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 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 | 0.002 | 0.001 |
| 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 | 0.004 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".