The relative influence of niche vs. neutral processes in ecosystem dynamics is an on‐going debate, but the extent to which they structured the earliest animal communities is unknown. Some of the oldest known metazoan‐dominated paleocommunities occur in Ediacaran age (~ 565 million years old) strata in Newfoundland, Canada and Charnwood Forest, UK. These comprise large and diverse populations of sessile organisms that are amenable to spatial point process analyses, enabling inference of the most likely underlying niche or neutral processes governing community structure. We mapped seven Ediacaran paleocommunities using LiDAR, photogrammetry and a laser line probe. We found that neutral processes dominate these paleocommunities, with niche processes exerting limited influence, in contrast with the niche‐dominated dynamics of modern marine ecosystems. The dominance of neutral processes suggests that early metazoan diversification may not have been driven by systematic adaptations to the local environment, but instead may have resulted from stochastic demographic differences.

Molecular timescales estimate that early animal lineages diverged tens of millions of years before their earliest unequivocal fossil evidence. The Ediacaran macrobiota (~574 to 538 million years ago) are largely eschewed from this debate, primarily due to their extreme phylogenetic uncertainty, but remain germane. We characterize the development of Charnia masoni and establish the affinity of rangeomorphs, among the oldest and most enigmatic components of the Ediacaran macrobiota. We provide the first direct evidence for the internal interconnected nature of rangeomorphs and show that Charnia was constructed of repeated branches that derived successively from pre-existing branches. We find homology and rationalize morphogenesis between disparate rangeomorph taxa, before producing a phylogenetic analysis, resolving Charnia as a stem-eumetazoan and expanding the anatomical disparity of that group to include a long-extinct bodyplan. These data bring competing records of early animal evolution into closer agreement, reformulating our understanding of the evolutionary emergence of animal bodyplans.

The Ediacaran fossils of the Mistaken Point E surface have provided crucial insight into early animal communities, including how they reproduced, the importance of Ediacaran height and what the most important factors were to their community dynamics. Here, we use this iconic community to investigate how morphological variation between eight taxa affected their ability to withstand different flow conditions. For each of Beothukis, Bradgatia, Charniodiscus procerus, Charniodiscus spinosus, Plumeropriscum, Primocandelabrum, Thectardis and Fractofusus we measured the orientation and length of their stems (if present) and their fronds. We statistically tested each taxon’s stem and frond orientation distributions to see whether they displayed a uniform or multimodal distribution. Where multimodal distributions were identified, the stem/frond length of each cohort was tested to identify if there were differences in size between different orientation groups. We find that Bradgatia and Thectardis show a bimodal felling direction, and infer that they were felled by the turbulent head of the felling flow. In contrast, the frondose rangeomorphs including Beothukis, Plumeropriscum, Primocandelabrum, and the arboreomorphs were felled in a single direction, indicating that they were upright in the water column, and were likely felled by the laminar tail of the felling flow. These differences in directionality suggests that an elongate habit, and particularly possession of a stem, lent greater resilience to frondose taxa against turbulent flows, suggesting that such taxa would have had improved survivability in conditions with higher background turbulence than taxa like Bradgatia and Thectardis, that lacked a stem and had a higher centre of mass, which may have fared better in quieter water conditions.

35The relative influence of niche versus neutral processes in ecosystem dynamics is a 36 fundamental question in community ecology, but the extent to which they structured early 37 animal communities is unknown. The oldest known metazoan-dominated paleocommunities 38 occur in Ediacaran age (~565 million years old) strata in Newfoundland, Canada and 39 Charnwood Forest, UK. These comprise large and diverse in-situ populations of sessile 40 organisms that are amenable to spatial point process analyses, enabling inference of the most 41 likely underlying niche or neutral processes governing their community structure. We 42 conducted comprehensive spatial mapping of seven of the largest Ediacaran 43 paleocommunities using LiDAR, photogrammetry and a laser-line probe. We find neutral 44 processes to dominate these paleocommunities with limited influence of niche processes. 45Our results differ from the niche-dominated dynamics of modern marine ecosystems, 46 revealing that the dynamics of environmental interactions prompted very different ecosystem 47 structuring for these early animal communities. 48 49 50Two opposing theories lie at the heart of debate regarding the fundamental mechanisms that 51 govern ecosystem structure and biodiversity: niche and neutral. Niche theory is a central 52 tenet of classical ecological theory, whereby species avoid competitive exclusion by 53 occupying different niches within the ecosystem (1). Smaller niche overlaps result in less 54 competition between taxa, permitting numerous taxa to exist in an area without excluding 55 each other. Species are able to co-exist because they have different requirements. Niche 56 models describe selection-dominated ecosystems, whereby species dynamics operate 57 deterministically as a series of inter-specific interactions, which act as stabilizing mechanisms 58 for the ecosystem (2). 59 60 Neutral processes are often referred to as the 'null model' of niche processes: instead of 61 species differences enabling co-existence, it is their similarities that drive high diversity (3). 62Within neutral models, species fitness is similar across a community, and so different taxa 63 can co-exist because no single taxon has a significant competitive advantage over any other. 64Despite this seemingly unrealistic assumption, neutral theories have been able to accurately 65 reproduce certain species-area-distributions (3) and beta diversity patterns (4, 5), sometimes 66 better than niche theories (1). 67 68In recent years, unified or continuous theories have emerged, whereby niche and neutral 69 processes combine to enable species coexistence (2, 6). In these combined models, species 70 can exhibit strong differences and strong stabilizations (niche-type), or similar fitness and 71 weak stabilizations (neutral-type), with the classic niche and neutral models forming the 72 extreme end-members of this continuum model. However, it is often not possible to select 73 5 the best-fit niche or neutral model, making it difficult to disentangle the relative influence of ...