bluuebunny/crossref_metadata_2025_split huggingface dataset:
Paleobiogeographic and paleogeographic significance of Permian brachiopod faunas of the Bilk Creek Limestone, Nevada, and the McCloud Limestone, California
Authors: Hanger Rex Alan 
Published: January 2018

The Bilk Creek Limestone of the Black Rock Terrane in northwestern Nevada and the McCloud Limestone of the Eastern Klamath Terrane in northern California contain a diverse and abundant Permian brachiopod fauna currently under study. The composite rock record of both limestones spans the Wolfcampian and Leonardian stages of the Permian, during which both terranes were part of a volcanic arc separated from the North American continent by a marginal basin of unknown dimension. Brachiopods of this volcanic arc provide important evidence bearing on current hypotheses of Permian paleobiogeography and paleogeography.The Bilk Creek/ McCloud brachiopods are best characterized as an endemic fauna of a unique province and not as a mixed, “Tethyan” and North American fauna. The central problem of these arc faunas is not how similar they are to faunas of the Tethyan basin but why they are so dissimilar from North American faunas. Overlying rock units in both terranes contain Guadalupian brachiopod faunas that are North American in character. The paleobiogeographic pattern is one of decreasing levels of endemism throughout the Wolfcampian and Leonardian, to ultimate deprovincialization during the Guadalupian. This is not consistent with a pantropic dispersal hypothesis.The temporal pattern is consistent with a paleogeographic hypothesis of initial, long-distance separation of arc and continent with convergence of the arc toward the North American continental margin. The dissimilarity of the arc brachiopod faunas to coeval, same-environment faunas of North America suggests that the marginal basin that separated the two must have been several thousand kilometers wide during the Early Permian, producing the endemic fauna. A Japan-style model, with arc and continent in close proximity is not supported.
Rates of evolution and homoplasy
Authors: Hauser David L. , Boyajian George E. , Shubin N.H. 
Published: January 2018

Homoplasy is present in virtually every known systematic analysis and exists at all levels of the Linnaean hierarchy. Despite the nearly universal presence of homoplasy, the patterns and causal mechanisms of it have only recently been addressed.Sanderson and Donoghue (1989) examined the relationships between homoplasy (as measured by the consistency index) and taxonomic rank, the number of characters, and the number of taxa. Their analysis, which involved 60 data sets from the literature, showed a statistically significant and inverse correlation between the number of taxa and the amount of homoplasy exhibited.In order to expand on Sanderson and Donoghue's important contribution, we attempt to dissect the causal mechanisms of homoplasy. As a working hypothesis, we assume that if the number of character states is limited, homoplasy should be a function of at least three factors: 1) the number of cladogenetic events (which is directly related to the number of taxa), 2) the percentage of characters that undergo change at each node, and 3) the probability of any one character changing at any one node. Because the absolute, or even relative, values of the last two factors are rarely known for a given taxonomic group, we used computer generated data sets in order to quantitatively determine the relative importance of these three factors to patterns of homoplasy. Characters were allowed to “evolve” on a preset tree topology; this process was repeated for a wide variety of values for each of the above factors. The correlation of each factor with the consistency index was then examined. In order to control for results that were unique to a given tree topology, the same data sets were generated onto two very different tree topologies (a extensively bifurcated tree and a Hennigian comb).Our preliminary results indicate that homoplasy is much more sensitive to the percentage of characters that change at a given node then to the number of taxa involved (as determined by the amount of variance explained by a regression line). In addition, the nature of the above procedure allows for the analysis of the dynamic relationship between evolutionary rate and constraint (defined as a limitation in the number of character states possible). These two factors conspire to produce homoplasy. The effect of high rates of evolution on homoplasy is magnified by successively greater constraints on character states; conversely, high rates of evolution in conjunction with low degrees of constraint lead to lesser levels of homoplasy.
The characterization of fossil and modern sporopollenins using 13-C solid state nuclear magnetic resonance
Authors: Hemsley Alan R. , Chaloner William G. , Scott Andrew C. , Barrie Patrick J. , Butler David A. 
Published: January 2018

