The homologies and evolutionary reduction of the pelvis and hindlimbs in snakes, with the first report of ossified pelvic vestiges in an anomalepidid (Liotyphlops beui)
Bibliographic record
Abstract
Abstract We report the first example of ossified pelvic vestiges in an anomalepidid snake, Liotyplophs beui, and provide a review of the diversity of limb and pelvic elements within Serpentes. We trace the evolution, homology and reduction of the pelvic elements and hindlimbs from the oldest known snakes through to living forms. Evolutionary analysis of the pelvic and limb data shows that the most recent common ancestor of all living snakes (Serpentes) most probably retained all three pelvic elements and rudimentary hindlimbs (femoral spurs). Subsequently, there have been multiple losses of ossified pelvic and hindlimb elements and regaining of ossified pelvic elements. Reduction of the pelvis has followed different routes in the two primary groups of living snakes (scolecophidians and alethinophidians). The single remaining rod-like element in some scolecophidians is the ischium, whereas the single remaining rod-like element in many basal alethinophidians is the pubis. Notably, many basal alethinophidians share a distinctive configuration of cloacal spur (claw), femur and a sizeable pubis, which is likely to be related functionally to the widespread use of the hindlimbs in mating and courtship, rather than the usual representation of the bones as non-functional vestiges.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".