bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
Foraminiferal turnover in neritic environments in the Oligocene of Southern Australia
Authors: Moss Graham D. 
Published: January 2018

This study explores an excellent mid-latitude Oligocene calcareous neritic succession that spans the Eocene/Oligocene boundary to the Miocene. Rapid changes in sea level and climate should have a palpable influence on macroevolution and the Eocene-Oligocene transition marks one of the most substantial changes for the Cainozoic.Stratigraphic ranges of some 130 benthic and 20 planktic species occurring in two contrasting marine environments, one relatively restricted (low plankton - Murray Basin) and another more open (high plankton - Otway Basin) to oceanic processes, were identified and correlated with signals derived from changes in the physical environment. The signals include: the ‘Exxon’ sea-level curve, deep sea stable isotope curves, and prominent lithological changes.There is a significant turnover of species at the Eocene/Oligocene boundary. This event impacts on all assemblages and correlation metrics indicate that there is an ‘across-the-board’ response. Interestingly, the turnover corresponds to a local Saint Vincent Basin lithological change from the grey-green, organic rich facies of the Blanche Point Formation to the red-yellow-brown, well oxidized, quartz and bryozoa rich facies of the Port Willunga Formation. This switch is in turn coincident with the saltatory positive deviation in the δ18O top and bottom water curves derived from oceanic sections.The turnover pattern is not repeated at the major sea level fall predicted for the mid Oligocene (at 30 million years), neither is there any comparable lithological transition. Geographically widespread species (common to all environments) cross this supposed prominent type one sequence boundary, there is a signal but the impact on the fauna is less than that detected for the Eocene/Oligocene boundary. Those faunas that were more restricted to open ocean processes exhibited shorter stratigraphic ranges and appeared to be controlled primarily by sea level fluctuation and salinity changes. There is evidence to suggest that foraminiferal faunas of the more restricted environment in southern Australia were less responsive to the well mixed, thermohaline driven ocean of the Oligocene. Generally, Oligocene benthic assemblages are dominated by Cibicides, Notorotalia and Buliminid species in consistently high numbers, indicating a high dominance of relatively few taxa, that is, large populations and low diversity. Faunas of open ocean assemblages demonstrate relatively subdued turnover patterns compared to those of more restricted environments.The Late Eocene displays parallel patterns of foraminiferal turnover and the Oligocene is characterised by inter-basin contrasts. In comparison to the Eocene, faunas appear to be more robust in the psychrosphere constrained ocean of the Oligocene. It is proposed that these patterns indicate that the Latest Eocene was dominated by species adapted to a specialist life strategy while the Oligocene reflect patterns more often associated with opportunist colonization.
Long survival of stalk pieces of Metacrinus rotundus Carpenter, a modern stalked crinoid, in an aquarium
Authors: Oji Tatsuo , Amemiya Shonan 
Published: January 2018

Previous underwater observations have demonstrated that detached stalk pieces with a few noditaxes are often found in the habitats of modern isocrinid crinoids. They sometimes stand on the substrate by grasping hard objects by cirri. According to the growth of the stalk, the distal parts are repeatedly detached from the main body and discarded on the sea floor. There has been no information about the “fate” of such isolated stalk pieces. Abundance of stalk pieces of crinoids in the geologic column must be considered with reference to the modern analogue.We have collected by dredging specimens of modern stalked crinoid Metacrinus rotundus Carpenter from the depths of 135-150 m in Suruga Bay, central Japan. Specimens were transferred to a large temperature controlled aquarium (13°) within several hours after capture. While keeping the animals, a few specimens have autotomized the distal stalk, and isolated pieces with a few noditaxes were left in the aquarium. They have kept the same postures and still attached to pebbles by cirri for approximately one year. No further disarticulation nor regeneration occurred to the stalk pieces.Section of the stalk piece stained by hematocyanin showed that the nuclei were well colored and the fragmental stalk was considered as living. This result strongly suggests a possibility that such fragmental stalks can live for a long time in the natural environment. Abundant occurrence of stalk elements from the geologic record have been attributed to a taphonomic process; selective accumulation of a part of the body after death, but the present results imply that these stalk pieces could live alone for a long time on the sea floor.
Paleoclimate, controls on Upper Devonian source rock sequences and stacked extinctions
Authors: Ormiston Allen R. , Klapper Gilbert 
Published: January 2018

