Evolution of the Amphibian Ear with Implications for Lissamphibian Phylogeny: Insight Gained from the Caecilian Inner Ear
Bibliographic record
Abstract
The inner ear is a complex structure consisting of the vestibular and auditory systems. Across vertebrates, morphological variation in the inner ear provides a source of homologous features (characters) that may aid in resolving phylogenetic relationships. The morphology of the inner ear in extant frogs and salamanders is well known, and has been extensively studied from functional perspectives. However, the ability of its form and features to shed light on the broader question of lissamphibian origins and relationships has not been as thoroughly explored. Herein we review the morphology of the inner ear of the least well-known lissamphibian group, the caecilians, and present three-dimensional reconstructions of otic capsule endocasts and of soft-tissue labyrinths. We use these data to explore previous statements about the structure of the caecilian inner ear and its evolutionary significance. The postulate that the periotic canal has a posterior path is corroborated, and the periotic sacs of each ear are observed to extend into the brain cavity, where they are applied to a fluid-filled compartment that is located ventral to the brain. These features are shared with frogs and salamanders. Additionally, it is hypothesized that the regression of two endorgans in caecilians is correlated with the secondary loss of the two middle ear auditory pathways, the tympanum–stapes and opercularis hearing pathway, suggesting that the lissamphibian-type ear is present, but in a derived state in caecilians. Identification of osteological correlates of this lissamphibian-type ear permits the interpretation of the evolution of this distinct ear type in the context of the three competing hypotheses of lissamphibian phylogeny. The distribution of traits is shown to be most parsimoniously explained when optimized onto the phylogenetic pattern that incorporates a monophyletic temnospondyl-derived Lissamphibia. This interpretation is consistent with a single origin of a lissamphibian-type tympanic ear. Therefore, characters of the ear seemingly provide synapomorphies that unite lissamphibians with amphibamid temnospondyls, potentially improving the resolution of concepts about the affinities of frogs, salamanders, and caecilians and clarifying issues of tetrapod ear evolution.
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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 | 0.000 | 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 | 0.000 | 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".