Forelimb reduction and digit loss were evolutionarily decoupled in oviraptorosaurian theropod dinosaurs
Bibliographic record
Abstract
. A wealth of work has sought to understand the evolution of bird flight via arm elongation, but despite widespread occurrences of forelimb reduction and digit loss throughout theropod dinosaurs, the evolutionary drivers behind these patterns are poorly understood. Previous studies demonstrate broad allometric trends that can account for some instances of forelimb reduction, but the repeated loss of digits, and their hypothesized link to forelimb shortening, has received less attention. Here, we evaluate evolutionary associations between digit loss and forelimb reduction in an iconic and data-rich theropod clade, Oviraptorosauria. Unexpectedly, we find that the evolution of digit III and the rest of the forelimb are decoupled. Support for different evolutionary models and a lower phylogenetic signal in digit III than the rest of the forelimb suggests these segments were subject to different evolutionary processes leading to independent morphological change. Oviraptorosaurs exhibit four distinct forelimb morphotypes, but these do not exactly correspond to patterns of dietary niche partitioning. Overall, forelimb evolution in oviraptorosaurs is more complex than anticipated, potentially as a result of an evolutionary radiation they underwent in the Late Cretaceous.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".