Abstract The ichnology between marine and non-marine environments is a key field of work concerning the understanding of the variation of environmental parameters in inland-to-offshore transitional environments. In order to understand the geological and palaeobiological processes at these locations, this Special Publication attempts to discuss records in shallow-marine and transitional environments throughout the Phanerozoic, including topics such as ichnotaxonomy, ichnofacies analysis, ichnofabric analysis for records from both shallow-marine and transitional environments, and neoichnological aspects. The volume includes 14 papers in total: one focused on aspects of neoichnology in rock iguanas in coastal settings, nine concerning various shallow-marine palaeoenvironment topics and four addressing issues about dinosaur tracks in transitional environments.

Abstract Understanding early life has been one of the hottest topics in palaeobiology for many years, attracting some of the finest palaeontological minds. Three of the most fundamental innovations in the history of life were the appearance of the first cells, the evolution of multi-cellularity and the evolution of animals. The MOFAOTYOF principle (my oldest fossils are older than your oldest fossils) commonly clouds discussions around the oldest fossil evidence, requiring a rigorous and critical approach to determining which fossils are reliable and should form the basis of our understanding of early life. In addition, evidence for early fossils must be considered within their spatial context; we need to understand the conditions under which they were preserved and how they were preserved. This book summarizes recent progress in the fields of: (1) the cellular preservation of early microbial life; and (2) the early evolution of macroscopic animal life, including the Ediacaran biota. Deciphering the evidence for early life requires some degree of exceptional preservation, employment of state-of-the-art techniques and also an understanding gleaned from Phanerozoic lagerstätte and modern analogues. This integrated approach to understanding fossils, combined with adoption of the null hypothesis that all putative traces of life are abiotic until proved otherwise, characterized the work of Martin Brasier, as is well demonstrated by the papers in this book. Supplementary material: A chronological listing of all Martin Brasier’s publications is available at https://doi.org/10.6084/m9.figshare.c.3727696 Gold Open Access : This article is published under the terms of the CC-BY 3.0 license.

Abstract Crucial to our understanding of life on Earth is the ability to judge the validity of claims of very ancient ‘fossils’. Martin Brasier’s most important contribution to this debate was to establish a framework within which to discuss claims of the ‘oldest’ life. In particular, he made it clear that the burden of proof must fall on those making the claim of ancient life, not those refuting it. This led to his formulation of the concept of the continuum of morphologies produced by life and non-life and the considerable challenges of differentiating biogenesis from abiogenesis. Martin Brasier developed a set of criteria for distinguishing life from non-life and extended the use of many new high-resolution analytical techniques to palaeontological research. He was also renowned for his work on the Cambrian explosion and the origin of animals. Although he had spent much of his early career working on the geological context of these events, it was not until he returned to studying the Ediacaran and Cambrian periods in his later years that he began to apply this null hypothesis way of thinking to these other major transitions in the history of life. This led to him becoming involved in the development of a series of nested null hypotheses, his ‘cone of contention’, to analyse enigmatic fossils more generally. In short, Martin Brasier taught us how to formulate biological hypotheses in deep time, established the rules for how those hypotheses should be tested and championed a host of novel analytical techniques to gather the data required. As a consequence, future discussions of enigmatic specimens and very old fossils will be greatly enriched by his contributions.

Abstract Martin Brasier’s work spanned almost the entire geological column, but the origin of animals and the nature of the Cambrian explosion were areas of particular interest to him. Martin adopted a holistic approach to the study of these topics that considered the interplay between multiple geological and biological phenomena and he sought to interpret the fossil record within the broad context of geological, biogeochemical and ecological changes in the Earth system. Here we summarize Martin’s main contributions to this area of research and assess the impact of his findings on the development of this field.

Abstract The large, enigmatic members of the Ediacaran biota have received much attention regarding their possible affinities and mode of life. Fossil evidence reveals that many Ediacaran animals, such as the rangeomorphs, were characterized by extensive surface areas, lived in close association with the seafloor and were non-motile. We argue for the presence of a simple, diploblastic body plan in these early animals and discuss the means by which they probably derived nutrients from chemosynthetic bacteria thriving at the sediment–water interface. We consider that the large surface area of some Ediacaran organisms in the Avalonian biota may have been an adaptation for maximizing a phagocytotic or chemosymbiotic surface. Ediacaran animals probably increased the availability of oxygen along their ventral surface either by diffusion or ciliary pumping. This increased supply of oxygen to the sediment is inferred to have simultaneously increased the productivity of their food source (chemosynthetic bacteria) and restricted the build-up of toxic sulphides in the pore waters below their bodies. This is an example of a very simple form of ecosystem engineering. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license .

Abstract Fossil assemblages from Newfoundland’s Avalon Peninsula preserve diverse examples of the enigmatic Ediacaran macrobiota, offering some of the earliest evidence for large and complex multicellular life. These fossils are exposed on extensive coastal bedding planes in extraordinary abundances, permitting palaeoecological studies based on census data from spatially extensive palaeocommunities. Such studies have been used to constrain the reproductive strategy and phylogenetic placement of Ediacaran organisms. Geological mapping and stratigraphic correlation in the Mistaken Point Ecological Reserve reveal that some fossil-bearing surfaces can be tracked over distances of several kilometres. These laterally extensive surfaces reveal that the modern processes by which the sediment overlying a fossil surface is removed may impose important controls on the observed composition of fossil assemblages. Weathering and erosion – along with factors associated with tectonics, metamorphism and discovery – are here grouped as ‘post-fossilization processes’ and introduce biases that are often not explicitly accounted for in palaeoecological studies. Specifically, post-fossilization processes may differentially influence the preservational fidelity of individual specimens on a given surface and generate features that could be mistaken for original morphological characters. We therefore recommend that post-fossilization processes must be considered when undertaking palaeoecological studies in Ediacaran successions in Newfoundland and, potentially, elsewhere. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license .

