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Research Interests: Evolutionary Biology, Geology, Paleontology, Biology, Ecology, and 4 moreDiagenesis, Population, Juvenile, and Taxon
The Neoproterozoic Ediacara biota at Mistaken Point contains the oldest diverse Ediacaran assemblages and is one of the few known deepwater localities, yet the biota is dominated by endemic forms, nearly all of which remain undescribed.... more
The Neoproterozoic Ediacara biota at Mistaken Point contains the oldest diverse Ediacaran assemblages and is one of the few known deepwater localities, yet the biota is dominated by endemic forms, nearly all of which remain undescribed. Thectardis avalonensis new genus and species, one of these endemic forms, is a cm-scale triangular fossil with a raised rim and a featureless-to-faintly-segmented central depression. More than 200 specimens occur on two bedding plane surfaces: the 565 Ma E surface and the 575 Ma Pigeon Cove surface, nearly 2,000 m lower in the succession. Morphological and taphonomic data suggest that the organism was an elongate cone that may have lived as a suspension-feeding “mat sticker” with its pointed base inserted into the microbially bound sediment. If true, Thectardis n. gen. would be the tallest-known mat sticker, reaching a maximum height of over 15 cm. Specimens display little ontogenetic change in length:width ratio, suggesting that Thectardis grew uniformly by incremental addition of material to its distal end. Morphological differences between specimens at two well-separated stratigraphic levels may have resulted from evolutionary or ecophenotypic variation.
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Research Interests: Evolutionary Biology, Geology, Paleontology, Biology, Ecology, and 3 morePalaeontology, Anatomy, and Trilobite
Suspension feeding is a key ecological strategy in modern oceans that provides a link between pelagic and benthic systems. Establishing when suspension feeding first became widespread is thus a crucial research area in ecology and... more
Suspension feeding is a key ecological strategy in modern oceans that provides a link between pelagic and benthic systems. Establishing when suspension feeding first became widespread is thus a crucial research area in ecology and evolution, with implications for understanding the origins of the modern marine biosphere. Here, we use three-dimensional modelling and computational fluid dynamics to establish the feeding mode of the enigmatic Ediacaran pentaradial eukaryote Arkarua. Through comparisons with two Cambrian echinoderms, Cambraster and Stromatocystites, we show that flow patterns around Arkarua strongly support its interpretation as a passive suspension feeder. Arkarua is added to the growing number of Ediacaran benthic suspension feeders, suggesting that the energy link between pelagic and benthic ecosystems was likely expanding in the White Sea assemblage (~ 558–550 Ma). The advent of widespread suspension feeding could therefore have played an important role in the subseq...
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The lower Cambrian (Cambrian Series 2, Stage 4) Emu Bay Shale Konservat-Lagerstäette from the north coast of Kangaroo Island, South Australia, is by far the best preserved and taxonomically diverse Burgess Shale-type fauna in Australia.... more
The lower Cambrian (Cambrian Series 2, Stage 4) Emu Bay Shale Konservat-Lagerstäette from the north coast of Kangaroo Island, South Australia, is by far the best preserved and taxonomically diverse Burgess Shale-type fauna in Australia. It occurs mainly within dark grey to black laminated mudstone in the basal 10 metres of the Emu Bay Shale, the base of which is a sequence boundary. Interbedded structureless fine sandstone horizons up to 20 cm thick are interpreted as mass flow or storm deposits; there is evidence of syndepositional faulting and rapid deposition. The sediments were derived from an uplifted Precambrian land mass a short distance to the northwest. There is no sign of bioturbation thus suggesting anoxic conditions immediately below the sediment-water boundary. The abundance of fossils and trace element geochemical data indicate that the overlying water column was oxic with a sharp redox boundary at the sediment-water interface that was possibly maintained by mat-forming cyanophytes thus suggesting clear, relatively shallow water. There were at least two preservational pathways: pyritization and phosphatization. The trilobites Estaingia bilobata and Redlichia takooensis (up to 25 cm long) dominate the fossil assemblage of over 50 taxa. Other trilobites are rare and represent vagrants. Recent work includes descriptions of the bivalved arthropods Isoxys and Tuzoia, two new nektaspid arthropods (Emucaris, Kangacaris), a new leanchoiliid megacheiran arthropod (Oestokerkus) and a new palaeoscolecid. Other fossils include Myoscolex, demosponges, a vetulicolian, an odontogriphid, hyoliths, brachiopods, numerous problematic taxa, and well preserved eyes of an unknown arthropod plus those of Anomalocaris.1 page(s
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Research Interests: Geology and Phanerozoic
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Dickinsonia is one of the oldest macroscopic metazoans in the fossil record. Determining the biological characters of this extinct taxon is critical to our understanding of the early evolution of life. Preservation of abundant specimens... more
Dickinsonia is one of the oldest macroscopic metazoans in the fossil record. Determining the biological characters of this extinct taxon is critical to our understanding of the early evolution of life. Preservation of abundant specimens from the Ediacara Member (Rawnsley Quartzite), South Australia, in a variety of taphonomic states allows the unparalleled opportunity to compare the biomechanical responses of Dickinsonia tissue to various forces with those typical of modern organisms. Dickinsonia are found as lifted, transported, folded, rolled, ripped, and expanded or contracted individuals, while maintaining diagnostic morphology. This suite of characters indicates that Dickinsonia was composed of material that was flexible, difficult to rip, and capable of elastic and plastic deformation. While none of these traits are diagnostic of a single biomaterial component, we find many similarities with modern biopolymers, particularly collagen, keratin, and elastin. Maintenance of significant relief following complete tearing suggests that Dickinsonia was composed of relatively thick tissues, signifying higher oxygen requirements than previously hypothesized. The ability to be transported and still be preserved as recognizable fossils is unique amongst the Ediacara Biota and demonstrates that Dickinsonia was a taphonomic elite. Combined with discovery in multiple environmental settings, this indicates that the absence of Dickinsonia represents the likely extinction of this organism prior to the Nama assemblage, possibly due to a decrease in the global availability of oxygen in the latest Ediacaran.
