Papers by James Schiffbauer
PalZ, 2020
The middle Cambrian (Miaolingian Series; Wuliuan Stage) Spence Shale of Utah and Idaho preserves ... more The middle Cambrian (Miaolingian Series; Wuliuan Stage) Spence Shale of Utah and Idaho preserves a diverse assemblage of biomineralized and soft-bodied taxa. Among the rarest specimens of this fauna are palaeoscolecid worms. Until recently, only one specimen was known from the Spence Shale, the holotype specimen of Palaeoscolex ratcliffei Robison, 1969, later included in the genus Wronascolex. This specimen is preserved as part and counterpart but missing both the posterior and anterior terminations. A new specimen, discovered by Riley Smith, preserves an everted proboscis with spines. Based on new data collected using scanning electron microscopy and energy dispersive X-ray spectrometry (SEM-EDS), and optical microscopy, the species is thought to represent a new genus, Utahscolex gen. nov., rather than a species of Palaeoscolex or Wronascolex as previously suggested. The new genus differs from the other two genera in the lack of node ornamentation of the plates, as well as the absence of microplates and platelets. Based on this case study, it is recommended that future revisions of palaeoscolecid taxonomy require knowledge of plate, platelet, and microplate ornamentation, as well as the arrangement of the plates, platelets, and microplates on the cuticle. In addition to the improved morphological information provided by the new specimen, it also advances our knowledge of the taphonomic pathways in the Spence Shale and in palaeoscolecid worms in general. The preservation of the plates of the two specimens of this species differ in elemental composition and somewhat in quality. While both the holotype and new specimen show localized magnesium and phosphorus within the plates, the holotype has a substantial iron component, whereas the new specimen instead shows elevated calcium. In addition, kerogenization, pyritization, aluminosilicification, and phosphatization can be observed throughout the specimen. The preservation varies not only between the specimens, but also within, demonstrating the high variability of preservational pathways within a Burgess Shale-type deposit, and providing insights into the circumstances that lead to soft-bodied preservation in the Spence Shale.
Earth's earliest biosphere is known from carbon and sulfur isotopes in rocks of Eoarchean (3.... more Earth's earliest biosphere is known from carbon and sulfur isotopes in rocks of Eoarchean (3.85 to 3.6 Ga) ages. However, fossils or biogenic structures of this antiquity have not been found. We have identified a preserved sandy tidal flat from the > 3.7 Ga Isua Greenstone Belt (IGB), Greenland, in which quartzite and metapelite rocks define original tidal sedimentary beds.
Circular graphite discs, among abundant irregular graphite particles, have been extracted from Ar... more Circular graphite discs, among abundant irregular graphite particles, have been extracted from Archean- Paleoproterozoic amphibolite grade metamorphic rocks in the Wutaishan area of North China. Raman spectroscopic analysis indicates that these graphite discs experienced maximum metamorphic temperature of 513 ± 50 °C. The discs bear morphological features related to metamorphism, but they are also characterized by circular morphology, distinct marginal
PALAIOS, 2008
Drill holes in prey skeletons are the most common source of data for quantifying predator-prey in... more Drill holes in prey skeletons are the most common source of data for quantifying predator-prey interactions in the fossil record. To be useful, however, such drill holes need to be identified correctly. Field emission scanning electron microscopy (FE-SEM) and environmental scanning electron microscopy (ESEM) were applied to describe and quantify microstructural characteristics of drill holes. Various specimens, including modern limpets and mussels drilled by muricid snails in laboratory experiments, subfossil limpets collected from a tidal flat (San Juan Island, Washington state, USA), and various Miocene bivalves collected from multiple European sites, were examined for microstructural features. The microstructures observed are interpreted here as Radulichnus-like micro-rasping marks, or predatory microtraces, made by the radula of drilling gastropod predators. The mean adjacent spacing of these microtraces is notably denser than the spacing of muricid radular teeth determined by measurements taken from the literature. Because the radular marks typically overlie or crosscut each other, the denser spacing of predatory microtraces likely reflects superimposition of scratches from repeated passes of the radula. One incomplete drill hole showed a clear, chemically aided drilling dissolution signature around its outer margin, while a number of other specimens showed similar, but ambiguous, traces of dissolution. The range of organisms examined illustrates the utility of scanning electron microscopy (SEM) imaging for identifying micro-rasping marks associated with predatory drill holes in both modern and fossil specimens. These distinct microtraces offer promise for augmenting our ability to identify drill holes in the fossil record and to distinguish them from holes produced by non-predatory means.
