Fossil constraints on the origin and evolution of Platyhelminthes are surprisingly concordant with modern molecular phylogenies
Bibliographic record
Abstract
Trace fossils preserved with fossil worm-shaped remains suggest the presence of free-living flatworms during the Ordovician at the latest and their occurrence in terrestrial environments during the Permian. The presence of hooks associated with acanthodian and placoderm fishes indicates the existence of parasitic monopisthocotyleans, with a simple life cycle, during the Devonian. The presence of eggs in shark coprolites suggests the occurrence of eucestode tapeworms, with complex life cycles, during the Permian, possibly even earlier in the Carboniferous. Fossil evidence for trematode flatworms, also with complex life cycles, is more recent, including diverse findings associated with bivalves, lizards, and coprolites of archosaurs in terrestrial environments between 126 and 76 Ma in the Cretaceous. Convincing evidence for gymnophallid trematodes in marine environments appears in the Eocene, with an earlier occurrence in Cretaceous freshwater environments. This chronological pattern of first appearance (Turbellarians > Monopisthocotylea > Cestoda > Trematoda) is surprisingly concordant with some recent molecular phylogenetic analyses. Further evidence to test these hypotheses could be obtained by conducting systematic screenings for resistant remains of platyhelminths such as hooks and eggs as well as characteristic traces such as trails or shell concretions preserved with their producers. Additional study and scrutiny are particularly needed for trace fossils attributed to free-living flatworms that are not associated with their producers. We make recommendations on how different constraints on flatworm evolution can be interpreted and used in future studies.
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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 | 0.000 | 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 | 0.000 | 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".