A Paleozoic stem hagfish <i>Myxinikela siroka</i> — revised anatomy and implications for evolution of the living jawless vertebrate lineages
Bibliographic record
Abstract
Hagfishes and lampreys comprise cyclostomes, the earliest branching and sole surviving clade of the once diverse assemblage of jawless crown-group vertebrates. Lacking mineralized skeletons, both of the crown cyclostome lineages have notoriously poor fossil record. Particularly in the hagfish total group, †Myxinikela siroka Bardack, 1991 from the Late Carboniferous estuarine system of Illinois (USA) represents the only definitive stem taxon. Previously known from a single specimen, Myxinikela has been reconstructed as a short-bodied form with pigmented eyes but otherwise difficult to distinguish from the living counterpart. With a new, second specimen of Myxinikela reported here, I reevaluate the soft tissue anatomy and formulate diagnosis for the taxon. Myxinikela has a number of general features of cyclostomes, including cartilaginous branchial baskets, separation between the esophageal and the branchial passages, and a well-differentiated midline finfold. In effect, these features give more lamprey-like appearance to this stem hagfish than previously assumed. Myxinikela still has many traits that set modern hagfishes apart from other vertebrates (e.g., nasohypophyseal aperture, large velar cavity, and cardinal heart) and some intermediate conditions of modern hagfishes (e.g., incipient posterior displacement of branchial region). Thus, Myxinikela provides an important calibration point with which to date origins of these characters.
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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 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".