Exceptionally-preserved late Cambrian fossils from the McKay Group (British Columbia, Canada) and the evolution of tagmosis in aglaspidid arthropods
Bibliographic record
Abstract
Documentation of non- or weakly biomineralizing animals that lived during the Furongian is essential for a comprehensive understanding of the diversification dynamics of metazoans during the early Palaeozoic. However, the fossil record of 'soft'-bodied metazoans is particularly scarce for this critical time interval, consisting of rare fossils found at a dozen or so localities worldwide. Here we report new occurrences of exceptional preservation in Furongian (Jiangshanian) strata of the McKay Group near Cranbrook, British Columbia, Canada. This locality had already yielded trilobites with phosphatised guts, with all specimens representing the same species and occurring within a 10-m-thick interval. Two stratigraphically higher horizons with soft-tissue preservation are reported herein; one has yielded a ctenophore and an aglaspidid arthropod, the other a trilobite with a phosphatised gut belonging to a different species than the previously described specimens. The ctenophore represents the first Furongian record of the phylum and the first reported occurrence of Burgess Shale-type preservation in the upper Cambrian of Laurentia. The aglaspidid belongs to a new species of 'Glypharthrus', and is atypical in having twelve trunk tergites and an anteriorly narrow 'tailspine'. These features suggest that the tailspine of aglaspidids evolved from the fusion of a twelfth trunk segment with the telson. They also confirm the vicissicaudatan affinities of these extinct arthropods. Compositional analyses suggest that aglaspidid cuticle was essentially organic with a thin biomineralised (apatitic) outer layer. The trilobite reveals previously unknown gut features, such as medial fusion of digestive glands, possibly related to enhanced capabilities for digestion, storage, or the assimilation of food. The new fossils demonstrate that conditions conducive to soft-tissue preservation repeatedly developed in the outer shelf environment represented by the Furongian strata near Cranbrook. Future exploration of the c. 600-m-thick, mudstone-dominated upper part of the section may result in more abundant discoveries of exceptional fossils.
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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 | 0.004 | 0.004 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".