Late Cretaceous invasion of Madagascan fresh waters by percomorph fishes (Teleostei: Acanthomorpha)
Bibliographic record
Abstract
Numerous isolated elements from freshwater Upper Cretaceous (Maastrichtian) deposits in the Mahajanga Basin of northwestern Madagascar are identified as belonging to acanthomorph fishes. Multiple specimens representing the same bony element, including vertebrae, fin spines, basioccipitals, dentaries, hyomandibulae, anguloarticulars, and premaxillae (with a few other elements such as a vomer and a quadrate being less numerous), document the presence of several different morphologies that are indicative of at least three species. The morphologies of the elements, however, are broadly similar to one another, and we interpret this to be a reflection of their shared ancestry and identify the multiple species as representing a single lineage. Therefore, the material likely documents a single invasion of Madagascan fresh waters by a marine lineage, followed by the diversification of this lineage into several taxa within the freshwater environment. A less parsimonious scenario would be that the lineage may have diversified first in marine waters followed by several independent invasions of freshwaters by the most closely related lineages, which seems less likely. Most known Cretaceous acanthomorphs belong to Paracanthopterygii or early-diverging groups of Acanthopterygii, with few belonging to Percomorpha. The material reported here documents the presence of percomorphs in Upper Cretaceous freshwater deposits of Madagascar, the first from Eastern Gondwana and only the second from all of Gondwana. Additionally, the Madagascan acanthomorphs are much larger than most of those previously reported from Albian through Campanian marine and freshwater deposits, indicating that by the latest Cretaceous acanthomorph fishes had evolved relatively large body forms, at least in Eastern Gondwana.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".