Evolution, Paleoecology, and Paleobiogeography of the Late Ordovician Brachiopod Fauna of Laurentia
Bibliographic record
Abstract
During the early Katian (Late Ordovician), the North American craton was being inundated due to a major eustatic sea level rise and regional subsidence associated with the ongoing Taconic orogeny. The Trentonian brachiopod fauna, as a dominant group of the marine shelly benthos at that time, evolved and invaded the expanding epicontinental seas.\nThree Trentonian brachiopod lineages were studied to trace their evolution. The Rostricellula-Rhynchotrema-Hiscobeccus lineage was characterized by an increase in shell size, globosity, and frilled lamellae, with Hiscobeccus becoming a prominent component of the Late Ordovician epicontinental brachiopod fauna.\nParastrophina is a widely reported but non-dominant taxon of the Trentonian brachiopod fauna in eastern North America. This study clarified details of the internal structures of the type species, P. hemiplicata, and quantified the high degree of intraspecific variability, particularly the development of ribs, fold, and sulcus. This has led to the recognition of Parastrophina tarimensis from northwest China as a new species.\nPlectorthis is another key taxa of the Trentonian fauna, previously reported from several tectonic paleoplates. By examining the type species, P. plicatella, from the Cincinnati area in this study, the diagnostic characters of the genus were defined, which provided a basis for evaluating the North American and global distribution and diversity of this genus and a more accurate paleobiogeographic analysis.\nMultivariate analyses of the Trentonian brachiopod collections from Manitoulin Island and the Lake Simcoe area in Ontario, in conjunction with other Trentonian faunas from North America, demonstrated that during the early stage of the Late Ordovician (early Katian) sea level rise and marine inundation of the continental interior, the epicontinental sea brachiopod fauna began to separate from the older pericratonic faunas. In Ontario, this is reflected by the brachiopod fauna of Lake Simcoe being more closely related to the Scoto-Appalachian fauna, and that of Manitoulin Island most similar to those in the intracratonic basins (e.g. Minnesota).
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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 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".