High quality (>2% TOC) Upper Devonian source rocks are developed in several sequence types. The commonest type, accounting for 70% of the studied examples is the transgressive sequence with a basal hiatus. Others include shallowing upward sequences (12%), lacustrine sequences in fault-controlled basins (7%), distal slope sequences (7%), and evaporite capped sequences (4%).Starting from the synthesis of Johnson, Klapper, and Sandberg (1985) it has been possible to demonstrate correlativity of Upper Devonian transgressive episodes globally. The marked association of epeiric sea Upper Devonian source rocks with transgressions heightens interest in their causation. Could they have been produced by glacio-eustatic sea-level change as Stanley (1984; 1988) implies? Quantitative paleoclimate modeling and isotopic paleotemperatures for the Upper Devonian suggest not. Modeling using CCM1 at NCAR, including five year seasonal cycles, suggests the absence of any large southern hemisphere ice volume. Because much of the Upper Devonian land mass was either in equatorial or high latitude regions, there was little development of monsoonal climates. Midlatitude cyclonic activity was also much less than at present, meaning less polar transport of moisture and drier polar areas. Precipitation maxima largely coincided with topographic elevations. In contrast to the Late Ordovician to earliest Silurian, there was no Upper Devonian perennial snow cover even over the high latitude southern land mass. This was in spite of winter land temperatures as low as -40°. in eastern Gondwana. In that area and elsewhere, there was thin winter snow cover which melted in late spring resulting in no build-up of snow cover to produce glaciation. This was mainly the consequence of low winter precipitation in Gondwana. High latitude sea surface temperatures were certainly cold enough to displace or exclude some organisms. However, in low latitude areas where Upper Devonian extinctions also took place, modeled sea surface temperatures range between 27° and 34°. Such areas would have been refuges for any organisms displaced by cold, high latitude waters. The higher temperature values of low latitudes are convergent with the isotopic paleotemperatures determined by Brand (1989) using well preserved Upper Devonian brachiopods. Brand's determinations suggest temperatures even reaching lethal values for many plankton (37°). The extinction of reefs by the close of Frasnian time could have been partly a result of such elevated temperatures. Stacked extinctions of conodonts (Ziegler and Lane, 1987) and acritarchs may have been a further result. The loss of reefs, an important consumer of plankton, may have permitted a relative increase in plankton abundance crossing from more oceanic areas into epeiric seas, possibly contributing to high quality source rock deposition.
The Sirius Passet Fauna, an Early Cambrian Lagerstätte from North Greenland
Authors: Peel John S. , Conway Morris Simon , Ineson Jon R. 
Published: January 2018

