Deploy the proboscis!: Functional morphology and kinematics of a novel form of extreme jaw protrusion in the hingemouth, <i>Phractolaemus ansorgii</i> (Gonorynchiformes)
Bibliographic record
Abstract
Premaxillary protrusion and the performance advantages it confers are implicated in the success of diverse lineages of teleost fishes, such as Cypriniformes and Acanthomorpha. Although premaxillary protrusion has evolved independently at least five times within bony fishes, much of the functional work investigating this kinesis relates to mechanisms found only in these two clades. Few studies have characterized feeding mechanisms in less-diverse premaxilla-protruding lineages and fewer yet have investigated the distinctive anatomy underlying jaw kinesis in these lineages. Here, we integrated dissection, clearing and staining, histology, micro-CT, and high-speed videography to investigate an isolated and independent origin of jaw protrusion in the hingemouth, Phractolaemus ansorgii, which employs a complex arrangement of bones, musculature, and connective tissues to feed on benthic detritus via a deployable proboscis. Our goals were to provide an integrative account of the underlying architecture of P. ansorgii's feeding apparatus and to assess the functional consequences of this drastic deviation from the more typical teleost condition. Phractolaemus ansorgii's cranial anatomy is distinct from all other fishes in that its adducted lower jaw is caudally oriented, and it possesses a mouth at the terminal end of an elongated, tube-like proboscis that is unique in its lack of skeletal support from the oral jaws. Instead, its mouth is supported primarily by hyaline-cell cartilage and other rigid connective tissues, and features highly flexible lips that are covered in rows of keratinous unculi. Concomitant changes to the adductor musculature likely allow for the flexibility to protrude the mouth dorsally and ventrally as observed during different feeding behaviors, while the intrinsic compliance of the lips allows for more effective scraping of irregular surfaces. From our feeding videos, we find that P. ansorgii is capable of modulating the distance of protrusion, with maximum anterior protrusion exceeding 30% of head length. This represents a previously undescribed example of extreme jaw protrusion on par with many acanthomorph species. Protrusion is much slower in P. ansorgii-reaching an average speed of 2.74 cm/s-compared to acanthomorphs feeding on elusive prey or even benthivorous cypriniforms. However, this reorganization of cranial anatomy may reflect a greater need for dexterity to forage more precisely in multiple directions and on a wide variety of surface textures. Although this highly modified mechanism may have limited versatility over evolutionary timescales, it has persisted in solitude within Gonorynchiformes, representing a novel functional solution for benthic feeding in tropical West African rivers.
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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 | 0.000 | 0.000 |
| 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".