Remarkable fossils on unremarkable bedding planes? The role of true substrates in the fossil record of the Ediacaran macrobiota
Bibliographic record
Abstract
Strata from the late Ediacaran Period (∼579-539 Ma) host fossils of Earth's earliest assemblages of diverse macroscopic organisms: the Ediacaran macrobiota. Many Ediacaran macrobiota taxa are preserved as cast-and-mould impressions of wholly soft-bodied organisms on the tops or bases of beds (termed here ‘Ediacaran Impression Fossils’, or EIFs). Occurrences of EIFs are frequently interpreted to preserve in situ palaeocommunities representative of original ecosystems. Observations of the bed-scale sedimentology associated with EIFs in the Mistaken Point Formation of Newfoundland (Avalon-type biota), Rawnsley Quartzite of South Australia (White Sea-type biota) and Kuibis/Schwarzrand subgroups of Namibia (Nama-type biota) suggest in situ burial was favoured in scenarios of high sediment supply and concentrations, in conjunction with elevated aggradation rates, which together suppressed local turbulence and limited erosional scour. The resulting fossiliferous surfaces can be regarded as true substrates - surfaces preserving the sediment-water interface in instances where intervals of sedimentary stasis were succeeded by depositional events without associated erosion. We here examine key factors that underpin true substrate construction against the record of in situ EIFs in space and time and discuss the implications of considering EIFs within a true substrate framework. Our assessments highlight several points: 1) EIF preservation is facilitated in the first instance by routine compound sedimentation states where the state immediately preceding the burying bed was one of stasis, with any post-deposition modification (e.g., following decomposition of the entombed organic matter) only minimally impacting the final record; 2) Burial may occur at any stage of community colonization, growth, shifts in morphology in response to environmental triggers, functional collapse, or individual decay and degradation; 3) True substrates hold variable amounts of stratigraphic time, complicating comparison of community ecology between different Ediacaran biotic assemblages; and 4) The availability and accessibility of certain sedimentary facies more amenable to true substrate preservation will impact the apparent distribution of the Ediacaran macrobiota. Future research on Ediacaran impression fossils requires consideration of sedimentation regimes and bed construction to decouple biases inherent to these processes from genuine biological signals.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".