bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Rates of evolution and fossils in phylogenetic analysis: a computer simulation approach
Authors: Huelsenbeck John P. , Hillis David M.
Published: January 2018

Whereas many studies have examined the performance of various character-data sets in phylogenetic analysis, little work has been done on the effect that various classes of taxa have on phylogenetic reconstruction. In particular, the “fossil versus living taxa” debate has concentrated mainly on the effects of fossils in reconstructing vertebrate and plant relationships. While this work has contributed to the understanding of the role that fossils play in systematics, a computer model clarifies the relationship among the main determinants of the fossil-taxa problem. In addition, simulations of phylogenies over a wide spectrum of evolutionary rates clarify the relative efficiencies of various tree-estimation procedures.

In this study, computer generated phylogenies were used to examine the relationship between the temporal position and completeness of additional taxa in a phylogenetic analysis and the rate of evolution or, equivalently, the temporal scope of the phylogenetic problem. In the simulations, four fossil taxa of varying temporal position and completeness were added to an analysis that included four living taxa. Additional taxa varied in completeness (25%, 50%, 75%, and 100% completeness) and in temporal position (0%, 33%, 66%, and 100% of the distance from the ancestor to the living time plane). Fifty trees were generated each for low, low intermediate, high intermediate, and high rates of evolution or temporal scope. Because additional taxa that are 100% complete and 100% of the distance to the living time plane are equivalent to the addition of living taxa, this study directly compares the effects of addition of living versus fossil taxa in phylogenetic analysis.

The importance of fossil taxa varied depending on their completeness and temporal position and on the rate of evolution under which the phylogeny was generated. In general, high completeness and temporal position near the ancestor of a clade improved phylogenetic resolution as measured by the percentage of the tree-length distribution that contains the real tree. Furthermore, the conditions of completeness and temporal position under which fossil taxa improved phylogenetic resolution over living taxa became less restrictive as the rate of evolution or the temporal scope of the tree increased.
Molluscan diversification and extinction on opposite sides of the Isthmus of Panama
Authors: Jackson Jeremy B. C. , Jung Peter
Published: January 2018

Molluscs are the most diverse and abundant tropical American macrofossils, but their distributions and evolution are not well understood. Classic studies by Olsson and Woodring documented a rich Late Miocene to Early Pliocene “Gatunian” fauna throughout the Caribbean and tropical Eastern Pacific, with many species in common between the oceans. This fauna was divided by formation of the Isthmus of Panama, and diverged into distinct Pacific and Caribbean faunas sometime thereafter. Diversity also decreased by about half in the Caribbean. However, the timing, rates and correlation of these major biological changes with changes in environmental conditions have not been resolved because of imprecise dating and taxonomy and failure to consider problems of sampling and biofacies in biological comparisons. We used the newly revised late Neogene stratigraphy for Panama and Costa Rica to date for the first time the radiation and extinction of molluscs on opposite sides of the Isthmus. Data include occurrences throughout tropical America for nearly 100 species of the Strombina-group (Gastropoda, Columbellidae) and for more than 500 gastropod and bivalve genera from 240 Late Miocene to Pleistocene isthmian collections.

All evidence suggests that final closure of the Isthmus of Panama occurred between 3.5 and 2.5 My. Subgeneric divergence between the oceans was well developed, and trans-isthmian species were rare by the Early Pliocene, at least 2 Ma before final closure. Caribbean diversity remained high until 1.8 to 1.5 Ma when massive but selective extinction occurred. This was at least 1 Ma after final closure of the Isthmus, and may be correlated with onset of slightly cooler Caribbean sea surface temperatures in the Pleistocene. In contrast, Eastern Pacific diversity did not decline, and even increased during the Pleistocene.
Color in ostracode shells: taphonomy and paleotemperature interpretation
Authors: Kontrovitz Mervin , Slack Jerry Marie , Ainsworth Nigel R. , Burnett Richard D.
Published: January 2018

Interpretations of geologic history would be enhanced if taphonomic processes, including color changes in shells, were better known. This study deals with the origins and alteration of post-mortem colors in podocopid ostracodes. Modern shells were subjected to elevated temperatures and pressures in reactor vessels with sediments, simulating some burial conditions. Fossil shells from outcrops and boreholes were heated and treated with solvents, in an attempt to identify the coloring agent(s).

