On the origins of marine‐derived freshwater fishes in South America
Bibliographic record
Abstract
Abstract Aim The South American fish fauna is renowned for its extraordinary diversity. The majority of this diversity is restricted to few major clades that have ancient associations to freshwater habitats. However, at a higher taxonomic level, the South American ichthyofauna is enriched by an extraordinary number of marine derived lineages – lineages that are endemic to freshwaters, but derived from marine ancestors. Here, we test palaeogeographical hypotheses that attempt to explain the origins and exceptional diversity of marine derived fishes in rivers of South America. Location South America. Methods We analysed time‐calibrated molecular phylogenies, ancestral reconstructions and biogeographical patterns for multiple independent marine‐derived lineages. Results Five of the ten marine‐derived lineages in our analysis have biogeographical patterns and stem ages consistent with invasion from the Atlantic Ocean during the Oligocene or Eocene. Drums and pufferfishes reveal patterns and ages that were consistent with the Miocene marine incursion hypothesis. The Amazonian halfbeak is the only lineage younger than the Miocene and invaded Amazonian freshwaters less than a million years ago. Main Conclusion Our results suggest Miocene marine incursions and the Pebas Mega‐Wetland may not explain the high diversity of marine derived lineages in South America. Instead, the Pebas Mega‐Wetland may have created a fertile opportunity for diversification of some, but not all marine‐derived lineages.
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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 | 0.001 | 0.000 |
| 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 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".