First report of paired ventral endites in a hurdiid radiodont
Bibliographic record
Abstract
Background: Radiodonta, large Palaeozoic nektonic predators, occupy a pivotal evolutionary position as stem-euarthropods and filled important ecological niches in early animal ecosystems. Analyses of the anatomy andphylogenetic affinity of these large nektonic animals have revealed the origins of the euarthropod compound eye andbiramous limb, and interpretations of their diverse feeding styles have placed various radiodont taxa as primaryconsumers and apex predators. Critical to our understanding of both radiodont evolution and ecology are the pairedfrontal appendages; however, the vast differences in frontal appendage morphology between and within differentradiodont families have made it difficult to identify the relative timings of character acquisitions for this body part.Results: Here we describe a new genus of hurdiid, Ursulinacaris, from the middle Cambrian (Miaolingian, Wuliuan) MountCap Formation (Northwest Territories, Canada) and Jangle Limestone (Nevada, USA). Ursulinacaris has the sameorganisation as other hurdiid frontal appendages, with elongate endites on the first five podomeres in the distalarticulated region and auxiliary spines on the distal margin of endites only. Unlike all other hurdiid genera, whichpossess a single row of elongated and blade-like ventral endites, this taxon uniquely bears paired slender endites.Conclusion: The blade-like endite morphology is shown to be a hurdiid autapomorphy. Two other frontal appendagecharacters known only in hurdiids, namely auxiliary spines on the distal margin of endites only, and elongate enditeson the first five podomeres in the distal articulated region only, predate this innovation.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".