Latha R. Menon

Haootia quadriformis n. gen., n. sp., interpreted as a muscular cnidarian impression from the Late Ediacaran period (approx. 560 Ma)

Muscle tissue is a fundamentally eumetazoan attribute. The oldest evidence for fossilized muscular tissue before the Early Cambrian has hitherto remained moot, being reliant upon indirect evidence in the form of Late Ediacaran ichnofossils. We here report a candidate muscle-bearing organism, Haootia quadriformis n. gen., n. sp., from approximately 560 Ma strata in Newfoundland, Canada. This taxon exhibits sediment moulds of twisted, superimposed fibrous bundles arranged quadrilaterally, extending into four prominent bifurcating corner branches. Haootia is distinct from all previously published contemporaneous Ediacaran macrofossils in its symmetrically fibrous, rather than frondose, architecture. Its bundled fibres, morphology, and taphonomy compare well with the muscle fibres of fossil and extant Cnidaria, particularly the benthic Staurozoa. Haootia quadriformis thus potentially provides the earliest body fossil evidence for both metazoan musculature, and for Eumetazoa, in the geological record.

Evidence for Cnidaria-like behavior in ca. 560 Ma Ediacaran Aspidella

The first appearance of animals in the geological record is a matter of continuing debate: how deep were the roots of the Cambrian explosion? Molecular clock estimates indicate that the deepest divergences of the Metazoa had occurred by the Ediacaran Period (635–541 Ma), yet evidence of animal activity from well below the Ediacaran-Cambrian boundary has been rare and often questionable. Meanwhile, the Ediacaran macrobiota has remained enigmatic, as emphasized by recent controversial claims that South Australia Ediacaran forms were not marine animals at all, but land-based lichens and microbial colonies. Here we report evidence for animal-like behavior in a submerged setting in a key Ediacaran form, Aspidella terranovica Billings 1872, a discoidal fossil from the ca. 560 Ma Fermeuse Formation of Newfoundland (Canada). We describe sedimentary fabrics indicating progressive vertical movement of an organism through sediment in response to an aggrading sediment-water interface. Such equilibrium traces are familiar from the Phanerozoic and are observed in partially buried marine animals such as tube anemones today. Furthermore, horizontal trails closely comparable to trails previously described from ∼565 m.y. old Mistaken Point (Newfoundland) are now linked to Aspidella . Our findings constitute evidence of both vertical and horizontal movement in a key Ediacaran taxon, consistent with an animal of cnidarian grade. Moreover, because Aspidella is also reported from the Rawnsley Quartzite of South Australia, our evidence conflicts with the proposed radical interpretation of that Ediacaran fossil assemblage. We demonstrate that at least some Ediacaran forms were probably early animals, and that they lived underwater.

The oldest evidence of bioturbation on Earth: COMMENT

Here we question the conclusions of Rogov et al. (2012), who claim to describe “the oldest evidence of bioturbation on Earth” in the form of meniscate backfi lled burrows and escape traces from late Ediacaran car- bonates of the Siberian Khatyspyt Formation. Because trace fossils can constrain early Metazoan origins, and are used to defi ne the base of the Cambrian Period (Brasier et al., 1994), such a signifi cant claim requires jus- tifi cation by careful interpretation of the material, and critical analysis, both of which appear wanting here. Although we agree that multiple biological and ecological revolutions took place during the late Ediacaran Period, we question whether those events can be tied to these problematic fossils.

The dynamic influence of microbial mats on sediments: fluid escape and pseudofossil formation in the Ediacaran Longmyndian Supergroup, UK

Microbial mats are thought to have been widespread in marine settings before the advent of bioturbation, and the range of their influence on sediments is gradually becoming recognized. We propose that mat sealing can dynamically affect porewater conditions, and allow the build-up of overpressure that can drive dewatering and degassing to produce a suite of atypical fluid-escape features. Finely bedded silty and sandy laminae from the c. 560 Ma Burway Formation of the Longmyndian Supergroup, Shropshire, England, reveal evidence for sediment injection, including disrupted bedding, clastic injections, sill-like features and sediment volcanoes at sub-millimetre scale. These features are associated with crinkly laminae diagnostic of microbial matgrounds. Matground-associated sediment injection can explain the formation of several types of enigmatic discoidal impressions, common in rocks of this age, which have previously been attributed to the Ediacaran macrobiota. Serial grinding of Longmyndian forms previously described as Medusinites aff. asteroides and Beltanelliformis demonstrates that such discoidal features can be fully explained by fluid escape and associated load structures. Our observations emphasize the non-actualistic nature of shallow-marine Ediacaran sediments. Matground-associated sediment injection features provide a new insight into the interpretation of Proterozoic rocks and the biogenicity of their enigmatic discoidal markings. Supplementary materials: A document containing further images of fluid escape and loading features observed in the upper Burway Formation at Ashes Hollow, together with an annotated diagram of features appearing in one typical vertical cross-section, is available at www.geolsoc.org.uk/SUP18870.