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Significance The transition from simple, microscopic forms to the abundance of complex animal life that exists today is recorded within soft-bodied fossils of the Ediacara Biota (571 to 539 Ma). Perhaps most critically is the first... more
Significance The transition from simple, microscopic forms to the abundance of complex animal life that exists today is recorded within soft-bodied fossils of the Ediacara Biota (571 to 539 Ma). Perhaps most critically is the first appearance of bilaterians—animals with two openings and a through-gut—during this interval. Current understanding of the fossil record limits definitive evidence for Ediacaran bilaterians to trace fossils and enigmatic body fossils. Here, we describe the fossil Ikaria wariootia, one of the oldest bilaterians identified from South Australia. This organism is consistent with predictions based on modern animal phylogenetics that the last ancestor of all bilaterians was simple and small and represents a rare link between the Ediacaran and the subsequent record of animal life.
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The evolutionary trajectory of early complex life on Earth is interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota, which appeared and evolved during a time of dynamic biogeochemical and environmental... more
The evolutionary trajectory of early complex life on Earth is interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota, which appeared and evolved during a time of dynamic biogeochemical and environmental fluctuation in the global ocean. The Ediacara Biota is historically divided into three successive Assemblages—the Avalon, the White Sea, and the Nama—which are marked by the appearance of novel biological traits and ecological strategies. In particular, the younger White Sea and Nama Assemblages record a “second wave” of ecological innovations, which included not only the development of uniquely Ediacaran body plans and ecologies, such as matground adaptations, but also the dual emergence of bilaterian-grade animals and Phanerozoic-style ecological innovations, including spatial heterogeneity, complex reproductive strategies, ecospace utilization, motility, and substrate competition. The late Ediacaran was an evolutionarily dynamic time characterized by strong environmental control over the distribution of taxa in time and space.
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Research Interests: Astrobiology and Planet
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Mobility represents a key innovation in the evolution of complex animal life. The ability to move allows for the exploration of new food sources, escapes from unfavorable environmental conditions, enhanced ability to exchange genetic... more
Mobility represents a key innovation in the evolution of complex animal life. The ability to move allows for the exploration of new food sources, escapes from unfavorable environmental conditions, enhanced ability to exchange genetic material, and is one of the major reasons for the diversity and success of animal life today. The oldest widely accepted trace fossils of animal mobility are found in Ediacaran‐aged rocks (635–539 Ma). The earliest definitive evidence for movement associated with exploitation of resources for feeding occurs in the White Sea assemblage of the Ediacara Biota—macroscopic, soft‐bodied fossils of Ediacaran age. Here, we evaluate potential support for mobility in dickinsoniomorphs, presenting new data regarding abundant Dickinsonia and associated trace fossils from the Ediacara Member, South Australia. Results quantitatively demonstrate that Dickinsonia was capable of mobility on relatively short, ecological timescales. This organism was bilaterally symmetric...
Research Interests: Geology, Geochemistry, Geobiology, Biology, Ecology, and 5 moreMedicine, Organism, Trace Fossil, Biota, and Taxon
Research Interests: Palaeogeography, Geology, Paleontology, Oil Shale, Gondwana, and 3 morePaleozoic, Lagerstätte, and Bay
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Ediacaran trace fossils are becoming an increasingly less common component of the total Precambrian fossil record as structures previously interpreted as trace fossils are reinterpreted as body fossils by utilizing qualitative criteria.... more
Ediacaran trace fossils are becoming an increasingly less common component of the total Precambrian fossil record as structures previously interpreted as trace fossils are reinterpreted as body fossils by utilizing qualitative criteria. Two morphotypes, Form E and Form F of Glaessner (1969), interpreted as trace fossils from the Ediacara Member of the Rawnsley Quartzite in South Australia are shown here to be body fossils of a single, previously unidentified tubular constructional morphology formally described herein as Somatohelix sinuosus n. gen. n. sp. S. sinuosus is 2-7 mm wide and 3-14 cm long and is preserved as sinusoidal casts and molds on the base of beds. Well-preserved examples of this fossil preserve distinct body fossil traits such as folding, current alignment, and potential attachment to holdfasts. Nearly 200 specimens of this fossil have been documented from reconstructed bedding surfaces within the Ediacara Member. When viewed in isolated hand sample, many of these specimens resemble ichnofossils. However, the ability to view large quantities of reassembled and successive bedding surfaces within specific outcrops of the Ediacara Member provides a new perspective, revealing that isolated specimens of rectilinear grooves on bed bases are not trace fossils but are poorly preserved specimens of S. sinuosus. Variation in the quality and style of preservation of S. sinuosus on a single surface and the few distinct characteristics preserved within this relatively indistinct fossil also provides the necessary data required to define a taphonomic gradient for this fossil. Armed with this information, structures which have been problematic in the past can now be confidently identified as S. sinuosus based on morphological criteria. This suggests that the original organism that produced this fossil was a widespread and abundant component of the Ediacaran ecosystem.
