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Abstract The “second wave” of Ediacaran evolution (∼558–548 Ma) was characterized by the appearance of macroscopic organisms in shallow marine settings, where they formed communities with high morphological and ecological diversity, including new and more complex modes of life. Based on analogy with modern marine ecosystems, these early shallow water communities could have substantially modified local hydrodynamic conditions and influenced resource availability, but we know very little about how they interacted with their fluid environment at larger spatial scales. Here, we use computational fluid dynamics to investigate the hydrodynamics of different shallow marine Ediacaran communities based on fossil surfaces from Russia and South Australia. Our results reveal considerable hydrodynamic variability among these communities, ranging from unobstructed flow, to enhanced mixing, to very low in-canopy flow. This variability represents a noticeable shift from the more conserved hydrodynamic conditions reconstructed for older Ediacaran communities from deep water settings. The variation in how shallow marine Ediacaran communities affected local hydrodynamics could have given rise to notable differences in the distribution of crucial water-borne resources such as organic carbon and oxygen. We therefore hypothesize that increasing variability in community hydrodynamics was an important source of habitat heterogeneity during the late Ediacaran. On long timescales, this heterogeneity may have helped sculpt ecological opportunity, fostering the radiation of animals. 

Abstract Tribrachidium heraldicumis an Ediacaran body fossil characterized by triradial symmetry. Previous work has suggested that the anatomy ofTribrachidiumwas conducive to passive suspension feeding; however, these analyses used an inaccurate model and a relatively simple set of simulations. Using computational fluid dynamics, we explore the functional morphology ofTribrachidiumin unprecedented detail by gauging how the presence or absence of distinctive anatomical features (e.g., apical pits and arms) affects flow patterns. Additionally, we map particle pathways, quantify deposition rates at proposed feeding sites, and assess gregarious feeding habits to more fully reconstruct the lifestyle of this enigmatic taxon. Our results provide strong support for interpretingTribrachidiumas a macroscopic suspension feeder, with the apical pits representing loci of particle collection (and possibly ingestion) and the triradial arms representing morphological adaptations for interrupting flow and inducing settling. More speculatively, we suggest that the radial grooves may represent ciliated pathways through which food particles accumulating in the wake of the organism were transported toward the apical pits. Finally, our results allow us to generate new functional hypotheses for other Ediacaran taxa with a triradial body plan. This work refines our understanding of the appearance of suspension feeding in shallow-water paleoenvironments, with implications for the radiation of Metazoa across the Ediacaran/Cambrian boundary. 

Abstract The evolutionary rise of powerful new ecosystem engineering impacts is thought to have played an important role in driving waves of biospheric change across the Ediacaran–Cambrian transition (ECT;c. 574–538 Ma). Among the most heavily cited of these is bioturbation (organism‐driven sediment disturbance) as these activities have been shown to have critical downstream geobiological impacts. In this regard priapulid worms are crucial; trace fossils thought to have been left by priapulan‐grade animals are now recognized as appearing shortly before the base of the Cambrian and represent some of the earliest examples of bed‐penetrative bioturbation. Understanding the ecosystem engineering impacts of priapulids may thus be key to reconstructing drivers of the ECT. However, priapulids are rare in modern benthic ecosystems, and thus comparatively little is known about the behaviours and impacts associated with their burrowing. Here, we present the early results of neoichnological experiments focused on understanding the ecosystem engineering impacts of priapulid worms. We observe for the first time a variety of new burrowing behaviours (including the formation of linked burrow networks and long in‐burrow residence times) hinting at larger ecosystem engineering impacts in this group than previously thought. Finally, we identify means by which these results may contribute to our understanding of tracemakers across the ECT, and the role they may have had in shaping the latest Ediacaran and earliest Cambrian biosphere. 

The Nama Group (Kalahari Craton) is an archetypal stratigraphic record of the Ediacaran–Cambrian transition. The upper Schwarzrand Subgroup preserves key biostratigraphic markers of this interval, including erniettomorphs, cloudinomorphs, and trace fossils, yet has a complex stratigraphic architecture due to deposition in a foreland basin. Here, we describe the stratigraphy of the upper Schwarzrand Subgroup of the Nama Basin, and collate sedimentologic, geochronologic, carbon isotope chemostratigraphic, and biostratigraphic data. We argue that strata previously identified as the Nomtsas Formation in the Witputs Subbasin are lithostratigraphically and tectonostratigraphically distinct from those in the type area (Farm Nomtsas) in the Zaris Subbasin. Therefore, we introduce the Swartkloofberg Formation as a new name for the terminal Schwarzrand Subgroup in the Witputs Subbasin. While carbonates of the underlying Urusis Formation were deposited within shallow marine environments, the Swartkloofberg Formation records a transition to dominantly siliciclastic deposition, mostly below fair-weather wave base, and with extensive evidence of slope instability. High-relief stromatolite reefs formed diachronously at different localities within both the Urusis and Swartkloofberg formations due to laterally variable accommodation space within the foreland basin. Strata of the Swartkloofberg Formation are interpreted as flysch deposits within an underfilled basin. We propose that the distinct deltaic peritidal and shoreface strata that—in some localities—were previously assigned to the upper Nomtsas Formation, are placed within the unconformably overlying molasse deposits of the Fish River Subgroup. These strata contain the stratigraphically lowest identified occurrences ofTreptichnus pedumwithin the Nama Group, and thus the base of the Cambrian Period. This stratigraphic revision solves several longstanding issues with regional correlation and revises the position of the Ediacaran–Cambrian boundary in the Witputs Subbasin. Accordingly, the Swartkloofberg Formation in the Witputs Subbasin (538.5–<537.6 Ma) is Ediacaran in age, as defined by biostratigraphy, supporting recent interpretations that the base of the Cambrian Period may be younger than 537.6 Ma. With increasingly refined age-stratigraphic models for the Nama Group, the upper Schwarzrand Subgroup provides a high-resolution record of the evolution of increasingly complex benthic invertebrate behaviors in the terminal Ediacaran lead-up to the classical Cambrian radiation of biomineralized invertebrate phyla. 

