Embryonic origins of novelty and constraint in the amniote upper jaw
Bibliographic record
Abstract
Mammals, birds, and reptiles exhibit remarkable diversity in the shape, size, and relative proportions of the upper jaw. Determining when these differences are generated is critical to our understanding of how developmental mechanisms impact evolutionary diversification. Here we demonstrate that all major amniote lineages share a common pattern of embryonic shape and growth up until fusion of the facial primordia. Subsequent to fusion, avian and non‐avian lineages diverge in Sonic hedgehog (SHH) signaling domain expression, leading to lineage‐specific alterations in facial proportions. As a result, the avian upper jaw is composed primarily of frontonasal derivatives, while in non‐avian amniotes the maxillary derivatives comprise the largest proportion of the jaw, in both cases regardless of overall snout length. Experimental manipulation of pre and post‐fusion SHH‐domains in avians phenocopies the proportions of non‐avian amniote upper jaws. This developmental sequence of early conservation followed by later diversification demonstrates that fusion of the facial primordia is a critical prerequisite to evolutionary divergence of the upper jaw, while regulation of SHH‐signaling mediated postfusion growth processes is an important mechanism by which evolutionary variation in jaw shape is generated.
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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 | 0.000 | 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 | 0.001 |
| 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".