A new ‘acanthothoracid’ placoderm from the Arctic Canada (Early Devonian) and its bearing on the evolution of jaws and teeth
Bibliographic record
Abstract
The origin of jaws and teeth represents one of the most formative episodes in our own evolutionary history. However, this event is poorly understood because of a lack of detailed knowledge of key lineages, including the ‘acanthothoracid’ placoderms, which were among the earliest jawed vertebrates. Here, we describe Romundina gagnieri sp. nov., a new species of ‘acanthothoracid’ from the Early Devonian of Arctic Canada. The new species displays anterior supragnathal plates with teeth that we have characterized using synchrotron tomography. Our study shows that teeth are arranged in a concentric manner and that the pattern of tooth addition is centrifugal, including an anterior addition. Overgrowing odontodes, present on the anterior part of the gnathal plates, are covering teeth that can display an hypermineralized layer (probably reflecting the earliest stage of teeth during the ontogeny) or be partially broken. These overgrowing odontodes develop in successive steps and without obvious organization. The presence of a pair of anterior supragnathal plates on the ethmoid part of the endocranium, as well as the growth process of these plates in R. gagnieri sp. nov. are similar to the conditions seen notably in arthrodires, compatible with an ancestral gnathostome ancestral condition.
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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 | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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 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".