A revision of the anatomy of the Early Devonian jawed vertebrate<i>Ptomacanthus anglicus</i>Miles
Bibliographic record
Abstract
Abstract: The spine‐bearing jawed vertebrates (gnathostomes) assigned to the assemblage ‘Acanthodii’ play a key role in understanding the early evolution of osteichthyans and chondrichthyans. Amongst ‘acanthodians’, the genusPtomacanthushas played a prominent role owing to its shark‐like tooth files. Recently described braincase material from this taxon contrasts strongly with the osteichthyan‐like braincase ofAcanthodes, the only other ‘acanthodian’ for which this anatomy is well known. This seriously challenges acanthodian monophyly or at least the prevailing interpretation ofAcanthodes. This study presents a redescription and updated comparison of the anatomy ofPtomacanthusbased on unfigured material from the type and referred specimens, as well as adding new data on spine and scale histology.Ptomacanthusis remarkably heterosquamous compared to some other ‘acanthodians’. Further to its resemblances toClimatius,Ptomacanthusshares some features of the external morphology of its scales with the enigmatic genusObtusacanthus. The scale crowns ofPtomacanthusexhibit both superpositional and areal growth. The bases, however, grow separately from the crown. As inAcanthodes, scales are here inferred to be added to the body from posterior to anterior. In spite of its chondrichthyan‐like form and characters,Ptomacanthusremains difficult to place on either the chondrichthyan, osteichthyan or gnathostome stem. Different placements each require invoking considerable character incongruence. Nevertheless, these new data fromPtomacanthusprovide broader anatomical context for hard tissue characters commonly described on the basis of isolated remains.
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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 | 0.002 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 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".