Recent 13C solid state nuclear magnetic resonance studies have demonstrated differences in the composition of sporopollenins (the inert biomolecule forming spore and pollen walls) from the major groups of extant plants. This substance is also the main constituent of fossil spore walls.We have obtained 13C NMR spectra from three species of Carboniferous lycopod megaspores, and in one case, the associated microspores. Additionally, spores from the Devonian plant Parka decipiens Fleming have been analyzed. The spectra obtained are relatively similar although at present it is unclear how much of this similarity results from diagenesis.The spectra of the fossil spores have been compared to those obtained from extant lycopods and from other plant groups. The fossil lycopod spores share some of the distinctive features of modern lycopod sporopollenin but are, none the less, very different. The spectra of the fossil species also demonstrate the loss of constituents known to form a significant part of the sporopollenin in extant species. Our studies show that some of the chemical characteristics of sporopollenins are retained in fossil spores, allowing the investigation of evolutionary changes of sporopollenin within a group and facilitating the assignment of taxonomically enigmatic fossil species. Further investigation of a range of fossil material, combined with data obtained from pyrolysis, should provide further information on the composition of sporopollenin from different plant groups and on its diagenesis.
The importance of paraphyletic groups in mammalian paleobiology
Authors: Janis Christine 
Published: January 2018

The introduction of cladistic techniques in phylogenetic systematics have revolutionized many concepts in mammalian taxonomy: most notably, many early groups have been relegated to the status of paraphyletic or polyphyletic assemblages (e.g. the “Condylarthra” or “stem ungulates” and the “Proteutheria” insectivorans.). While it is important to recognize truly polyphyletic groups (e.g. the “Amblypoda” or Paleogene “pachyderm” analogs), all non-monophyletic groups are now commonly assigned to a similar “wastebasket” status, rendering all events associated with their evolution as “pseudo-events” on the grounds of taxonomic impurity.I am uncomfortable with this tendency for two reasons. The first is philosophical. Monophyly is a time-dependent system of classification: all taxa were monophyletic at their inception and the more successful (i.e. generative) ones must inevitably pass into paraphyly. Cladistic taxonomy claims to be independent of stratigraphic bias, but seemingly has no problem with using an arbitrary cut-off point in the geological record (the Recent) as a means of imposing taxonomic nomenclature. The second is for practical reasons concerning information contained in many of these paraphyletic taxa that is relevant to issues other than phylogenetic systematics.I examine closely the evolutionary histories of early Paleogene “miacoid” carnivores and late Paleogene “gelocid” artiodactyls. The extinction of miacoid species in the Late Eocene (giving rise to families of larger, apparently more actively hunting carnivores) and the extinction of gelocid species in the Late Oligocene (giving rise to families of larger ruminants apparently better equipped to ingest and process fibrous vegetation) were both coincident with major climatic and environmental changes. The change from non-seasonal to seasonal climates in the Northern hemisphere in the late Eocene may have influenced a change in predator adaptive strategies; likewise, the drying trend and spread of more open habitats in the early Neogene may have influenced ruminant foraging strategies. I submit that while not all paraphylectic groups may be useful in this fashion, at least in the above instances much paleobiological information is lost if these groups are dismissed because of their paraphyletic status: their demise reflects not artificial “pseudoextinction” but rather a real loss of archaic adaptations in a changing world.
Origin of the Late Ordovician Lepidocyclus brachiopod fauna in North America and its biogeographic significance
Authors: Jin Jisuo 
Published: January 2018

Three rhynchonellid brachiopod genera, Hiscobeccus, Lepidocyclus, and Hypsiptycha, are the most diagnostic elements of the Lepidocyclus fauna of North America in Late Ordovician time. These are characterized by relatively large, strongly biconvex to globular shells with coarse imbricating growth lamellae and, internally, with septiform cardinal processes in brachial valves. Among the three genera, Hiscobeccus appears the earliest, now known from rocks of late Trentonian-Edenian age in the Canadian Rocky Mountains and Mackenzie Mountains. Morphologically, Hiscobeccus is distinguished from the other two genera by its open delthyrium in the pedicle valve. Early forms of Hiscobeccus show close morphological similarity to Rhynchotrema in their non-globular biconvex shells covered by strong growth lamellae only in the anterior portions. It has been suggested that Hiscobeccus evolved from the Rhynchotrema wisconsinense stock through increase in shell size, globosity, and strength of growth lamellae. Earliest species of Rhynchotrema has been documented convincingly from rocks of early Trentonian age, and the derivation of Hiscobeccus most likely took place during the mid-Trentonian. Lepidocyclus and Hypsiptycha evolved from either Rhynchotrema or Hiscobeccus by developing a pair of deltidial plates covering the delthyrium.Rhynchotrema and other rhynchonellids that evolved before mid-Trentonian time are common to the North American (Laurentian) and the Siberia-Kazakhstan paleocontinents. In contrast, Hiscobeccus, Lepidocyclus, and Hypsiptycha that evolved after the mid-Trentonian are virtually restricted to Laurentia. Therefore, Rhynchotrema marked the last successful intercontinental migration of rhynchonellids during their Llandeilian-Caradocian cosmopolitanism. The pronounced provincialism of the North American Lepidocyclus fauna may have been caused by a number of factors. Facies control is not likely the explanation because these rhynchonellids occur in nearly all the inland and marginal platform seas of Laurentia and commonly are found together in the same types of rocks. Plate tectonics and sea-level changes are considered major causes. The Ordovician rhynchonellids lived in shallow marine (intertidal-subtidal) environments and were incapable of crossing vast, deep oceanic barriers because of their sedentary mode of life and short-lived motile larval stages. The widening of the ocean between North America and Siberia, coupled with high sea-level stand, may have created a sufficiently wide oceanic barrier to interrupt faunal mixing between the two paleocontinents by late Trentonian time. Moreover, the rise in sea level would have resulted in the disappearance of island faunas, which could have served as stepping stones for intercontinental migration of shallow-water benthic faunas during low sea-level stand.
Late Pennsylvanian and Permian Turrilepadida (Machaeridia) from the western and south-central United States
Authors: Kaasa Maurice E. 
Published: January 2018

