Angular cartilage structure and variation in Neotropical freshwater stingrays (Chondrichthyes: Myliobatiformes: Potamotrygonidae), with comments on their function and evolution
Bibliographic record
Abstract
Abstract The various configurations of the jaws, anterior branchial arches and neurocranium provide some of the fundamental synapomorphies, distinguishing the major lineages of sharks, rays and ratfishes. For the Neotropical freshwater stingrays (family Potamotrygonidae), putatively unique skeletal elements, the angular cartilages, are intermediate between the hyomandibula and the lower jaw. These skeletal elements have been proposed as a synapomorphy for the potamotrygonids, but confidence in this character has been limited by poor sampling and taxonomic uncertainty, particularly regarding their ontogeny and homology. The morphology of the angular cartilages across the family is described, and the nomenclature of these structures is standardized. In addition, developmental and functional hypotheses for the origins of the angular cartilages are proposed. These cartilages, formed within the hyomandibular–Meckelian ligament, are suggested to be fibrocartilaginous in origin and aid in jaw kinesis. The angular cartilages are corroborated as a synapomorphy for Potamotrygonidae, although there is great variation within the family and similar structures have arisen independently in other extinct and extant batoid lineages. In potamotrygonines, the angular cartilages appear to have been lost in piscivorous Heliotrygon and Paratrygon, while additional angular cartilages were gained, typically one at a time, in some lineages of Potamotrygon.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 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) | 0.001 | 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".