Interplay between evolutionary history, morphological constraints and functional adaptations in the primate cochlea
Bibliographic record
Abstract
How the intricate mammalian cochlea evolved, and its functional implications, remain only partly understood. Here, we explore cochlear morphology across 101 extant and fossil species of the mammalian grand order Euarchonta using micro-computed tomography, three-dimensional geometric morphometrics and phylogenetic comparative analyses. We find substantial shape variation across taxa, likely driven by an interplay between evolutionary history, morphological constraints and potentially functional demands, although these remain difficult to interpret. Evolutionary models suggest the rate of cochlear shape evolution was heterogeneous, with some lineages showing particularly high rates, likely linked with adaptive selection pressures (e.g. tarsiers, Cercopithecus ). Ancestral state reconstructions reveal lemuriforms retain the ancestral strepsirrhine cochlear shape—conical with around 2½ turns—while lorisiforms exhibit a derived cylindrical cochlea with increased coiling. The highly coiled cochlea of tarsiers reflects cranial constraints and functional demands, particularly for high-frequency hearing. In anthropoids, platyrrhines nest within catarrhine variation. Among the latter, cercopithecins trend towards increased coiling, whereas colobines and hominoids retain less coiled shapes. Finally, while body size has little effect on cochlear shape, its interaction with cochlear length predicts the number of turns, supporting the theory that cochlear coiling enabled the development of a longer basilar membrane within a small petrous space.
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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 | 0.001 |
| 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 | 0.002 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| 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".