The Machaeridia is an enigmatic marine fossil group which has been variously allied with the cirripedians, molluscs, annelids, and echinoderms. Although machaeridians have previously been unreported from rocks younger than earliest Pennsylvanian (late Namurian), members of the machaeridian order Turrilepadida are now found to be locally abundant well into the Permian. New occurrences of turrilepadidan sclerites are reported from the Late Pennsylvanian of Texas and the Early Permian of Texas and Nevada.Turrilepadidan sclerites are common in marine shales of Missourian and Virgilian age in north-central Texas. Well preserved turrilepadidan sclerites have been found in the Wolf Mountain Shale (Missourian) and in the Colony Creek, Finis, and Necessity Shales (Virgilian) of north-central Texas. A few sclerites have a high number of closely spaced rugae and are similar to those of Turrilepas, but the most common types of sclerites have relatively few, widely spaced rugae, and many of these show radial ornament like that found on sclerites assigned to the genus Clarkeolepis. Although most forms would be placed in the family Turrilepadidae, a partial specimen from the Finis Shale appears to be a lepidocoleidid sclerite.Silicified sclerites of Permian age have been found in two marine carbonate units: the upper part of the Bird Spring Formation (late Wolfcampian or early Leonardian) of southern Nevada and in the Cathedral Mountain Formation (Leonardian) of West Texas. Although their details are generally poorly preserved, these sclerites appear to be representative of members of the family Turrilepadidae with a different taxon found at each of the two localities.The paleoecology of turrilepadidans is not well known, but each of these occurrences is from a locality that represented an area with a muddy bottom, a slow rate of deposition, and an unusually diverse fauna. The fauna at each horizon is dominated by a large number of brachiopod and mollusc species, many of which were conspicuously encrusted or bored during life or afterwards. Although a few of the sclerites show postmortem encrustations on their inner or outer surfaces, the overall lack of borings or encrustations suggests that the turrilepadidans were mobile, possibly infaunal organisms.
The flat clam controversy: Where did they come from? Where did they go?
Authors: Kauffman Erle G. , Tomás Villamil , Harries Peter J. , Meyer Christian A. , Sageman Bradley B. 
Published: January 2018

Thin-shelled, weakly articulated, epifaunal byssate to free-living flat clams characterize Devonian-Cretaceous dark, organic-rich shale facies. Convergent evolution on the flat-clam morph occurs among several families of Bivalvia. Flat clams regularly occurred in dense populations, dominating low diversity, inequitable communities for which they were commonly the pioneer species and formed shell islands for the colonization of smaller, firm-substrate dependent invertebrates. The unique flat-clam dominated ecosystem, as well as the widespread environments to which they were adapted, disappeared at the end of the Cretaceous. Although locally, low-oxygen benthic muds exist through the Cenozoic to Recent, they do not support large populations of flat clams, whose ecological niche was never filled after the Cretaceous. Flat clams underwent an exponential increase in size and apparent growth rates through the mid- and Late Cretaceous, reaching over 3 m in diameter (Inoceramidae). Most of this increase in shell size also involved expansion of mantle tissue and probably gills, relative to the size of the visceral mass. This suggests specific adaptations to colonization of oxygen-poor benthic habitats with hydrogensulfide enriched substrates, which broadly characterized Paleozoic and Mesozoic epicontinental seas, during greenhouse intervals. Such conditions were particularly well-developed during Cretaceous Oceanic Anoxic Events, at which time flat clams thrived.Functional morphology, geochemistry, and facies associations suggest that many flat clams were chemosymbiotic and/or had greatly expanded oxygen-absorption surfaces. These adaptations allowed them to be opportunistic in chemically stressed benthic environments; growth rates also seem to be enhanced in these environments, a characteristic of living chemosymbiotic species. Many lines of evidence prove that flat clams lived in these environments and do not represent pseudoplanktic rain. A combination of factors seems to have been responsible for their disappearance near the end of the Cretaceous; i.e., mass extinction, loss of primary habitats, and major radiation among bottom-feeding bivalve predators.
Biostratigraphy and biogeography of Frasnian, Upper Devonian conodonts
Authors: Klapper Gilbert 
Published: January 2018