Modern marine shells are white to pale yellow (Munsell 5Y 8/1 – 2.5Y 8/4). Upon heating at atmosphere, up to about 650°, they became slightly redder, slightly darker, and less color saturated, but never dark (Munsell “value” less than 5). From 650-850° they became yellower and lighter, and above 850° chalky and more yellow. Shells at elevated temperatures and pressures (T-P) with organic-poor sediments and/or iron compounds developed higher color values and lower chromas; they did not become dark. Thus, modern ostracode shells subjected to elevated T-P changed colors, but alone never attained the dark colors seen in many fossils. Only those heated in matured organic-rich sediment and/or crude oils became dark (dark grays, browns, and blacks), like some fossils. Fossil ostracodes from boreholes in Mesozoic and Cenozoic sedimentary rocks showed downhole color differences similar to those from experiments. That is, the colors of fossils are different in hue, value and chroma in different thermal zones and ostracode color appears to be broadly indicative of thermal history.

Fossils near igneous intrusions are dark, while the lowered values and chromas of those in metamorphics also are correlatable with paleotemperatures. Reheated dark fossils lightened at about 375-450°, eventually becoming pale yellow to white, apparently indicating that organic coloring agents were driven off. This, and the fact that modern ostracodes develop dark colors only when heated in organic-rich substances, support the contention that the dark color originates from extrinsic organic materials. Pyritized shells become weak red (Munsell 10R 4/4) upon heating; thus, they can be distinguised from those colored by organics.

Therefore, ostracode colors appear to be diagnostic of T-P and present the potential for use in paleotemperature reconstructions. A wide range of fossils, including conodonts, phosphatic brachiopods, scolecodonts, and palynomorphs are known to show recognizable and useful evidence of thermal maturation and it is proposed that ostracodes be added to the list.
Biothems: sequence stratigraphic units and their implications for regional tectono-stratigraphic interpretations
Authors: Lane H. R. , Frye M. W. , Couples G. D.
Published: January 2018

Biothems are regional wedge- or lens-shaped bodies of strata that are: bounded shelfward or cratonward by paleontologically recognizable unconformities; generally thicken on marine shelves, where they are typically conformable with underlying and overlying biothems; are commonly thinner or represent “starved” sequences further basinward; and in their most basinward extent, are either bounded by biostratigraphically recognizable unconformities or are conformable with underlying and overlying biothems. Biothems are practical units whose definition and degree of refinement are dependent on the quality and availability of biostratigraphic control. As recognized to date, biothems have a logical distribution of faunal and floral components, as well as facies groupings that represent internally consistent and logical sequences of depositional environments. The use of biothems as primary sequence stratigraphic units places the emphasis on relative time in a stratigraphic framework.

A west-to-east transect within the North American Mississippian System, which extends from the Basin and Range Province, across the Transcontinental Arch (TA) and into the Anadarko Basin, was constructed to demonstrate the regional distribution and tectono-stratigraphic significance of biothems relative to the axis of the TA. The relationships portrayed on the transect, tied to an understanding of North American Mississippian paleogeography, imply that biothems deposited during relative highstand events on one flank of the TA are time-equivalent to biothems deposited during relative lowstand events on the opposite flank of the TA. This distribution is interpreted to have been controlled by intraplate tectonic events that formed “piano-key” basins along the flanks of the TA. The spatial patterns of these basins are not consistent with published models of basin evolution. A further conclusion is that the lack of transgressive or regressive coincident Mississippian biothems on either flank of the TA suggests that it is inadvisable to impose the Mississippi Valley-derived eustasy curve on western flank depositional sequences.
Paleoecology of Cyclocrinites darwini (Miller) - a cyclocrinitid alga from the Cincinnatian series (Upper Ordovician)
Authors: Lask Peter B.
Published: January 2018

Cyclocrinitids are considered to be calcareous green algae closely related to, or members of, the dasycladacean algae. Cyclocrinitids are characterized by a globular thallus 1-5 cm in diameter consisting of whorls of calcified meromes borne from a tubular or spherical central axis. The species Cyclocrinites darwini is distinguished from other cyclocrinitids by the presence of lateral branches arranged in a stellate pattern at the distal end of each merome.

C. darwini is restricted to strata of the Cincinnatian Series. Specimens are commonly found in shale-filled channels cutting through nodular, irregularly-bedded limestones within the Mt. Auburn Formation and the lower Sunset Member of the Arnheim Formation. Numerous specimens are also known from the Bellevue Member of the Grant Lake Formation at Maysville, Kentucky. Each of these units has been interpreted to be the top of separate shoaling-upward, third-order cycles. These facies are abundantly fossiliferous, often consisting of broken, abraded, and reworked material.

