Reevaluation of the homology of bones of the cranial vault in tetrapod vertebrates
Bibliographic record
Abstract
Homology assessments of bones are made using one or more criteria (e.g., topology, development, phylogeny). In tetrapods, the bones of the cranial vault appear highly conserved topologically. However, recent fate maps have revealed key differences in the embryonic origin of bones of the cranial vault in representatives of two amniote lineages. In mouse, the frontal is derived from cranial neural crest (CNC) and the parietal of mesoderm, placing the CNC-mesoderm boundary at the suture between these bones. In chicken, by contrast, this boundary is located within the frontal, which thus has a dual embryonic origin. This difference is seemingly inconsistent with the traditional assessment of homology of the avian frontal with that of mammals and other tetrapods. To elucidate this apparent conflict, we fate-mapped CNC and mesoderm using GFP-transgenic axolotls to reveal specific contributions to the cranial vault. The CNC-mesoderm boundary in axolotl is located between frontal and parietal, as in mouse, but differs from that in chicken. If, however, the avian frontal is instead regarded as a fused frontal and parietal (i.e., frontoparietal) and the parietal a postparietal, then the avian cranial vault remains topologically congruent, and becomes developmentally congruent, with that of both urodeles and mammals. This hypothesis is supported by data from the fossil record: a separate frontal, parietal and postparietal is present in all stem lineages of extant taxa, including birds. Moreover, it implies that a postparietal is/was present in non-avian archosaurs but likely fuses early in ontogeny to the parietal (or supraoccipital), as it does in many extant mammals.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".