Analysis of Frasnian conodont sequences in the Montagne Noire, southern France, results in the recognition of a conventional zonation consisting of thirteen zones. Graphic correlation of eight Montagne Noire sections with a total of 11 sections in the Alberta Rockies, the Hay River-Trout River areas of the southern Northwest Territories, Canada, the Midcontinent and New York sequences in the United States, and the Canning Basin, Western Australia divides the Frasnian into 34 composite standard units. Most of these sections are dominated by conodonts of the outer-shelf to basinal Palmatolepis biofacies, but those of Hay River-Trout River are occupied by the quite contrasting inner-shelf Polygnathus biofacies. Correlation of the latter with the Montagne Noire zonation is effected only through graphic correlation. The taxonomy of many of the critical species involved in the correlations is based on shape analysis and multielement taxonomy of Palmatolepis.Prevailing opinion is that the Frasnian was a time of cosmopolitanism as exemplified both by benthic organisms, especially corals and brachiopods, as well as conodonts. This contrasts with the Early and Middle Devonian which was a time of significant endemism in benthic fossils and in conodonts. The high point in conodont endemism according to the zone-by-zone analysis of the Early and Middle Devonian (Klapper and Johnson, 1980) was the early Eifelian when there were about 70% endemic species. Although endemism did not reach this high in the Frasnian, analysis of a limited number of intensively collected and studied sections in the Montagne Noire, U.S. and Canada, Western Australia, and the Russian Platform demonstrates levels of endemism ranging from about 30 to 45% in three composites of two zones each. Endemic species occur in both the Palmatolepis and Polygnathus biofacies. Using the Probabilistic Index of Similarity of Raup and Crick (1979), the null hypothesis of randomness is rejected for some paired comparisons between localities representing different biofacies, as would be expected, but it is also rejected between some localities representing the same biofacies on different continents. Although the explanation of significantly dissimilar faunas can be accepted at 95% confidence levels in only a limited number of instances, there are dissimilarities of somewhat lesser magnitude among various paired comparisons. This seems to indicate that the Frasnian was not a time of conodont cosmopolitanism even within the Palmatolepis biofacies.
The development of Early Paleozoic shell concentrations: evidence from the Cambrian and Ordovician of the Great Basin
Authors: Li Xing , Droser Mary 
Published: January 2018

Shell concentrations have constituted an important and conspicuous part of the stratigraphic record since the Early Cambrian. The paleontological and stratigraphic significance of shell beds is well understood, primarily from Mesozoic and Cenozoic examples. Lower Paleozoic fossil concentrations, however, have not received much attention. The Cambrian and Ordovician evolutionary radiations were two of the most significant events in the history of life and established the Cambrian and Paleozoic faunas respectively. In order to determine the effect of these radiations on the development of fossil accumulations, a systematic study of early Paleozoic shell beds was conducted in the Great Basin areas of California, Nevada, and Utah.In order to minimize taphonomic variations in original chemical and physical conditions, shell beds were compared from strata deposited in similar depositional environments from similar tectonic settings. Preliminary analysis of the shell beds from relatively pure carbonate facies and mixed carbonate and siliciclastic facies shows: 1) that shell concentrations became a significant stratigraphic feature in the later Early Cambrian; 2) the thickness and lateral extent of the shell beds increase from Early Cambrian to Middle Ordovician; 3) the abundance and internal complexity of the shell beds increase from Early Cambrian to Middle Ordovician; and 4) the Cambrian and Early Ordovician shell beds are primarily, if not exclusively, dominated by trilobites whereas the Middle Ordovician shell beds are dominated by brachiopods and ostracodes.These data show a temporal trend in the development of the early Paleozoic shell beds. The nature of the Cambrian and Ordovician shell beds differs qualitatively and quantitatively. There is an increase in physical scale, abundance, and internal complexity through time. The thickness and abundance of the trilobite beds increase through the Cambrian. Interestingly, although trilobites were still diverse and abundant, they did not commonly generate thick trilobite beds after the Late Cambrian. The early Middle Ordovician is a critical time in the development of early Paleozoic shell beds. A variety of monotaxic and polytaxic shell beds, including 6m thick composite beds, first appeared at this time. While the brachiopods and ostracodes generate laterally extensive, commonly monotaxic, shell beds, the gastropods and bryozoans only formed lenticular concentrations.