PALAIOS, 2010
... whereas biostratinomic processes of Precambrian Lagerstätten have not been extensively studie... more ... whereas biostratinomic processes of Precambrian Lagerstätten have not been extensively studied. In this paper, we provide a taphonomic framework for the Ediacaran Gaojiashan Lagerstätte in southern Shaanxi Province of South China, with a focus on biostratinomythe ...
Topics in Geobiology, 2011
Coupled dual-beam focused ion beam electron microscopy (FIB-EM) has gained popularity across mult... more Coupled dual-beam focused ion beam electron microscopy (FIB-EM) has gained popularity across multiple disciplines over the past decade. Widely utilized as a stand-alone instrument for micromachining and metal or insulator deposition in numerous industries, the submicron-scale ion milling and cutting capabilities of FIB-EM systems have been well documented in the materials science literature. These capacities make FIB-EM a powerful tool for in situ, site-specific transmission electron microscopy (TEM) ultrathin foil preparation. Recent advancements in the field-emission guns (FEGs) of FIB-EM systems have provided spatial resolution comparable to that of many high-end scanning electron microscopes (SEM), thus providing enhanced imaging capacities with material deposition and material removal capabilities. More recently, FIB-EM preparation techniques have been applied to geological samples to characterize mineral inclusions, grain boundaries, and microfossils. Here, we demonstrate a novel method for analyzing three-dimensional (3-D) ultrastructures of microfossils using FIB-EM. Our method, FIB-EM nanotomography, consists of sequential ion milling, or cross sectioning, and concurrent SEM imaging. This technique with coupled dual-beam systems allows for real-time, 3-D ultrastructural analysis and compositional mapping with precise site selectivity and may provide new insights in fossil ultrastructures. Using the FIB-EM nanotomography method, we investigated herkomorphic and acanthomorphic acritarchs (organicwalled microfossils) extracted from the $999 Ma Mesoproterozoic Ruyang Group of North China. The 3-D characteristics of such important but controversial acritarch features as processes and vesicularly enclosed central bodies are described. Through these case studies, we demonstrate that FIB-EM nanotomography is a powerful and useful tool for investigating the three-dimensionality of microfossil ultra-and nanostructures.
PALAIOS, 2012
While the study of taphonomic processes has elucidated numerous biases within the fossil record o... more While the study of taphonomic processes has elucidated numerous biases within the fossil record of life on Earth (for recent examples, see contributions within Allison and Bottjer, 2011), perhaps the most striking example comes in the form of preserved soft tissues and softbodied organisms. Deposits with these exceptionally conserved tissues, known as Konservat-Lagerstätten (Seilacher, 1970), represent one of the richest sources of paleontological data available in the fossil record. Yet, these exceptional faunas have ...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2014
A new ichnogenus and ichnospecies, Lamonte trevallis, is formally described from the Shibantan Me... more A new ichnogenus and ichnospecies, Lamonte trevallis, is formally described from the Shibantan Member limestone of the upper Ediacaran Dengying Formation, Yangtze Gorges area, South China. It is characterized by horizontal tunnels connected with short vertical burrows and surface trails. The horizontal burrows are elliptical or bilobed in transverse cross-section, preserved in full relief, and filled with carbonate intraclasts, micrites, as well as calcite and silica cements. They occur exclusively in silty, crinkled, and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats; no burrows have been found in intraclastic layers adjacent to the microlaminated layers. The vertical traces are filled with the same material as the burrows, but they typically project through the crinkled microlaminae and are exposed on the bedding surface. The surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs. The burrow infill has δ 18 O carb and δ 13 C carb values distinct from, but intermediate between, microlaminated and intraclastic layers, consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements, intraclasts, and micrites. Bedding plane bioturbation intensity (20-40%)-measured as percentage of bedding plane area covered by L. trevallis traces-is comparable to similar measurements in pre-trilobite Cambrian carbonates. The exclusive occurrence of L. trevallis within microbial mats may have both taphonomic and ecological significance. These mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows, and they may have also facilitated early diagenetic cementation of burrow infill, thus facilitating burrow preservation. The close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources. The trace makers of L. trevallis were better able to utilize the resources around them than many other Ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late Ediacaran oceans at the dawn of the agronomic revolution.
