bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Rhuddanian (Silurian: Lower Llandovery) echinoderm fauna from Haverfordwest, Southwest Wales
Authors: Donovan Stephen K. , Veltkamp Cornelis J. 
Published: January 2018

Llandovery (Lower Silurian) echinoderm faunas are uncommon, an observation which has important implications for our understanding of the patterns of evolution and extinction over the Ordovician/Silurian boundary interval. For example, only two crinoid faunas of Rhuddanian or Rhuddanian+Aeronian age have so far been described, both from North America (Cataract Group, Ontario; Brassfield Formation, Ohio). A third echinoderm fauna of Rhuddanian age is now recognized from the Gasworks Mudstones (=upper Haverford Mudstone Formation) and, less certainly, the Gasworks Sandstone Formation of Haverfordwest, Dyfed, southwest Wales. Recent fieldwork has failed to relocate the precise horizon that produced this fauna and the taxa discussed herein are all based on specimens in the Turnbull Collection of the Sedgwick Museum, Cambridge. There is no published analysis of this fauna, but Ramsbottom, in his Ph.D. thesis, identified Pisocrinus sp., Macrostylocrinus sp. and Dimerocrinites sp. from this horizon.A disarticulated thecal plate has been identified as the rhombiferan Homocystites? sp., confirming that the cheirocrinids survived the end Ordovician extinction. This is only the second British Llandovery cystoid. All other specimens are crinoids. Crowns of calceocrinid disparids are assigned to two species of Calceocrinus (=“Pisocrinus sp.” of Ramsbottom). A dendrocrinid cladid is interpreted as a smmoth-cupped Dendrocrinus? A unique internal mould is a monobathrid, possibly Macrostylocrinus. Distinctive petaloid columnals of Floricolumnus (col.) sp. cf. F. girvanensis Donovan and Clark, possibly derived from a rhodocrinitid diplobathrid, are congeneric with ossicles from the Newlands Formation of southwest Scotland (latest Rhuddanian-earliest Aeronian) and the Brassfield Formation of Ohio (‘Bead Bed’). A new species of rhodocrinitid diplobathrid (=“Dimerocrinites sp.” of Ramsbottom) has low infrabasals just apparent in lateral view; a moderately bowl-shaped dorsal cup; prominent ray ridges; 2, 3 or 5 plates, respectively, in the first three tiers of interprimibrachials; and uniserial arms that branch isotomously once and heterotomously thereafter. Two further crinoid species are indeterminate. At the familial level, this fauna shows strong similarities with coeval, but more diverse, crinoid assemblages from North America.
Trilobite vision: a comparison of schizochroal and holochroal eyes with the compound eyes of modern arthropods
Authors: Fordyce David. , Cronin Thomas W. 
Published: January 2018

The compound eyes of trilobites provide the best examples of fossilized sensory organs for which the function in life can be worked out today, because the optical array of their corneal lenses preserves the geometry with which the eye originally sampled the visual world. An analysis of trilobite vision is strengthened by the use of new mathematical approaches to compound eye design. In particular, the product of the facet diameter (D) and the interommatidial angle (Δϕ) gives the value of the eye parameter, DΔϕ, which is a reliable indicator of the photic conditions in which the eye was used. In modern arthropods, DΔϕ values range from 0.3 for animals active in bright sunlight to 20 or more for nocturnal or deep-sea animals.Three types of compound eyes existed in trilobites: schizochroal, holochroal, and abathochroal. We examined the schizochroal and holochroal types. Schizochroal eyes were studied in the phacopid species Phacops rana crassituberculata and Phacops rana milleri. We measured the diameter of every corneal lens, and estimated its optical axis by taking the normal to the plane of the lens's diameter. In both species, each eye covered almost exactly 180° of visual space in azimuth with no binocular overlap, from directly anterior to directly posterior. Vertically, the visual field extended from the horizon to about 40° in elevation. Facet diameters and interommatidial angles were large, giving eye parameter values ranging from 10 to > 150. These are much greater than in any living arthropod, implying that modern compound eye theory does not apply to schizochroal eyes. We believe that each ommatidium of the schizochroal eye served as a miniature lens eye. If so, phacopid vision must have been unique, with multiply overlapping visual fields. Such a design would have required considerable central processing, but could have provided exceptional opportunities for spatial, spectral, and polarizational analysis.We examined holochroal compound eyes in Asaphus cornutus and Isotelus “gigas”. Here, visual field coverage was greater than in the schizochroal eye type, with a small amount of frontal binocular overlap. Holochroal eyes contain far more ommatidia than do schizochroal types, reducing both facet diameter (D) and interommatidial angle (Δϕ). Thus, DΔϕ values in these species fall into the same range as in modern compound eyes. This implies that function of the holochroal eye was similar to that of modern crustaceans and insects.This material is based on research supported by the National Science Foundation under Grants No. BNS-8518769 and BNS-8917183.
Phylogenetic history of major trilobite clades in relation to paleoenvironment
Authors: Fortey Richard A. , Owen Robert M. 
Published: January 2018

