Cranial morphology of recumbirostrans (Lepospondyli) from the Permian of Kansas and Nebraska, and early morphological evolution inferred by micro-computed tomography
Bibliographic record
Abstract
‘Microsaurs’ (Lepospondyli) were a group of tetrapods whose fossil record spanned the Mississippian–Early Permian, and have sometimes been implicated in the origins of lissamphibians (especially the fossorial caecilians). Although common in the well-sampled Permian deposits of Texas and Oklahoma, little is known of conservative recumbirostran ‘microsaurs’ from more northerly localities (Kansas/Nebraska). Data on a new, well-preserved recumbirostran, Huskerpeton englehorni, gen. et sp. nov., from the Eskridge Formation, Nebraska, reveal affinities to the purported gymnarthrid ‘Euryodus’ bonneri (here moved to a new genus, Proxilodon) from the Speiser Formation, Kansas. High resolution micro-computed tomography reveals important endocranial data, including an ossified ‘supraoccipital’ that is usually absent in gymnarthrids, a dorsal sinus separating the synotic tectum from the dermal skull roof as in ostodolepids, ventral flanges of the frontals articulating directly with the ascending lamina of the sphenethmoid, and tall, ossified ‘pleurosphenoids,’ thereby providing useful comparison with morphologically derived recumbirostrans. A cladistic analysis of 60 taxa and 227 characters recovered a monophyletic clade of Huskerpeton, Proxilodon, and the recently described Tambaroter within a more inclusive clade that includes gymnarthrids and ostodolepids (both nested members of the Recumbirostra and putative outgroups to caecilians). Whereas other lepospondyls (i.e., lysorophians) are abundant in the region, the records of Huskerpeton and Proxilodon reveal that only two ‘microsaur’ genera are adequately known from the lowermost Permian of Kansas/Nebraska and demonstrate similarities between the Eskridge and Speiser faunas. Moreover, these forms may represent the ground plan from which more specialized fossorial forms (gymnarthrids and ostodolepids) evolved. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".