Tonian Macroalgae from the Mackenzie Mountain Supergroup in the Wernecke Mountains, Yukon Territory
Bibliographic record
Abstract
Early eukaryotic fossils are crucial to understanding the evolution of the Earth's biosphere and geosphere. Molecular clock estimates suggest that crown-group members of key algal lineages evolved and diversified by the Tonian Period (1000 to 720 Ma), but this diversification is poorly reflected in the fossil record. Previously undocumented, centimeter-scale macrofossils were recovered from the outer shelf marine facies of the ca. 950 Ma Dolores Creek Formation, Wernecke Mountains (northwestern Canada, Chapter 2). Three distinct size classes were identified. The larger fossils are interpreted as eukaryotic macroalgae with a likely green algal affinity, making them among the oldest macroalgae yet recognized and filling a critical gap in algal evolution. Analytical microscopy, including scanning electron microscopy and tomographic x-ray microscopy, were used to investigate fossil preservation and develop a taphonomic model (Chapter 3). The fossil preservation consists of pyritization and aluminosilicification, similar to accessory mineralization observed in the Paleozoic Burgess Shale-type preservation. The macroalgae are defined as a new genus and species based on their morphology including an unbranching, uniseriate thallus with uniform width and elliptical to globose holdfasts (Chapter 4). Larger specimens are classified as probable vendotaenids while smaller mm-scale specimens display branching but remain undefined as a form taxon as theylack distinguishing morphological characteristics. The unstable redox conditions that defined the macroalgae's paleoenvironment in the Wernecke Mountains were constrained using geochemical analyses (Fe speciation, major/trace elements, and TOC, Chapter 5). Considering the macroalgae within a paleoenvironmental context allows us to place realistic constraints on these organism's paleoecology and paleobiology. The Dolores Creek macroalgae along with the recently reported ca. 1000 Ma multicellular chlorophyte from North China and ca. 1000 Ma photosynthetic, eukaryotic algae from the Congo Basin, provide evidence that benthic green algae colonized shallow marine habitats by the early Tonian Period. These discoveries indicate that there are glaring omissions in the fossil record that need to be addressed in future studies by recovering new fossils and characterizing their habitats to aid in reconstructing the late Proterozoic biosphere.
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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 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".