Because trilobites occupied a wide a range of Paleozoic marine habitats they are a good group to examine hypotheses concerning the sites in which new major clades first appear, and their subsequent history of diversification and decline. There are several problems in this endeavour. The first concerns classification. Until a complete phylogenetic classification is available, there is no objective way to assess the equivalence or otherwise of groups which have been claimed as orders. For example, Odontopleurida and Lichida are treated as separate orders in some classifications, but are considered as a single major clade - presumably of ordinal status - in others. Some of the most commonly accepted groups (Olenellida, Ptychopariida) are paraphyletic. The second problem is taphonomic. The first appearance of a major group often coincides with a major extrinsic change, such as a regressive-transgressive couplet. Does the event initiate the novelty, or simply permit it to be preserved? Does such an event “punctuate” the fossil record, such that earlier, ancestral taxa belonging to the same clade go unrecognised?Trilobites are already paleogeographically diversified when they make their first appearance in the Lower Cambrian. Since trilobites constitute a true clade, this implies an earlier phase of vicariance of dispersal which is not recorded in the rocks. In China, Siberia, North America, and North Africa these first occurrences are in rocks of inshore origin: still earlier trilobites may have had thin cuticles which militated against their being preserved in the highest energy environments where “small shelly” fossils occurred. The groups Olenellida, Redlichiida, Corynexochida, Ptychopariina (?Lichida) appear in the early Cambrian. The earliest polymerids with morphology corresponding to deep water, atheloptic, is latest Lower Cambrian (Atops, Australia): there are many such in the mid-Cambrian.Opinions differ on the classification of Agnostida. Our own view relates Agnostina to Eodiscina, and on this view the early representatives of the clade (Lower Cambrian, China) are inshore compared with later agnostid occurrences, which typify outer shelf to slope. Ordovician agnostids are comparatively rare; the youngest agnostids were not confined to deep water sites.There is good evidence of early occurrences of Odontopleurida, Lichida s.s., Illaenina, Proetida and Phacopida in shallow water deposits. Evidence from Asaphida is more equivocal. Colonisation of deeper water habitats from shallow is rapid, although not achieved at the same time in each group. The scenario is of repeated production of deeper water forms from shelf taxa rather than wholesale movement of clades into that environment. After the demise of other groups in the late Devonian, for example, in the youngest Devonian and Carboniferous proetides radiated into deep water habitats. But the last trilobites of all in the Permian were shallow shelf inhabitants.
Mammalian lineages in the Paleogene of Wyoming-Montana: rates of change, species longevities, and modes of speciation
Authors: Gingerich Philip D. , Gunnell Gregg F. 
Published: January 2018

