity increased the siliciclastic richness of marine substrates in many venues, and it has been hypothesized previously that higher taxa with affinities for siliciclastics diversified in association with these environmental changes, whereas higher taxa not exhibiting such affinities either failed to radiate or declined in diversity. Here, we provide an initial test of this substrate affinity hypothesis by evaluating the Ordovician affinities of trilobites and articulate brachiopods.Our analyses—at the class level for both trilobites and articulate brachiopods, and at the order level for orthid and strophomenid brachiopods—were based on the affinities of constituent genera for siliciclastic, carbonate, and mixed siliciclastic/carbonate settings. Individual genus affinities are calculated with a database of genus occurrences encompassing nine Ordovician paleocontinents. Using these values, we developed a standardized relative affinity (SRA) metric to compare the propensities of higher taxa, and to assess changes in relative affinities of individual higher taxa from series to series.A simple comparison of trilobites and articulate brachiopods for the Ordovician in aggregate does not appear to support the substrate affinity hypothesis: articulate brachiopods, which contributed increasingly to overall diversity through the period, exhibit an overall affinity for carbonates and an aversion to siliciclastics. However, a rather different view emerges when we consider the affinity trajectories of higher taxa through the period: articulate brachiopods exhibit a growing affinity for siliciclastics and a declining affinity for carbonates, whereas the opposite is the case among trilobites. Among constituent articulate brachiopod orders, the affinity trajectories of orthids and strophomenids mirror that of the class. Thus, the increasing dominance of articulate brachiopods in the Middle and Late Ordovician may have been linked to the affinity for siliciclastics of a diversifying subset of the group, but further investigation will be required to verify this claim.