Burgess Shale-type (BST) fossils often are preserved as two-dimensional carbonaceous compressions... more Burgess Shale-type (BST) fossils often are preserved as two-dimensional carbonaceous compressions, sometimes aided by two mineralization processes: pyritization and aluminosilicification, defined by a thin and sometimes localized coating of authigenic pyrite or aluminosilicate minerals on the carbonaceous materials.
Precambrian Research, 2011
Seawater temperatures throughout Earth's history have been suggested to illustrate a long-term co... more Seawater temperatures throughout Earth's history have been suggested to illustrate a long-term cooling trend from nearly 70 • C at ∼3500 Ma to around 20 • C at ∼800 Ma. The terminal Neoproterozoic prior to the "Cambrian Explosion" is a key interval in evolutionary history, as complex multicellularity appeared with the advent of the Ediacara fauna. These organisms were likely the first that required higher levels of atmospheric and dissolved marine oxygen for their sustainability. It is known that most modern macroinvertebrates are intolerant of temperatures in excess of 45 • C. Perhaps more importantly, these high seawater temperatures limit the potential of dissolved oxygen, and therefore become an integral part of this evolutionary story. Previously, our understanding of seawater temperature during the terminal Neoproterozoic comes only from 18 O/ 16 O and 30 Si/ 28 Si ratios ascertained from a limited number of cherts. Isotopic ratio methods for assessing seawater temperatures are inherently indirect and have a wide range of oscillation. However, maximum homogenization temperatures (Th max ) of primary fluid inclusions in halite provide a direct means of assessing brine temperature, and have been shown to correlate well with average maximum air temperatures. The oldest halites date to the Neoproterozoic-lower Paleozoic (∼700-500 Ma), and Ediacaran representatives can be found in Sichuan Province, China, which do preserve primary fluid inclusions for analysis via cooling nucleation methods. We utilized halite samples from the Changning-2 well, correlative to the Dengying Formation (551-542 Ma), to provide a direct assessment of terminal Neoproterozoic seawater temperature. Our measurements indicate that seawater temperatures where these halites formed are highly similar to tropical Phanerozoic seawater temperature estimates. From compiled paleotemperature data, the decline in seawater temperatures over the course of the Proterozoic, accompanied by the reduction of seawater salinity with the sequestration of salt in massive halite deposits in the Neoproterozoic, allowed the ocean system to accumulate more dissolved oxygen, and potentially paved the way for the evolutionary innovation of complex multicellularity.
Precambrian Research, 2011
Gondwana Research, 2008
An abundance of acritarchs, dominated by Leiosphaeridia, was extracted from the Middle and Upper ... more An abundance of acritarchs, dominated by Leiosphaeridia, was extracted from the Middle and Upper Triassic cores of Ordos Basin (Northwestern China) by means of palynological maceration. Phycomata of Leiosphaeridia occurred in clusters, bunches, and single vesicular forms, occasionally with connecting macroalgal branches indicating their in-situ preservation. Apart from Proterozoic and Early Paleozoic marine Leiosphaeridia, the highly abundant leiosphaerids from the Yanchang Formation in Northwestern China likely came from a lacustrine environment, and the assemblage includes both phytoplanktonic green algae and spores of muticellular algae. TOC and δ 13 Corg in the Middle and Upper Triassic sediments of the basin show a correlation with the abundance of leiosphaerids. This correlation suggests that leiosphaerids were important biological precursors for the generation of petroleum in the main Chang 7-3 hydrocarbon source rocks.