The Clarks Fork Basin in northwestern Wyoming contains a thick stratigraphic section of Paleocene and Eocene fluvial sediments, parts of which are exceptionally complete and very important for quantitative study of mammalian evolution. The 1520-2270 m interval of the early Eocene in the Clarks Fork Basin, representing about 2 m.y. of evolutionary time, has been sampled on a scale of 10 m ≈ 27,000 years.Rates of morphological change can be calculated from measurements of tooth size for successive large samples in this section. These are quantified in terms of proportional change in standard deviation units, with time in generations. Fig. 1 (lower left) shows the distribution of 548 nonzero rates for the dawn horse Hyracotherium grangeri lineage plotted on log-log axes. The distribution has a robust maximum likelihood slope of -0.923 with a bootstrapped confidence interval ranging from -0.798 to -1.041: the observed interval includes -1.00 expected for a stabilizing process (stasis), but excludes -0.50 expected for random change and 0.00 expected for a process like directional selection. Extrapolation indicates H. grangeri changed at an intrinsic rate of 0.23 standard deviations per generation on a time scale of one generation (95% CI ranges from 0.06 to 0.87). This and other examples known to date suggest intrinsic rates for lineages in stasis are indistinguishable from (no lower than) intrinsic rates for artificially selected directional change in laboratory selection experiments. Consequently, significant differences in net change observed over time cannot be explained intrinsically but must be due to extrinsic factors.Species durations can be estimated to the nearest 0.1 m.y. for 46 well sampled lineages (open histogram in Fig. 2, lower right, cross-hatched where overlapping black Poisson distribution with same half-life λ). Median duration is 0.5 m.y., modal duration is 0.3 m.y. Note excess of both short- and long-duration species, indicating durations are neither independent of each other nor an intrinsic property of species. Here again, change and speciation, fast or slow, are probably driven by environmental factors extrinsic to the species themselves.
Some recent advances in the study of deep-sea foraminiferal biology and their palaeoecological significance
Authors: Gooday Andrew J. 
Published: January 2018

During the past two decades, biologists have become increasingly aware of the diversity and abundance of foraminifera in marine benthic ecosystems. These protists are probably the most important eukaryotes present in ocean floor communities. In some areas, particularly central oceanic regions, foraminiferal assemblages are dominated by newly discovered, soft-bodied forms with morphologies quite unlike those of “conventional” foraminifers and with little fossilisation potential. However, despite the presumed loss of these delicate forms from the fossil record, foraminiferal tests are still the only microfossils to occur commonly in ancient deep-sea sediments. Thus, they are a focus of attention for both geologists and biologists. This presentation will concentrate on two main areas of biological research which have palaeontological significance.Foraminiferal microhabitats. Recent research indicates that particular species tend to live infaunally (deep or shallow), epifaunally or suprabenthically. Growth above or below the sediment-water interface has major implications for the stable isotope chemistry of calcareous tests, an important tool in palaeooceanography. Other species inhabit organic detritus composed of phytoplankton material rapidly sedimented from the euphotic zone. This “phytodetritus” arrives suddenly on the ocean floor following the spring bloom and is quickly colonized by foraminiferal species which feed on it, reproduce and rapidly develop large populations. These populations collapse when the food source is exhausted. The direct consumption of phytodetritus (and other organic matter inputs) by benthic foraminifers may be a widespread phenomenon which influences their population dynamics, regional distribution patterns and isotope chemistry.Recolonization. The defaunation of large tracts of ocean floor by turbidity currents or anoxic events must have happened on countless occasions over geological time, particularly along ocean margins and in basinal areas. Evidence from sediment tray experiments suggests that it may take several years for a stable community (including foraminifers) to become reestablished in small areas of defaunated sediment. Large devastated areas may require substantially longer to recover. However, on the Madeira Abyssal Plain, a normal foraminiferal assemblage occurs on the surface of a turbidite deposited several hundred years ago, suggesting that large-scale recolonization may occupy decades rather than centuries. The fossil foraminiferal assemblages present in deep-water flysch sequences are presumably the product of similar recolonization (?successional) events.These and other biological processes often operate on time scales (days, months, years) which usually can not be resolved in the stratigraphic record. This inevitably complicates the application of biological research to palaeontology.
The evolution of bivalves defences: constraints and preadaptations
Authors: Harper Elizabeth 
Published: January 2018

The marked increase in predation pressure at the close of the Palaeozoic must have had a profound effect on the evolution of the bivalves (Vermeij, 1983). In particular the epifaunal bivalves were extremely vulnerable to attack by the major molluscivore groups; fish, asteroids, crustaceans and boring and wedging gastropods.The range of techniques employed by these molluscivores ranges from crushing and prising to boring and the range of effective defensive measures is correspondingly broad. Different methods of attack require different and, perhaps conflicting, defensive strategies. The bivalves undergo a massive radiation at the beginning of the Mesozoic, a time coincident with the increase in predation pressure (with the important exception of the boring gastropods which evolved much later in the Cretaceous). Given the range of methods of attack and the myriad of possible prey responses it is possible to interpret almost any change in life habit or morphology happening at that time as defensive. Temporal coincidence is not sufficient and such interpretations should be supported with experimental data from predation on Recent malacofauna.Nevertheless, a number of bivalve life habits may be interpreted as having evolved in response to predation pressure. Inevitably certain taxa are prevented from evolving particular defence mechanisms by the constraints of their body plans. The aim of this paper is to explore the different evolutionary pathways followed by different clades in terms of their constructional potentialities and constraints.
Patterns of evolution before extinction of Triassic conodonts
Authors: Hirsch Francis 
Published: January 2018

