The new problem of Chinlestegophis and the origin of caecilians (Amphibia, Gymnophionomorpha) is highly sensitive to old problems of sampling and character construction
Bibliographic record
Abstract
The description of the small Late Triassic temnospondyl Chinlestegophis ushered in a potentially radically new understanding of the origins of the extant amphibian clades. Together with the fragmentary Rileymillerus, Chinlestegophis was argued to link extant caecilians to Permo-Triassic stereospondyl temnospondyls rather than to frogs and salamanders (and through them to amphibamiform temnospondyls or to brachystelechid and lysorophian “lepospondyls”). We critically review the comparative description of Chinlestegophis and phylogenetic analyses of previous studies. Most of the features previously interpreted to be shared by caecilians, Chinlestegophis and/or other stereospondyls have different distributions than scored in the analysis. We also find no evidence for an incipient tentacular sulcus in Chinlestegophis, and note that its vertebrae, unreduced ribs and dermal shoulder girdle are unlike those of any extant amphibians (nor their likely sister group, Albanerpetidae). Furthermore, the original matrices contain misscores accreted over more than a decade that likewise influence the results. Some features are coded as multiple redundant characters: the double toothrow of Chinlestegophis, other stereospondyls, and caecilians is represented as seven characters. Analysis of the unmodified matrix yields much less resolution than originally reported, and tree topology is altered by a small change to the taxon sample (the addition of Albanerpetidae), limited revisions of irreproducible scores, and ordering the most obviously clinal characters; any one of these changes removes Chinlestegophis from Lissamphibia, and confirms it as a stereospondyl.
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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 | 0.001 | 0.002 |
| 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 | 0.003 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".