The modern dasyclad Neomeris is cited for its structural similarity to the cyclocrinitids and ecological parallels have been postulated as well. Neomeris and a similar dasyclad Batophora, thrive while attached to pieces of coral rubble at depths of less than 3 m in the high-energy conditions associated with a reef crest environment at Key Largo, Florida.

It is likely that C. darwini lived under similar conditions, attached to rubble in shoaling areas. Preservation only occurred in instances when thalli were broken off from their holdfasts and swept into ripple troughs or downslope channels cutting across the shoals. It has been suggested that the presence of cyclocrinitids is indicative of relatively quiet environments below wave base. For Cyclocrinites darwini, the opposite would appear to be the case.
Epibionts on Chlamys hastata and Chlamys rubida: taphonomic and paleoecologic implications
Authors: Lescinsky Halard
Published: January 2018

Although many fossil epibiont assemblages have been described, the taphonomy of these assemblages is poorly understood. In an effort to investigate the percentage of epibiontic organisms that would likely be preserved in the fossil record, and the contemporaneity of epibionts on a particular shell, I investigated the epibionts on live and dead Chlamys hastata and C. rubida from around San Juan Island, Washington. Using a video imaging system, over 300 shell surfaces were examined and the percent covers of epibionts in eight taxonomic categories were calculated.

The left (upper) valves of live Chlamys had an average epibiont cover of 75% that was composed primarily of sponge, or a combination of barnacles and sabellid annelids. The preservable portion of this assemblage (18%) was significantly less than that of epibionts on the exteriors (68%) and interiors (87%) of dead valves. On dead shell surfaces, sponge coverage is <1%, and there are higher proportions of cheilostome and cyclostome bryozoans, and serpulid and spirorbid annelids.

On upper surfaces (left valves) of living Chlamys, 10% of the epibiont cover was composed of dead organisms. An even greater percentage of dead epibiont cover existed on lower valves of live individuals (25%), and on dead valves (37-47%). During the study, no unambiguous examples of competitive interactions were found except for barnacles overgrowing barnacles and other epibionts. Numerous other overgrowths were observed, but these resulted from growths over dead organisms, or growths over mineralized skeleton, not living tissue.

These results suggest that exact contemporaneity between epibionts should not be assumed in paleoecological studies.and that soft bodied and agglutinating organisms may have been important constituents of some paleocommunities. Encrusting epibiontic sponge actually protects shell surface ornamentation and may be evidenced in the fossil record by particularly clean and unfouled shells.
The ecology of xenophyophores, an enigmatic group of agglutinating rhizopods
Authors: Levin Lisa A.
Published: January 2018

Xenophyophores are large, agglutinating protozoans whose modern distribution is limited exclusively to the deep sea (> 500 m water depth). Test morphologies vary from simple discoidal forms to elaborately folded or reticulated forms. Often specific particle sizes or minerals are selected for test construction. Tests are typically 1-5 cm in diameter, but some species may be up to 25 cm in longest dimension. Xenophyophores have been reported from a wide variety of soft- and hard-substrate deep-sea settings, including foram sands, calcareous and hemipelagic oozes, manganese nodule beds, fresh basalts, and hydrothermal oxides. They appear to obtain highest densities (often > 1/m2) on sloped substrates such as occur on seamounts, continental slopes, canyons, and trenches. Most xenophyophores live as epifauna on the sea floor and feed by actively or passively capturing suspended particles, but several species live as infauna and are presumed to be deposit feeders. It has been proposed that xenophyophores may garden bacteria within tests to provide an additional food source. Xenophyophores are distinguished from foraminifera by the occurrence of: (1) protoplasm encased within an organic membrane, (2) barite crystals within the protoplasm, and (3) tightly packed strands of fecal pellets (stercomare) within an organic membrane in the test.

Xenophyophore tests and surrounding sediments are known to be hotspots of metazoan activity in a variety of settings. Tests provide habitat and presumably refuge for many invertebrate groups, and sediments beneath epifaunal xenophyophore tests often exhibit elevated densities of macrofauna and meiofauna. Radiochemical studies suggest that xenophyophore tests are sites of enhanced particle flux to the seabed. Associated metazoans may be taking advantage of elevated food supplies in the vicinity of tests, or may be passively trapped by xenophyophore tests during dispersal stages.

