Cursorial ecomorphology and temporal patterns in theropod dinosaur evolution during the mid-Cretaceous
Bibliographic record
Abstract
Coelurosauria, including modern birds, represents a successful group of theropod dinosaurs that established a high taxonomic diversity and significant morphological modifications. In the evolutionary history of this group, a specialized foot morphology, the arctometatarsus, evolved independently in several lineages and has been considered an adaptation for cursoriality. While its functional significance has been extensively studied, the temporal pattern of this parallel evolution, as well as its origin and influencing factors, remains largely unresolved. Here, we show the temporal evolution of cursorial traits, including the arctometatarsus and hind limb proportions. Our study reveals that the proportional elongation of distal hind limb segments preceded the evolution of the arctometatarsus in ornithomimosaurs and oviraptorosaurs. In contrast, in tyrannosauroids, alvarezsaurs and troodontids, the proportional elongation of the tibia and metatarsals occurred in parallel with the acquisition of the arctometatarsus. The evolutionary history of the arctometatarsus further highlights the presence of a phylogenetic constraint outside Coelurosauria, as this foot specialization is restricted to members of this group. Finally, our date estimation, based on compiled evolutionary patterns, demonstrates that these cursorial traits emerged during the mid-Cretaceous (93-120 Ma), suggesting selection on theropod locomotor performance throughout this interval.
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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 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| 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".