New information on<i>Lethiscus stocki</i>(Tetrapoda: Lepospondyli: Aistopoda) from high-resolution computed tomography and a phylogenetic analysis of Aistopoda
Bibliographic record
Abstract
High-resolution computed tomography provides an alternative to serial sectioning and other destructive techniques of studying fossils (data available at http://www.DigiMorph.org). This technology was used to study the oldest aistopod Lethiscus stocki. The fossil is found to have approximately 30 closely spaced teeth on its maxilla and dentary, a short vomer, a palatine running nearly the entire length of the maxilla that is toothed at least posteriorly, and a choana that is located at the premaxillamaxilla suture. It has a lower jaw with a high articlular facet for the quadrate condyle; a lateral fossa for the adductor musculature, superficially similar to the mammalian masseteric fossa; and a sutural pattern that closely resembles that of Oestocephalus. Previously reported pectoral elements are not evident in the scans and may be best interpreted as fractures on the surface of the nodule associated with sedimentary inclusions. Relationships among all relatively complete aistopods were analyzed using parsimony. Two most parsimonious trees were found, differing in the arrangement of the outgroup taxa. Phlegethontia and Pseudophlegethontia are found to be sister taxa to Coloraderpeton and Oestocephalus, with Ophiderpeton and Lethiscus placed as successively more distant taxa. This topology renders Ophiderpetontidae, as previously conceived, paraphyletic. Lethiscus is confirmed to be the most basal aistopod. A new classification of Aistopoda is presented. This study shows that the palatoquadrate of higher aistopods is derived in-group, which is consistent with the trends in aistopods of peramorphosis in the endochondral skeleton and paedomorphosis in the dermal skeleton.
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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 | 0.004 | 0.003 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.013 | 0.002 |
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".