After surviving the notorious Permian-Triassic boundary-events, the conodont-bearing animals underwent a number of crisis at the end of Induan, Olenekian, Ladinian, Early Carnian and during Middle Norian to Rhaetian times, before their final extinction at the end of the Triassic. The causes responsible for speciation, radiation and extinction seem possibly related to global sea-level changes, although the Norian-Rhaetian speciations and final extinction of conodonts may have been controlled by competitional pressure at the trophic and reproductive level, possibly by newly appeared taxa, e.g. bonefishes.Families, defined herein by their multielement-apparatus, are three in number (4 genera, 1 being new) in Induan, two (8 genera, 6 new) in Olenekian, one (2 subfamilies, 5 genera, 3 new) in Anisian, Ladinian and Early Carnian before the Carnian crisis, and one (1 subfamily, 2 genera, 1 new genus) in Late Carnian, Norian and Early Rhaetian, until extinction of the last conodont taxon at the end of the Rhaetian.Palaeogeographic distribution of Induan Anchignathodus, Induan - Olenekian Ellisonia and Neospathodus, Induan - Early Rhaetian Neogondolella and Olenekian Plativillosus are boreal to equatorial. Olenekian Furnishius, Parachirognathus, Hadrodontina and Pachycladina are found in cratonic cordilleran and Werfen facies. Latest Olenekian, respectively Anisian to Early Carnian Gladi- and Paragondolella define low-latitude mesopelagic Tethys. Ladinian Sephardiella extends from shallow Tethys to Boreal realms, whereas Neogondolella and Pseudofurnishius dwelled respectively in restricted Anisian to Early Ladinian Germanic and semi-open Ladinian Sephardic provinces. The specialization of post-Induan taxa into environmental niches became first reduced from the generic to specific level and disappeared entirely in Late Norian and Rhaetian. Latest Carnian - Latest Rhaetian Epigondolella species extended from low (Tethyan) to high (Boreal) latitudes, in pelagic and cratonic facies. Norian species of Paragondolella had a pan-thallassic, including Notal, distribution.Triassic P-elements always show similar patterns of evolution of the platform and basal cavity as appearance of denticles on platform -edges, development of a free blade and splitting of basal cavity, causing broadening of platform. These characters are lost or abandoned in highly critical periods. Instead, ancestral morphs with reduced platforms, often without apparatus, or early ontogenetic stages, re-appear, from which evolution restarts. Norian-Rhaetian taxa, however, seem to play that scenario backwards, a process reminding of neoteny or paedomorphism. This process is accompanied by the irreversible reduction in the number of species of Late Rhaetian conodonts.
Ecophenotypic variation and phylogeny within the Erisocrinacea (Crinoidea): linkage of morphology, ecology, & sea - level in the Late Paleozoic
Authors: Holterhoff Peter F. 
Published: January 2018