The Sirius Passet Fauna of North Greenland is one of the oldest Cambrian lagerstätten from the North American continent. It is known from a single locality in Peary Land (83°N, 40°W), on the shores of the Arctic Ocean, where outer shelf mudstones from the lower part of the Buen Formation (Early Cambrian) yield a rich assemblage of mainly poorly skeletised organisms with preserved soft parts. The steeply-dipping fossiliferous mudstones occur in close proximity to horizontally-bedded platform carbonates of the underlying Portfjeld Formation (Early Cambrian) in a structurally complex terrane. The boundary between the fossiliferous mudstones and the platform carbonates apparently defines the original northern margin of the carbonate platform and is not, as previously suggested, a structural feature, although some minor tectonic modification can not be excluded. Thus, the fossiliferous mudstones were apparently deposited in a transitional slope setting basinward of the shelf edge.As currently known, the Sirius Passet Fauna comprises about 40 species, based on a collection of almost 5,000 slabs collected during brief visits to the isolated locality in 1989 and 1991. Arthropods dominate, with bivalved bradoriids and the trilobite Buenellus higginsi Blaker, 1988 being the numerically most abundant taxa. Weakly skeletised Naraoia-like and Sidneyia-like arthropods often preserve limbs and gills, as do bivalved arthropods similar to Waptia. Choia is the most common of several sponges. Worms include both priapulids and polychaetes, with a large palaeoscolecidan being conspicuous.Fully articulated specimens of halkieriid worms, clad in an armour of hundreds of individual sclerites, are most notable amongst several problematic taxa. Rare specimens of possible onychophorans are also present, while brachiopods, hyoliths and other shelly fossils are rare or absent.The Sirius Passet Fauna seems to show little taxonomic similarity to the Middle Cambrian Burgess Shale of western Canada or the Chengjiang Fauna from the Lower Cambrian of China at the generic level. Together with the latter fauna, however, it confirms both the general picture of Cambrian life presented by the Burgess Shale, and the existence of this great diversity of weakly skeletised arthropods already in the Early Cambrian.
Comparative physiology of suspension feeding in living articulate brachiopods and bivalves - implications for large-scale evolutionary patterns
Authors: Rhodes Melissa C. 
Published: January 2018

The hypothesis that biotic interactions have escalated over geologic time suggests that taxonomic groups such as bivalves, which developed representatives with high-energy life habits, preempted resources and drove “obsolete” low-energy groups, such as articulate brachiopods, into ecological refugia. Articulates had been the dominant benthos in a broad range of Paleozoic habitats. Modern refugia include areas of darkness and low primary productivity, such as fjords, caves, and polar regions. If the escalation hypothesis is true, then the modern articulates concentrated in these habitats should have extremely low energy budgets. The more energetic bivalves should be abundant higher in the photic zone and have higher energy budgets.The equation Consumption = Growth (metabolizing tissue) + Reproduction + Respiration + Faeces + Excreta (nitrogenous) describes the energy balance in an organism. Energy acquisition is a critical factor for the persistance of individuals and species. Scaling equations relating particle filtration rates (consumption) to tissue mass were developed experimentally for two northern and two southern hemisphere species of brachiopods. Similar equations were developed for a northern and a southern hemisphere mussel species. The scaling equations allow correction for size differences which would otherwise confound physiological comparisons between species. Both northern and southern hemisphere brachiopod species were collected from deep, dark fjords or soft bottom habitats with Paleozoic style faunas. The mussels were collected from the same areas, but occurred higher in the photic zone.Results indicate that the articulate brachiopods have a significantly lower ability to collect food particles from the water than do the mussels, for animals of similar body mass. These results support the hypothesis that escalated biotic interactions account, in part, for the ecological replacement of the formerly dominant Paleozoic articulate brachiopods by Mesozoic and Recent suspension-feeding bivalves.
Role of microorganisms in the production of lime mud and implications for interpretation of ancient micrite deposits
Authors: Robbins L.L. , Yates K. 
Published: January 2018