Geobiology, 2013
The well-known debate on the nature and origin of intracellular inclusions (ICIs) in silicified m... more The well-known debate on the nature and origin of intracellular inclusions (ICIs) in silicified microfossils from the early Neoproterozoic Bitter Springs Formation has recently been revived by reports of possible fossilized nuclei in phosphatized animal embryo-like fossils from the Ediacaran Doushantuo Formation of South China. The revisitation of this discussion prompted a critical and comprehensive investigation of ICIs in some of the oldest indisputable eukaryote microfossils-the ornamented acritarchs Dictyosphaera delicata and Shuiyousphaeridium macroreticulatum from the Paleoproterozoic Ruyang Group of North Chinausing a suite of characterization approaches: scanning electron microscopy (SEM), transmission electron microscopy (TEM), and focused ion beam scanning electron microscopy (FIB-SEM). Although the Ruyang acritarchs must have had nuclei when alive, our data suggest that their ICIs represent neither fossilized nuclei nor taphonomically condensed cytoplasm. We instead propose that these ICIs likely represent biologically contracted and consolidated eukaryotic protoplasts (the combination of the nucleus, surrounding cytoplasm, and plasma membrane). As opposed to degradational contraction of prokaryotic cells within a mucoidal sheath-a model proposed to explain the Bitter Springs ICIs-our model implies that protoplast condensation in the Ruyang acritarchs was an in vivo biologically programmed response to adverse conditions in preparation for encystment. While the discovery of bona fide nuclei in Paleoproterozoic acritarchs would be a substantial landmark in our understanding of eukaryote evolution, the various processes (such as degradational and biological condensation of protoplasts) capable of producing nuclei-mimicking structures require that interpretation of ICIs as fossilized nuclei be based on comprehensive investigations.
Earth and Planetary Science Letters, 2010
Keywords: Ediacaran chert nodule pyrite SIMS sulfur isotopes fossil preservation
Astrobiology, 2007
Petrographic thin section observations suggest that the graphite particles occur within and betwe... more Petrographic thin section observations suggest that the graphite particles occur within and between quartzite clasts and are heterogeneous in origin. Using HF maceration techniques, the Wutai graphite particles were extracted for further investigation. Laser Raman spectroscopic analysis of a population of extracted graphite discs indicated that they experienced a maximum metamorphic temperature of 513 ؎ 50°C, which is consistent with the metamorphic grade of the host rock and supports their indigenicity. Scanning and transmission electron microscopy revealed that the particles bear morphological features (such as hexagonal sheets of graphite crystals) related to metamorphism and crystal growth, but a small fraction of them (graphite discs) are characterized by a circular morphology, distinct marginal concentric folds, surficial wrinkles, and complex nanostructures. Ion microprobe analysis of individual graphite discs showed that their carbon isotope compositions range from ؊7.4‰ to ؊35.9‰ V-PDB (Vienna Pee Dee Belemnite), with an average of ؊20.3‰, which is comparable to bulk analysis of extracted carbonaceous material.
2011 GSA Annual Meeting in Minneapolis, Oct 9, 2011
Exceptional preservation of non-biomineralizing tissues is, in essence, a race between degradatio... more Exceptional preservation of non-biomineralizing tissues is, in essence, a race between degradation and mineralization. These two processes are not independent from each other and, in the proper settings, can form negative feedback loops: degradation can create localized microenvironments facilitating authigenic mineralization which in turn limits degradation and promotes preservation. Such feedback loops are critical for exceptional preservation. The role of authigenic mineralization can be fulfilled by a variety of minerals ...
Geological Society of America Abstracts with Programs, Nov 6, 2012
Most of our knowledge of Neoproterozoic metazoans comes from Lagerstätten preserving fossils as m... more Most of our knowledge of Neoproterozoic metazoans comes from Lagerstätten preserving fossils as moulds and casts in siliciclastic sediments. Until recently, such Lagerstätten were believed to be unique to the Neoproterozoic, and although significant advances have been made in recent years, our incomplete understanding of this taphonomic mode remains the limiting factor in our comprehension of these fossils. A key factor in this limited understanding has been that all specimens known in this style of preservation are to some ...
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Papers by James Schiffbauer