Galloanseran cranial development highlights exceptions to von Baer’s laws
Bibliographic record
Abstract
The remarkable morphological disparity of the animal kingdom is underpinned by changes in embryonic development across the tree of life; as such, deciphering evolutionary patterns of developmental divergence depends on investigations of different species across a range of comparable developmental stages. Among the most influential ideas regarding such developmental divergences are von Baer's Laws of Development and Haeckel's Theory of Recapitulation. Here, we assess several predictions following from these ideas at the tissue-level by comparing skull osteogenesis in representatives of the bird clade Galloanserae. We investigated high-resolution µCT scans of embryonic series for four galloanseran species: chickens and quails, representing Galliformes (landfowl), and ducks and geese, representing Anseriformes (waterfowl). To compare skull osteogenesis across our taxon sample, we devised a skull-specific staging system based on ossification sequences to discretise the process into five stages. During skull osteogenesis, we found that the location of the onset of ossification within each element and the direction of ossification progression were the same in all species in our sample, implying a conserved developmental programme for induction and ossification progression across Galloanserae. Moreover, we found that the appearance of synapomorphies diagnostic of broader clades often overlapped with species-specific ones during osteogenesis. Indeed, many diagnostic features of deep clades, such as osteological synapomorphies of the phylogenetically inclusive clade Galloanserae, appear at surprisingly late stages of development. These observations fail to support several predictions of von Baer's Laws of Development and Haeckel's Theory of Recapitulation, instead suggesting what we term a 'braiding' pattern of developmental divergence in which degrees of interspecific morphological similarity wax and wane during development as a result of the interplay between developmental constraints and phyletic variation.
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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 | 0.001 | 0.004 |
| 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 | 0.003 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".