Xenophyophores are not known from the fossil record. A resemblance between the infaunal xenophyophore Occultammina profunda and the trace fossil Paleodictyon has been noted by Swinbanks. Similar structures have been observed on the mid Atlantic ridge, but their identification as xenophyophores has not been confirmed. Maybury and Evans report a strong resemblance in external morphology, fine structure and barite content between modern xenophyophores in the genus Psammina and some Carboniferous phylloid algae, but fall short of suggesting a systematic relationship. Broader knowledge of xenophyophore morphology and ecology among ichnologists may lead to discovery of possible fossil antecedents. In addition, confirmation of xenophyophore presence could provide valuable information concerning paleohabitats.
Molecular taphonomy of plant tissue at the Miocene Clarkia site, northern Idaho
Authors: Logan Graham
Published: January 2018

The 17–20 million year old Miocene locality at Clarkia, northern Idaho, has become renowned as the first site to yield amplifiable DNA of geological age. This discovery has opened up the possibility of phylogenetic studies on fossil tissue using preserved DNA. However, the conditions required for DNA preservation in the fossil record are not understood. An organic geochemical study of fossil tissue and sediments has been undertaken at the Clarkia site to assess the preservation of other less labile compounds, such as leaf waxes, structural polysaccharides, cutins, lignins and chlorophyll pigments. Previous organic geochemical studies have developed an understanding of the behaviour of these compound classes in different environments. The relative behaviour of the compound classes and the preservation of individual compounds within each class can therefore help in the interpretation of the biogeochemistry of this site which may in turn shed light on the reported preservation of fossil DNA.

Leaf waxes are preserved but a selective loss of long chain esters has occurred, and microbial degradation products of triterpenoids have been identified. Structural polysaccharides and cutins have been lost from the leaf tissues. A highly resistant aliphatic polymer is preserved in the mesophyll and epidermal regions of the leaves, with lignin identified in leaf vein tissues. Various degradation products of chlorophyll have also been identified. The organic geochemical results are all consistent with microbial degradation within the leaf tissues and sediment. Excellent morphological preservation is not accompanied by mutual chemical preservation. The survival of DNA in this environment is extremely surprising. However, preservation of plant polyphenols may provide an answer to this anomaly.
Accelerated development in planktonic foraminifera: adaptive response to reduced ocean mixing
Authors: Lohmann G. P.
Published: January 2018

Planktonic foraminifera grow by adding chambers to their shells, increasing shell size and changing shell shape. Shell development can be distinguished from shell size either by counting the chambers or by measuring the allometry associated with developmental shape changes. It is necessary to make this distinction when trying to understand the life history adaptations of planktonic foraminifera to their environment because there is wide variation in shell size among individuals at the same stage of development.

While the life cycle of many species of planktonic foraminifera is adapted to the monthly lunar cycle, certain deep-living species such as Globorotalia truncatulinoides and G. hirsuta are adapted to the annual cycle of late winter nutrient upwelling and spring bloom, the mechanism that drives primary productivity in subtropical latitudes. These deep-living species grow while sinking from the surface ocean through the upper 500 to 1000m of the water column and then reproduce at depth. Juveniles must somehow return to surface waters.

For such a life cycle, size may affect reproductive success in two opposing ways: while the number of gametes produced is directly proportional to size, the bouyancy of the offspring and so the likelihood that they will reach surface waters are inversely proportional to size. The balance between the reproductive benefits of large size and the difficulty of returning large juveniles to surface waters can be altered by vertically mixing the water column. The deep mixing that brings nutrients to surface waters can also help juvenile foraminifera reach the surface.

Today the largest shells of G. truncatulinoides are found in populations growing on the poleward margins of the subtropical gyres, areas where the scale of mixing is greatest. As the vertical scale of this mixing decreases toward the tropics, shells at each stage of development shift toward smaller average sizes. This apparent acceleration in development reflects a loss of large shells, which decreases both the average size and the overall abundance of the species.

