Ediacaran discoidal impressions and related structures from Newfoundland, Canada and the Long Mynd, Shropshire, UK: their nature and biogenicity
Bibliographic record
Abstract
The nature of the Ediacaran macrobiota (c. 580-541 Ma) remains puzzling. These first assemblages of large, complex fossils may have included early animals; giant microbial forms; and organisms representing radically different body plans that went extinct. Discoidal impressions – some forming the base of Ediacaran fronds but most found as isolated discs – dominate the Ediacaran macrobiota. However round markings may also be formed in a variety of abiogenic ways. This study investigates the nature and biogenicity of discoidal impressions from two Ediacaran successions: the c. 560-Ma upper Burway Formation, Longmyndian Supergroup, Shropshire, UK; and several sites on the Bonavista and Avalon Peninsulas, Newfoundland, Canada, ranging in age from 565–c. 560 Ma. The investigation involved fieldwork, photography, serial grinding through cross-sections, and optical and scanning electron microscopy. It concludes that several Longmyndian discoidal forms are pseudofossils formed by sediment injection resulting from small-scale fluid escape inferred to be driven by microbial mat sealing. Turning to clearly biogenic impressions, comparison of the varied morphologies of holdfast discs associated with fronds preserved under ash and sand from several Newfoundland sites leads to a generic model of their architecture as consisting of enclosed chambers, a complex construction perhaps for strength or possibly symbiosis. Detailed observations of the rayed disc Hiemalora suggest that it may have had an amoeboid lifestyle. Finally, the key Ediacaran taxon Aspidella is separated from the discs Ediacaria and Spriggia, with which it has been synonymized, and interpreted as a possible polyp-like animal capable of limited movement. This thesis thus demonstrates that the earliest reported Ediacaran discoidal impressions are abiogenic, produced by mat-influenced processes particularly relevant to the Precambrian, and proposes models and interpretations for several key Ediacaran forms that have important implications for both the nature and diversity of the Ediacaran macrobiota, and early animal evolution.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".