Digital restoration of the pectoral girdles of two Early Cretaceous birds, and implications for early flight evolution
Bibliographic record
Abstract
Abstract Pectoral girdle morphology is a key determinant of flight capability, but in some respects is poorly known among stem birds. Here, we reconstruct the pectoral girdles of the Early Cretaceous birds Sapeornis and Piscivorenantiornis based on computed tomography and three-dimensional visualization, revealing key morphological details. Enantiornithines such as Piscivorenantiornis have a uniquely localized scapula-coracoid joint, with only one area of articulation. This single articulation contrasts with the double articulation widely present in non-enantiornithine pennaraptoran theropods, including Sapeornis and crown birds, which comprises main and subsidiary articular contacts. A partially closed triosseal canal occurs in non-euornithine birds, representing a transitional stage in flight apparatus evolution. Numerous modifications of the pectoral girdle along the line to crown birds, and lineage-specific pectoral girdle variations, produced diverse pectoral girdle morphologies among Mesozoic birds, which ensured that a commensurate range of capability levels and modes emerged during the early evolution of flight.
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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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".