Cyclothems (fifth - order depositional sequences) are the fundamental stratigraphic motif of the Upper Pennsylvanian and Lower Permian of the North American mid - continent. Through this interval, sequences display an overall second order regression modulated by intermediate frequency sea-level fluctuations. Thus, shelfward incursions of offshore (basinal) facies are more extensive in the lower Upper Pennsylvanian, while merely shoaling facies characterize marine units of many higher sequences.Within basal Upper Pennsylvanian (Missourian) sequences, species of the Erisocrinacea are ubiquitous members of nearshore and offshore crinoid assemblages. However, the species Erisocrinus typus and Delocrinus subhemisphericus display significant ecophenotypic variation between facies: smaller mean and maximum size characterizes offshore/transgressive populations while larger size characterizes nearshore/regressive populations. It is proposed that these are hydrographically - controlled phenotypes: offshore, quiet bottom waters inhibit effective filtration, imposing a metabolic energy threshold beyond which larger morphologies are not viable while nearshore populations are able to assume larger body sizes.Shifting now to the Catacrinidae within the Erisocrinacea, as the frequency of interbasinal drowned shelf conditions waned through the Late Pennsylvanian, new species, inhabiting regressive facies, increased maximum body size and diversity for the family. Thus, lower Virgilian assemblages are highly variable in characteristic size, with smaller, ancestral D. subhemisphericus dominant in offshore facies while robust D. vulgatus, Pyndaxocrinus sp., and Arrectocrinus sp. dominate nearshore facies. Speciation may have involved the stabilization and subsequent diversification of the earlier nearshore phenotype.Through the remainder of the Virgilian and into the Early Permian, near the terminal late Early Permian regression, larger morphologies, represented by D. brownsvillensis, D. vastus, and A. abruptus, dominate midcontinent crinoid assemblages; smaller offshore species had been lost, thus increasing body size for the clade as a whole.Thus, it appears that the same parameters which controlled morphological expression at the fifth - order level (ecophenotypic variation) may also have acted at the second - order level (phylogenetic trend). The interrelationship between sub-cycle and super-cycle sea - level and metabolic viability is paramount to understanding potential morphologies for this clade. However, these factors may not have ultimately influenced clade diversity.
Endemicity analysis of global Cretaceous dinosaurian faunas
Authors: Holtz Thomas R. 
Published: January 2018

It has often been assumed that the intensively studied dinosaur faunal assemblages of western North America and the Gobi Desert of Mongolia and China represent “typical” Late Cretaceous terrestrial vertebrate communities. This assumption has led to a paleoecological scenario in which a global ecological shift occurs from the dominance of high-browsing saurischian (i.e., sauropod) to low-browsing ornithischian (i.e., iguanodontian, marginocephalian, ankylosaurian) herbivore communities. Furthermore, the assumption that the Asiamerican dinosaur faunas are communities “typical” of the Late Cretaceous has forced the conclusion that the sauropod-dominated Argentine population must have been an isolated relict ecosystem of primitive taxa (i.e., titanosaurid sauropods, abelisaurid ceratosaurs). Recent discoveries and reinterpretations of other Late Cretaceous assemblages, however, seriously challenge these assumptions.Paleogeography and paleobiogeography have demonstrated that terrestrial landmasses became progressively fractionated from the Late Jurassic (Kimmeridgian-Tithonian) to the Late Cretaceous (Campanian), owing to continental drift and the development of large epicontinental seas (the Western Interior Seaway, the Turgai Sea, etc.). The Maastrichtian regressions resulted in the reestablishment of land connection between long isolated regions (for example, western and eastern North America). These geographic changes are reflected in changes in the dinosaurian faunas. These assemblages were rather cosmopolitan in the Late Jurassic (Morrison, Tendaguru, and Upper Shaximiao Formations) but became more provincialized throughout the Cretaceous.Cluster analysis of presence/absence data for the theropod, sauropod, and ornithischian clades indicates that previous assumptions for Late Cretaceous dinosaurian paleoecology are largely in error. These analyses instead suggest that sauropod lineages remained a major faunal component in both Laurasia (Europe, Asia) and Gondwana (South America, Africa, India, and Australia). Only the pre-Maastrichtian Senonian deposits of North America were lacking sauropodomorphs. Furthermore, the abelisaurid/titanosaurid fauna of Argentina is, in fact, probably more typical of Late Cretaceous dinosaurian communities. Rather, it is the coelurosaurian/ornithischian communities of Asiamerica (and particularly North America) that are composed primarily of dinosaurs of small geographic distribution. Thus, the Judithian, Edmontonian, and Lancian faunas, rather than being typical of the Late Cretaceous, most likely represent an isolated island-continent terrestrial vertebrate population, perhaps analogous to the extremely isolated vertebrate communities of Tertiary South America. Furthermore, the shift from high-browsing to low-browsing herbivore “dynasties” more likely represents a local event in Senonian North America and does not represent a global paleoecological transformation of Late Cretaceous dinosaur community structure.