ABSTRACT Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft‐bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in‐depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life. 

The Nama Group of Namibia and South Africa preserves an extraordinary record of marine ecosystems existing in the lastc. 15 myr of the Ediacaran, comprising enigmatic and soft-bodied fossils that are part of the first major radiation of macroscopic life. Since their description at the beginning of the 20th century these fossils have played an important role in debates surrounding the affinities of iconic Ediacaran fossil groups, and ash beds preserved throughout the succession have been crucial to understanding rates and patterns of early animal evolution. Fossils preserved in varying contexts have allowed for detailed reconstructions of Ediacaran palaeobiology, and geochemical analyses provide a window into understanding the controls on Ediacaran taphonomic pathways, including crucial, and potentially widespread, roles played by clay minerals in exceptional fossil preservation. 

Himatiichnus manganoigen. et isp. nov., a new trace fossil from the late Ediacaran Huns Member of the Urusis Formation, southern Namibia, comprises intertwining tubes exhibiting dual lineation patterns and reminiscent of both modern and early Cambrian examples of priapulid worm burrows. These similarities support the interpretation of a total-group scalidophoran tracemaker forH. mangano, thus providing direct evidence for the first appearance date of Scalidophora in the late Ediacaranca539 Ma. This new material is thus indicative of the presence of total-group scalidophorans below the Cambrian boundary and supports inference of a lengthy Precambrian fuse for the Cambrian explosion. 

The rise of animals across the Ediacaran–Cambrian transition marked a step-change in the history of life, from a microbially dominated world to the complex macroscopic biosphere we see today.1,2,3 While the importance of bioturbation and swimming in altering the structure and function of Earth systems is well established,4,5,6 the influence of epifaunal animals on the hydrodynamics of marine environments is not well understood. Of particular interest are the oldest “marine animal forests,”7 which comprise a diversity of sessile soft-bodied organisms dominated by the fractally branching rangeomorphs.8,9 Typified by fossil assemblages from the Ediacaran of Mistaken Point, Newfoundland,8,10,11 these ancient communities might have played a pivotal role in structuring marine environments, similar to modern ecosystems,7,12,13 but our understanding of how they impacted fluid flow in the water column is limited. Here, we use ecological modeling and computational flow simulations to explore how Ediacaran marine animal forests influenced their surrounding environment. Our results reveal how organism morphology and community structure and composition combined to impact vertical mixing of the surrounding water. We find that Mistaken Point communities were capable of generating high-mixing conditions, thereby likely promoting gas and nutrient transport within the “canopy.” This mixing could have served to enhance local-scale oxygen concentrations and redistribute resources like dissolved organic carbon. Our work suggests that Ediacaran marine animal forests may have contributed to the ventilation of the oceans over 560 million years ago, well before the Cambrian explosion of animals. 

Sponge-grade Archaeocyatha were early Cambrian biomineralizing metazoans that constructed reefs globally. Despite decades of research, many facets of archaeocyath palaeobiology remain unclear, making it difficult to reconstruct the palaeoecology of Cambrian reef ecosystems. Of specific interest is how these organisms fed; previous experimental studies have suggested that archaeocyaths functioned as passive suspension feeders relying on ambient currents to transport nutrient-rich water into their central cavities. Here, we test this hypothesis using computational fluid dynamics (CFD) simulations of digital models of select archaeocyath species. Our results demonstrate that, given a range of plausible current velocities, there was very little fluid circulation through the skeleton, suggesting obligate passive suspension feeding was unlikely. Comparing our simulation data with exhalent velocities collected from extant sponges, we infer an active suspension feeding lifestyle for archaeocyaths. The combination of active suspension feeding and biomineralization in Archaeocyatha may have facilitated the creation of modern metazoan reef ecosystems. 

The stem-group euarthropodAnomalocaris canadensisis one of the largest Cambrian animals and is often considered the quintessential apex predator of its time. This radiodont is commonly interpreted as a demersal hunter, responsible for inflicting injuries seen in benthic trilobites. However, controversy surrounds the ability ofA. canadensisto use its spinose frontal appendages to masticate or even manipulate biomineralized prey. Here, we apply a new integrative computational approach, combining three-dimensional digital modelling, kinematics, finite-element analysis (FEA) and computational fluid dynamics (CFD) to rigorously analyse anA. canadensisfeeding appendage and test its morphofunctional limits. These models corroborate a raptorial function, but expose inconsistencies with a capacity for durophagy. In particular, FEA results show that certain parts of the appendage would have experienced high degrees of plastic deformation, especially at the endites, the points of impact with prey. The CFD results demonstrate that outstretched appendages produced low drag and hence represented the optimal orientation for speed, permitting acceleration bursts to capture prey. These data, when combined with evidence regarding the functional morphology of its oral cone, eyes, body flaps and tail fan, suggest thatA. canadensiswas an agile nektonic predator that fed on soft-bodied animals swimming in a well-lit water column above the benthos. The lifestyle ofA. canadensisand that of other radiodonts, including plausible durophages, suggests that niche partitioning across this clade influenced the dynamics of Cambrian food webs, impacting on a diverse array of organisms at different sizes, tiers and trophic levels.