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We report the preservation of the eight-armed Ediacara fossil Eoandromeda octobrachiata as carbonaceous compressions in the Doushantuo black shale of south China and as casts and molds in the Rawnsley Quartzite in South Australia. The... more
We report the preservation of the eight-armed Ediacara fossil Eoandromeda octobrachiata as carbonaceous compressions in the Doushantuo black shale of south China and as casts and molds in the Rawnsley Quartzite in South Australia. The contrasting preservational styles ...
Research Interests: Earth Sciences, Geology, China, Icon, South Australia, and 4 moreSouth China, Citation, ICON, and Black Shale
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Research Interests: Geology and Paleoecology
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Constraining patterns of growth using directly observable and quantifiable characteristics can reveal a wealth of information regarding the biology of the Ediacara Biota – the oldest macroscopic, complex community forming organisms in the... more
Constraining patterns of growth using directly observable and quantifiable characteristics can reveal a wealth of information regarding the biology of the Ediacara Biota – the oldest macroscopic, complex community forming organisms in the fossil record. However, these rely on individuals captured at an instant in time at various growth stages, and so different interpretations can be derived from the same material. Here we leverage newly discovered and well-preserved Dickinsonia costata Sprigg 1947 from South Australia, combined with hundreds of previously described specimens, to test competing hypotheses for the location of module addition. We find considerable variation in the relationship between the total number of modules and body size that cannot be explained solely by expansion and contraction of individuals. Patterns derived assuming new modules differentiated at the anterior result in numerous examples where the oldest module(s) must decrease in size with overall growth, potentially falsifying this hypothesis. Observed polarity as well as the consistent posterior location of defects and indentations support module formation at this end in D. costata. Regardless, changes in repeated units with growth share similarities with those regulated by morphogen gradients in metazoans today, suggesting that these genetic pathways were operating in Ediacaran animals.
Research Interests: Evolutionary Biology, Paleobiology, Geology, Biology, Ecology, and 3 moreMedicine, Biota, and Modular Design
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The Ediacara Biota represents a turning point in the evolution of life on Earth, signifying the transition from single celled organisms to complex, community-forming macrobiota. The exceptional fossil record of the soft-bodied Ediacara... more
The Ediacara Biota represents a turning point in the evolution of life on Earth, signifying the transition from single celled organisms to complex, community-forming macrobiota. The exceptional fossil record of the soft-bodied Ediacara Biota provides critical insight into the nature of this transition and into ecosystem dynamics leading up to the so-called “Cambrian Explosion”. However, the preservation of non-biomineralizing organisms in a diversity of lithologies goes hand-in-hand with considerable taphonomic complexity that often shrouds true paleoecological and paleobiological signatures. We address the nature of this taphonomic complexity within the fossiliferous sandstones of the Ediacara Member in South Australia. Utilizing the most fossiliferous outcropping of the Ediacara Member, located at the Nilpena Station National Heritage Ediacara Fossil Site, we conduct a focused, taxon-level biostratinomic characterization of the tubular organism Funisia dorothea. Funisia is the mos...
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The Precambrian Ediacara Biota—Earth's earliest fossil record of communities of macroscopic, multicellular organisms—provides critical insights into the emergence of complex life on our planet. Excavation and reconstruction of nearly... more
The Precambrian Ediacara Biota—Earth's earliest fossil record of communities of macroscopic, multicellular organisms—provides critical insights into the emergence of complex life on our planet. Excavation and reconstruction of nearly 300 m 2 of fossiliferous bedding planes in the Ediacara Member of the Rawnsley Quartzite, at the National Heritage Ediacara fossil site Nilpena in South Australia, have permitted detailed study of the sedimentology, taphonomy and palaeoecology of Ediacara fossil assemblages. Characterization of Ediacara macrofossils and textured organic surfaces at the scale of facies, bedding planes and individual specimens has yielded unprecedented insight into the manner in which the palaeoenvironmental settings inhabited by Ediacara communities—particularly hydrodynamic conditions—influenced the aut- and synecology of Ediacara organisms, as well as the morphology and assemblage composition of Ediacara fossils. Here, we describe the manner in which environmental ...