Geologists have long been plagued by the lack of evidence for the origin of ancient micrite deposits: any paleontological evidence is typically obscured or lacking altogether. The role of modern marine picoplankton gives insight into the origin of one mode of lime mud formation and may aid in the interpretation of ancient marine deposits.Whitings, patches of floating lime mud in supersaturated seawater on carbonate platforms, obtained from the Bahama Bank were analyzed utilizing biochemical techniques and Transmission Electron Microscopy. All Whitings indicated a close association between picoplankton cellular material and calcium carbonate crystals. Culture experiments indicated the presence of at least ten different picoplankton species in Whitings water. Two major genera found were the blue-green algae, Synechococcus and Synechocystis. Field and laboratory experimental data indicated that these cells and cellular organics play a major role in Whitings formation. The cells may undergo epicellular precipitation of calcium carbonate induced by photosynthesis. Environmental conditions necessary for this process have been delineated through field data and laboratory experiments.While picoplankton organics are rarely preserved over geologic time, the product of their life habit, namely lime mud, is preserved as micrite. Thick occurrences of micrite deposited in marine environments are widespread throughout the geologic record, ranging in age from Precambrian to Recent. Although rare, fossilized blue-green algae have been observed in Archean rocks and may be the only evidence that implicates these organisms in lime mud formation. The Whitings phenomenon serves as an excellent example in which a specific type of organism may be a prolific contributor to the rock record, and yet leaves no direct paleontological evidence of its involvement.
Early angiosperm fossil leaves in Chubut Group, Cretaceous, Argentina
Authors: Romero Edgardo J. , Palma Ricardo 
Published: January 2018

The oldest angiosperm leaves from Patagonia were reported from Baquero Formation (Barremian-Aptian) in a mesofitic flora of more than one hundred gymnosperm and fern species. The next younger records are from the Chubut Group, a thick assemblage of pyroclastic sediments, with sand and conglomerate facies and frequent paleosols. In the Sierra de San Bernardo area sediments are mainly tufaceous and fluvial, deposited under an arid climate in shallow lakes and swamps of the alluvial plains. The sea was hundreds of kilometers to the West. Four Formations were described: Matasiete (Aptian), Castillo and Bajo Barreal (Senonian) and Laguna Palacios (Campanian-Maastrichtian). We explored in the Senonian Formations, and studied a few outcrops that can be sorted as:a) Monospecific, with only Onychiopsis sp., in palustral sediments. b) Strongly dominated by Eauisetum sp, and few remains of two dicot species with large, entire margined, low rank leaves, in palustral sediments. c) Strongly dominated by two species of angiosperms with small leaves, associated with remains of conifers in tufaceous beds deposited in the alluvial plain. d) Dominated by a few species of dicots, with medium size, entire margined leaves. Also with about 10 species of ferns, gymnosperms and lobate angiosperms. They are in alluvial plains sediments. e) More balanced associations, with several abundant species, including angiosperms with lobate and leaves. They are in fluvial sediments.Although angiosperm radiation and taphonomy undoubtedly accounts for differences of plant composition between outcrops, it seems apparent that the record of early angiosperms in Chubut Group is represented by remains of many different plant associations, with few species, adapted to different environments, that probably coexisted, and developed under an arid climate, far from the sea.
Paleobiology of the Ediacara Fauna
Authors: Runnegar Bruce 
Published: January 2018

Long regarded as the earliest evidence for animal life, the fossils of the Ediacara fauna have come under increasingly close scrutiny as the result of a proposal made by A. Seilacher in 1983. At that time Seilacher suggested that the Ediacara fauna represents an extinct line of animal life (the Vendozoa) which pioneered a body form and modes of nutrition not seen in the Phanerozoic. More recently, Seilacher and others have suggested that most typical members of the Ediacara fauna were not even animals but were extinct foliate creatures analogous to algae or fungi which relied on endogenous photosymbionts or chemosymbionts for food and energy.It would not be surprising if the Ediacaran organisms contained bacterial or eukaryotic endosymbionts as endosymbiosis at the organelle or unicell level is the norm rather than the exception for many protists and diploblastic metazoans. However, it is difficult to find the evidence to test this endosymbiont hypothesis because the Ediacaran fossils are merely impressions of soft bodies in sandstone or siltstone.As there are no clear modern homologs of most of the Ediacaran organisms it is necessary to resort to logic and experiment to understand them. This has proved to be a formidable task but some progress is being made with complex forms such as Dickinsonia and Phyllozoon. Although no core member of the Ediacara fauna is unequivocally an early animal, there are more similarities to animals than to algae or fungi. There is no evidence at all that the vendozoans are fourth form of eukaryotic multicellular life.