The relationship of apparent developmental rate to the scale of vertical mixing produces the previously reported “ecophenotypic cline” in which G. truncatulinoides changes from a compressed biconvex form in high latitudes to a highly conical form in the tropics. By design, the study reporting this observation was based on shells from a narrow range of size in an attempt to minimize any developmental sources of morphologic variation. Paradoxically, this strategy focussed observations on the systematic shift in the relationship between shell size and development caused by differences in upper ocean mixing. The apparent cline consists of shells of the same size but at different stages of development. A similar explanation may account for the apparent gradual “evolution” observed in G. truncatulinoides during the Late Pleistocene.
Lyginopterid seed ferns in basal Upper Carboniferous marine black shale deposits of midcontinent North America
Authors: Mapes Gene , Rothwell Gar W. , Cook Jeremy G.
Published: January 2018

Permineralized plant remains occur individually and in small mats within anoxic and dysoxic marine black shales deposited seaward of the Wedington delta (Fayetteville Formation, Middle Chester) in northwestern Arkansas. Plant debris and associated cephalopods occur within 20 km of offshore bars that developed at the mouths of delta distributary channels. The bars were produced by longshore paleocurrents flowing eastward among the southwestern margin of the Ozark Dome. The flora includes several genera of arborescent lycopods, zygopteridalean ferns, filicalean ferns, calamites, medullosan seed ferns and seed fern remains with features that are characteristic of the Lyginopteridaceae. Among the lyginopteridalean stems are specimens that have been described as Megaloxylon wheelerae, an arborescent form, as well as several undescribed species.

Two stems with prominent leaf scars represent one species of a new genus. The stems measure 35 cm and 34 cm long, and are approximately 2.5 cm in diameter. Leaf arrangement is helical, approaching a 3/8 phyllotaxis, with internodal lengths of about 3 cm. Stems are eustelic with a polygonal primary body 3-4 mm in diameter. Each leaf trace diverges from the cauline bundle as a single strand. The strand trifurcates in the cortex to produce a distinctive configuration of two c-shaped lateral bundles separated by a tangentially elongated central strand.

Pith cells are large with prominent walls. Some show internal contents suggestive of secretory substances. The primary body is surrounded by a distinctive zone of wood 3-4 cm wide. Large rays 2-5 cells wide and more than 8 mm high separate wedges of tracheids that typically are 2-4 cells wide. Secondary tracheids display multiseriate oval bordered pits on the radial walls. Vascular cambium and secondary phloem are present, but incompletely preserved. The cortex is differentiated into an inner parenchymatous zone with horizontally elongated “sclerotic” nests, and an outer zone of alternating bands of vertically elongated sclerenchyma and parenchyma.

This material significantly increases our knowledge of Namurian floras inhabiting non peat-forming environments, and emphasizes the systematic diversity among hydrasperman gymnosperms at the base of the Upper Carboniferous.
Upper Carboniferous ammonoid embryonic shell clusters: transported accumulation or

in situ

nests?
Authors: Mapes Royal H. , Tanabe Kazushige , Landman Neil H. , Faulkner Curtis J.
Published: January 2018

Clusters of ammonoid embryonic shells have been discovered in several carbonate concretions from a dysoxic, relatively deep water shale (Heebner Shale-Oread Formation) of Virgilian (U. Carboniferous) age near the community of Pomona, Kansas. The concretions from a single outcrop display four distinct units. Unit 1 is the lowest unit and has an evenly laminated fabric with scattered embryonic and juvenile ammonoids, gastropods, and bivalves. The bedding fabric of this unit is interrupted and truncated by a series of pits that form the base of Unit 2, which is a sharply bounded discontinuity. Within the pits there are embryonic ammonoid clusters up to 2.5 cm thick containing as many as 250 individuals per cm3. Some juvenile ammonoids and shell fragments (mostly of ammonoids) are also present. These clusters are capped by Unit 3 which has a gradational boundary with Unit 2. Unit 3 consists in places of a packstone of fossil debris including ammonoid body chamber and phragmocone fragments, three genera of juvenile ammonoids, embryonic ammonoids, and more rarely brachiopods, bivalves, and orthoconic nautiloids. Elsewhere, fossils of Unit 3 are well separated by matrix, which lacks the bedding fabric characteristic of Unit 1. The ammonoids in Unit 3 include mature to sub-mature fragments of Aristoceras and sub-mature phragmocones of Glaphyrites and Shumardites. The brachiopods (articulate and inarticulate) and the bivalves are probably sub-mature or mature. Planktonic bivalves are extremely rare. The number of shell fragments of embryonic and postembryonic ammonoids and other shell fragments decreases upwards from the upper contact of Unit 2. The boundary of Units 3 and 4 is more-or-less gradational; Unit 4 has a sedimentary fabric and faunal content like that observed in Unit 1.

