From form to flow: reconstructing the life posture and hydrodynamics of iconic Ediacaran taxa
Bibliographic record
Abstract
The Ediacaran successions of Newfoundland include some of the oldest macroscopic candidate metazoans. These fossils are preserved as two-dimensional near-census assemblages on deep-marine volcaniclastic sediments beneath tuffites. The communities, dominated by the frondose morphogroups Rangeomorpha and Arboreomorpha, were traditionally interpreted as consisting primarily of erect taxa that had been felled and aligned by paleocurrents, alongside some randomly oriented reclining forms. However, in the absence of sedimentological evidence, paleocurrent direction has been inferred from fossil orientation, despite the unresolved posture of many of these organisms in life. This PhD focuses on the Melrose Surface near the Catalina Dome of the Discovery UNESCO Global Geopark, which provides sedimentological evidence for current direction in the form of current ripples and cross-lamination. This site offers a unique opportunity to reconstruct the life position and orientation of Ediacaran taxa relative to sedimentologically-determined paleocurrents. An integrative approach has been employed herein, combining different strategies detailed in three papers: 1. Taphonomic reinterpretation of the genus Charniodiscus: by examining the taphonomic clues of the type material C. concentricus, this taxon was reconstructed as a conical bifoliate erect/recumbent frond, distinguishing it from reclining arboreomorphs such as C. procerus (present in the surface), which shows consistently extraordinary stem preservation across stratigraphic units. 2. Clustering algorithms on Fractofusus misrai orientations: using novel statistics based on modified polythetic and monothetic clustering techniques adapted to circular variables, preferential orientation trends oblique to the paleocurrent were identified in the population of F. misrai from the Melrose Surface. 3. Computational Fluid Dynamics (CFD) over Fractofusus misrai: turbulent flows were modeled to understand the hydrodynamic phenomena associated with highly detailed reconstructions F. misrai. The preferential orientations found on the Melrose Surface result from a balance between maximizing aspect ratio for feeding efficiency and reducing current-induced drag. This work presents an integrative approach based on taphonomy, statistics, and CFD to reconstruct the position of Ediacaran taxa and the currents they lived in. The papers challenge the assumed erect position for all arboreomorphs and the random orientation for reclining rangeomorph taxa. This thesis advocates for interpreting fossils as reclining flat, responding rheotropically to paleocurrents, unless evidence supports otherwise.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.004 | 0.003 |
| Science and technology studies | 0.000 | 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) | 0.002 | 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".