Osmotrophic Biofilms: From Modern to Ancient

We here explore the potential of nonphotosynthetic microbes as significant players in the formation and preservation of structures such as microbial mats and soil-like networks. In particular, we focus on organisms such as actinobacteria and fungi, known to feed by osmotic absorption of preformed organic compounds, which we collectively refer to as “osmotrophs” here. We show that they have a fossil record that may be traced far back into the Proterozoic in a range of sedimentary environments.

The arrangement of possible muscle fibres in the Ediacaran taxon Haootia quadriformis

Haootia quadriformis from Newfoundland, Canada, is one of the most unusual impressions of a soft-bodied macro-organism yet described from the late Ediacaran Period. Interpreted as a metazoan of cnidarian grade [[1][1]], the body impression of H. quadriformis possesses features interpreted as fibrous

‘Intrites’ from the Ediacaran Longmyndian Supergroup, UK: a new form of microbially-induced sedimentary structure (MISS)

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.

Understanding ancient life: how Martin Brasier changed the way we think about the fossil record

Abstract Crucial to our understanding of life on Earth is the ability to judge the validity of claims of very ancient ‘fossils’. Martin Brasiers 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.

A Tribute to Martin D. Brasier: Palaeobiologist and Astrobiologist (April 12, 1947-December 16, 2014).

The late Martin Brasier, emeritus professor of palaeobiology at the University of Oxford, was perhaps best known among the astrobiology community for his research on the Archean biosphere and for testing the oldest microfossil evidence in the rock record. But this would overlook the broad-ranging and multifaceted scientist that Martin was, with research interests spanning the entire history of life on Earth, which we have attempted to capture in this tribute. Martin was at the center of many important paleobiological debates over the last 40 years and contributed to our understanding of Earth’s biosphere at key transitions in Earth’s history. He was a keen advocate of the field of astrobiology, bringing his extensive geological and paleontological experience to bear. In this tribute we have compiled the reflections of several former students, international collaborators, and academic colleagues with the aim of describing Martin’s broad-ranging and far-reaching contributions. First we present a brief overview of Martin’s academic research, which is by no means intended to be exhaustive, before reporting the personal accounts of several scientists who had the privilege of working and/or interacting with Martin during his extensive career. Martin undertook a PhD at University College London on the ecology and microhabitats of modern benthic foraminifera, algae, and sea-grass communities of the Caribbean island of Barbuda. Martin was engaged as ship’s scientist aboard the Royal Navy ship HMS Fox and Fawn, an opportunity which he likened to Darwin’s position on the HMS Beagle, and during that time he undertook much fundamental research. Martin was both a conventional and unconventional micropaleontologist, as described in the contribution by Owen Green below. In the 1970s Martin undertook mathematical studies of foraminiferid morphospace to investigate the evolution of foraminifera photosymbioses through time. The concept of morphospace analysis was an approach that Martin would later return to in other areas of his research, for example, to test the biogenicity of carbonaceous microfossils, also to investigate the evolution and growth of the Ediacaran biota. In the 1980s while based at the University of Hull, Martin worked on Lower Cambrian reef systems, particularly on several expeditions to Mongolia, one important outcome of which was to reveal the sponge-like biology of archaeocyathids. At this time Martin was also undertaking an ecological and taphonomic assessment of the Cambrian diversification of skeletal fossils. Throughout his career Martin was an advocate of the high-resolution analysis of fossils in their sedimentological and geological context (see, e.g., the contribution by Duncan McIlroy below, reflecting on work to characterize the Ediacaran and Cambrian evolutionary radiations). In 1988 Martin moved to the Department of Earth Sciences at the University of Oxford and took a leading role in the International Geological Correlation Programme (IGCP), particularly in their work to formally define the Cambrian time period, and in the selection of the global stratotype section in Newfoundland. Martin worked extensively on Proterozoic geobiological evolution; for instance, he coined the phrase ‘‘the Boring Billion’’ to refer to the apparent evolutionary quiescence of the Mesoproterozoic. In Australia he worked with John Lindsay,

Martin Brasier's contribution to the palaeobiology of the Ediacaran–Cambrian transition

Abstract Martin Brasiers 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 Martins main contributions to this area of research and assess the impact of his findings on the development of this field.