Data from: A Burgess Shale mandibulate arthropod with a pygidium – a case of convergent evolution
Bibliographic record
Abstract
Cambrian ‘bivalved’ arthropods are a polyphyletic group of carapace-bearing arthropods which include stem euarthropods, stem mandibulates and crustaceans. Here, we describe Pakucaris apatis gen et. sp. nov. a new ‘bivalved’ mandibulate from the middle Cambrian (Wuliuan Stage) Burgess Shale (Marble Canyon, Kootenay National Park, British Columbia, Canada). Two morphotypes of this small arthropod (11.6–26.6 mm long) are recognized, differing mainly in their sizes and number of segments, possibly reflecting sexual dimorphism or different anamorphic stages. The carapace presents a dorsal crest extending anteriorly into a small recurved rostrum and two antero-lateral processes. Around 20% of the posteriormost body segments and limbs are covered by a large spine-bearing shield. The head bears a pair of eyes, a possible pair of unsegmented appendicular projections and two pairs of segmented appendages. The thorax is multisegmented, homonomous, with weakly sclerotized segments bearing biramous limbs, composed of a stenopodous endopod with c. 20 podomeres and a paddle-shaped exopod. Pakucaris is interpreted as a nektobenthic suspension feeder. A Bayesian phylogenetic analysis implies a position within Hymenocarina as stem mandibulates. The posterior shield is regarded as a pygidium, and represents a case of morpho-functional convergent evolution between a mandibulate, artiopodans and mollisoniids. Alternatively, the growing number of known pygidium-bearing arthropods may hint at a common developmental pattern across early arthropod evolution. This study not only increases our understanding of the early evolution of mandibulates but also illustrates a unique case of early evolutionary convergence during the Cambrian Explosion.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.004 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.077 | 0.048 |
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".