Fusion in the vertebral column of the pachyosteomorph arthrodire Dunkleosteus terrelli (‘Placodermi’)
Bibliographic record
Abstract
Fusion in the vertebral column has evolved multiple times within jawed vertebrates and for these taxa represents normal physiology, with structures such as the sacrum, notarium and pygostyle providing rigidity and support.The synarcual represents the fusion of the anterior part of the vertebral column and occurs in a number of jawed vertebrates, including a variety of placoderms, chondrichthyans and mammals.Placoderms are an entirely fossil group of armoured fishes (Silurian-Devonian), resolved phylogenetically to the base of the jawed vertebrate clade, with vertebrae comprising neural and haemal arches composed of perichondral bone.The placoderm synarcual preserves substantial developmental information from anterior (oldest) to posterior, where new vertebrae are incorporated.This developmental sequence was described recently in the phyllolepid arthrodire Cowralepis mclachlani and ptyctodonts such as Materpiscis attenboroughi, although finer developmental details were not visible.We describe the synarcual in a subadult specimen of the pachyosteomorph arthrodire Dunkleosteus terrelli, preserving 16 paired vertebral elements showing varying degrees of anteroposterior fusion along the vertebral column.Micro-CT scanning of the synarcual provides details of a transitional zone of vertebral modification (involving four of these paired vertebrae, posteriorly), providing unprecedented information on how each vertebra is altered and incorporated into the synarcual.Some of the synarcual elements still retain substantial vertebral identity, showing less fusion overall, thus being more comparable to other arthrodires such as Compagopiscis.By comparison, synarcuals of other taxa, such as the ptyctodont placoderms, along with batoids, holocephalans (Chondrichthyes) and mammals (syncervical) show more complete fusion of vertebral elements.
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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 | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 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".