One set of hypotheses to explain the embryo clusters in Unit 2 emphasizes sedimentological processes such as selective transportation and accumulation by currents, turbidity transport and storm deposits. Another set of hypotheses favors biological activities such as reproductive activity and egg-laying. If this second set of hypotheses is correct, these clusters would provide the first documentation of ammonoid reproductive activity and would represent a find as significant in its way as that of the nests of embryo bearing dinosaur eggs.
Trophic structure of the Lower Oxford Clay
Authors: Martill David M. , Duff Keith L. , Bown Paul R.
Published: January 2018

Conventional palaeontological methodology over the last one hundred years has revealed a complex and intricate food web in the Jurassic Lower Oxford Clay of central England; we are able to identify the top carnivores (pliosaurs) down to the primary producers (coccolithophoroids) within the water column. In some cases it is even possible to identify individual prey preferences for different taxa.

What conventional palaeontology cannot do satisfactorily is determine the quantities of food processed through the food web, the source of the nutrients, and how much and where recycling of nutrients took place. Consequently we here combine the results of extensive fossil collecting, begun in the 1890s, with data obtained from organic geochemical analysis and isotopic analysis of Oxford Clay sediment and its preserved biota (shells and bones). Examples follow:

Palaeotemperatures derived from vertebrates show that ichthyosaurs, plesiosaurs and crocodiles were calcifying in waters with temperatures in the range (190 – 220). In addition, the giant filter feeding fish Leedsichthys also yields palaeotemperatures in this range, suggesting that it was a pelagic filter feeder exploiting a rich surface plankton source.

Direct evidence for tetrapod diet in the form of preserved stomach contents indicates that hookleted cephalopods formed an important food source for macrovertebrates (Martill 1986). Isotopic data indicate that belemnites (believed to have been hookleted) were living in the lower water column (T = 150). We suggest that perhaps belemnites migrated to surface waters for feeding (probably at night) where they were predated upon by marine reptiles.

Duff (1978) suggested that the bivalves Bositra and Meleagrinella lived attached to seaweed rather than living directly on a dysoxic, probably soupy, sea floor. Isotopic data gives palaeotemperatures from these bivalves in the range 16-18 C, comparable with the range 15-18 C derived from the definitely benthic bivalve Gryphaea. Clearly if Meleaqrinella and Bositra lived attached to seaweed then the bottom of the Oxford Clay Sea lay within the photic zone. Organic geochemical analysis indicates high nutrient input, and this is reflected in an extremely high abundance, and diversity peak, for Boreal Jurassic nannofossils.
Secular variation in microfossil preservation: causes and consequences of the biogeochemical evolution of the oceans
Authors: Martin Ronald E.
Published: January 2018

Because of their abundance, composition, and widespread occurrence throughout the Phanerozoic, microfossils are ideal subjects for teasing apart the ecological, evolutionary, geochemical, and taphonomic controls on the fossil record, and for testing hypotheses of evolutionary paleoecology against secular change in ocean chemistry as evidenced by patterns of fossil preservation. The history of calcareous plankton is one of interaction between the evolutionary innovation of regulatory pathways in hardpart construction and the paleochemistry of the seas. Diversification of ancestral shelfal calcareous plankton lineages in the Mesozoic was related to sea level transgression, water column stratification, and habitat diversity, as evidenced by major expansions of these groups in association with Oceanic Anoxic Events. In the case of coccolithophorids (calcareous Haptophyceae), the origination of calcified lineages also appears to have been related to nutrient resuspension from bottom sediments and anoxic waters (which may have promoted calcification) advected into the photic zone over shallow shelves during transgressions. Invasion of pelagic habitats by Foraminifera was facilitated by the evolution of test secretory mechanisms (beginning in the Late Paleozoic) that conferred greater cellular control over shell microstructure and density. The beginnings of calcareous nannoplankton, however, are traceable to microfossil “Lagerstätten” that hint at the first attempts at calcification by naked haptophycean lineages much earlier in the Paleozoic. During the Early-Mid Paleozoic greenhouse phase, calcareous nannoplankton assemblages were unlikely to be preserved because high levels of atmospheric (and therefore oceanic) CO2 and extraction of CaCO3 in epeiric seas by calcareous biota resulted in a very shallow CCD. With the advent of the Late Paleozoic icehouse phase (and associated sea level fall), the locus of biogenic limestone deposition shifted seaward and the CCD deepened. Significant accumulations of calcareous pelagic sediments followed in the Late Jurassic in response to diversification of calcareous plankton. As deep pelagic oozes began to accumulate, a new component was added to the global carbon cycle: the metamorphic decarbonation of pelagic limestones that controls long-term (i.e., tens to hundreds-of-millions of years) global warming.