Abstract Simple discoidal impressions are the only evidence of complex life in some Ediacaran and older rocks, but their interpretation is notoriously difficult. We reassessed a puzzling discoidal form from the c. 560 Ma upper Burway Formation of the Ediacaran Longmyndian Supergroup, Shropshire, UK. The structures, previously described as Intrites punctatus Fedonkin, are found on both the bed tops and soles. They vary in morphology from mounds with central depressions to incomplete rings and pairs of short ridges. Examination of the purported Intrites documented from the Longmyndian in cross-section revealed a torus-shaped structure bounded by microbial mat layers and commonly containing white laminae. We interpret the ‘Longmyndian Intrites ’ as a product of microbial trapping, sediment binding and authigenic clay mineral and carbonate precipitation on the flanks of small sediment volcanoes. Subsidence of the ring-like structure into muddy sediments resulted in a torus-shaped microstromatolite. Preferential stromatolitic growth parallel to the prevailing current produced the observed partial rings or parallel ridges and explains their preferential orientation as current alignment. This interpretation of ‘Longmyndian Intrites ’ expands the known variety of microbially-induced sedimentary structures (MISS) and emphasizes the importance of considering microbially-induced structures and abiological processes when interpreting discoidal impressions in ancient rocks. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license .

Abstract The rock record attests that sediments have cracked at or below the sediment–water interface in strictly subaqueous settings throughout Earth history. In recent decades, a number of hypotheses have been advanced to explain this phenomenon, but these are widely regarded as being mutually exclusive and there is little consensus about which model is correct. In this paper, we first review the geometries, lithologies and range of facies in which subaqueous sedimentary cracks occur in the geological record, with particular attention to cracks in carbonates. We then evaluate current models for subaqueous cracking, emphasizing that different models may be correct with respect to different sets of cracks, but that cracking is generally a two-step process involving sediment stabilization prior to disruption. We also present the results of some simple new experiments designed to test the dominant models of crack formation. These results demonstrate for the first time that microbial mats can produce thin, shallow cracks at the sediment–water interface. We conclude that the presence of cracks in marine, brackish and lacustrine rocks should not be used uncritically to infer fluctuations in salinity in the depositional environment. Supplementary material: A video showing a micro-CT scan of a hand-sample from the Monteville Formation, South Africa is available at https://doi.org/10.6084/m9.figshare.c.3580673 Gold Open Access: This article is published under the terms of the CC-BY 3.0 license .

Abstract The Ediacaran to Cambrian transition of the Digermul Peninsula consists of an ichnologically rich, thick, conformable, shallow marine siliciclastic succession that crosses the Neoproterozoic–Cambrian boundary. The Tanafjord section has been independently dated by published palynological and new body fossil discoveries. As is also observed at the current Global Stratotype Section and Point (GSSP) for the Ediacaran–Cambrian boundary at Fortune Head in Newfoundland, Canada, there is a marked increase in burrow size and inferred behavioural diversity around the inferred boundary level at a surface without a significant hiatus. The diversity of this trace fossil assemblage presents an opportunity to compare the ichnological first appearance datums between the GSSP and another sedimentologically similar, but palaeogeographically remote, succession. We found that the first appearance datums of taxa in Finnmark broadly support the definition and stratigraphic extents of the Harlaniella podolica , Treptichnus pedum, Rusophycus avalonensis and Cruziana tenella zones. Our work shows that there is a marked increase in ichnodiversity in the lowermost Fortunian, mostly in the form of shallow tier traces. The main post-Fortunian ichnological innovation is the evolution of bulk sediment deposit feeding that is first evidenced by spreiten burrows at around the base of Cambrian Stage 2 in both the GSSP and in the Tanafjord section. Supplementary material: Additional images of trace fossils from the studied section are available at https://doi.org/10.6084/m9.figshare.c.3462561 Gold Open Access: This article is published under the terms of the CC-BY 3.0 license .

Abstract By applying modern biological criteria to trace fossil types and assessing burrow morphology, complexity, depth, potential burrow function and the likelihood of bioirrigation, we assign ecosystem engineering impact (EEI) values to the key ichnotaxa in the lowermost Cambrian (Fortunian). Surface traces such as Monomorphichnus have minimal impact on sediment properties and have very low EEI values; quasi-infaunal traces of organisms that were surficial modifiers or biodiffusors, such as Planolites , have moderate EEI values; and deeper infaunal, gallery biodiffusive or upward-conveying/downward-conveying traces, such as Teichichnus and Gyrolithes , have the highest EEI values. The key Cambrian ichnotaxon Treptichnus pedum has a moderate to high EEI value, depending on its functional interpretation. Most of the major functional groups of modern bioturbators are found to have evolved during the earliest Cambrian, including burrow types that are highly likely to have been bioirrigated. In fine-grained (or microbially bound) sedimentary environments, trace-makers of bioirrigated burrows would have had a particularly significant impact, generating advective fluid flow within the sediment for the first time, in marked contrast with the otherwise diffusive porewater systems of the Proterozoic. This innovation is likely to have created significant ecospace and engineered fundamentally new infaunal environments for macrobiotic and microbiotic organisms alike. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license .