β‐diversity fluctuations in Early–Mid Ordovician brachiopod communities of South China
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Bibliographic record
Abstract
Abstract Lower to Middle Ordovician transitional strata ( Acrograptus filiformis Biozone to Exigraptus clavus Biozone) of the Upper Yangtze Platform contain rich and diverse brachiopods, particularly in the Daguanshan Formation of Sichuan Province, the Meitan Formation of Guizhou Province, and the Yingpan Formation of Houping, Chongqing City. On the basis of multivariate analyses of 207 samples (about 15 000 brachiopod specimens) and 61 species from these strata, 23 brachiopod‐dominated communities and associations are delineated through six graptolitic biozones ( Acrograptus filiformis to Exigraptus clavus biozones). The disparity of brachiopod associations or β‐diversity, as measured by the number of contemporaneous associations across variable ecological settings, was low in the A. filiformis Biozone and increased through the overlying graptolitic biozones to reach an acme in the Azygograptus suecisus and Expansograptus hirundo biozones, where as many as nine different brachiopod associations thrived in mid‐shelf and also established in inner‐ and outer‐shelf environments. Despite a sharp increase in α‐diversity within the Didymograptellus eobifidus Biozone, β‐diversity remained relatively low, with only three distinct brachiopod communities. The diversity of brachiopod associations suffered an abrupt drop in the E. clavus Biozone, as a result of a major faunal turnover event, with only a single Metorthis Community present in an upper mid‐shelf setting. Temporally, brachiopod associations appear to be most stable in mid‐shelf settings, with the Paralenorthis , Sinorthis , Desmorthis , and Euorthisina communities having a relatively high α‐diversity and lasting through two to five graptolitic biozones. In both species composition and temporal duration, the brachiopod associations at the shallow‐ (BA1 to upper BA2) and deep‐shelf (BA4) settings are unstable, characterized by low α‐diversity and rapid vertical changes. This study implies that, during the Early and Mid Ordovician, brachiopod communities already attained a high level of organization in mid‐shelf settings, but remained poorly established in high‐stress environments of very shallow or very deep shelf settings. Copyright © 2006 John Wiley & Sons, Ltd.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 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)
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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 it