Post-Glacial Hirnantian (Upper Ordovician) Bryozoans from Western Argentina: Implications for Survival and Extinction Patterns
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Bibliographic record
Abstract
Two bryozoan taxa occurring in the Hirnatian (Upper Ordovician) deposits in western Argentina document a first postglacial community associated with a mid-to high-latitude brachiopod assemblage, known as the typical Hirnantia fauna, in the Argentine Precordillera. Helopora fragilis Hall and an indeterminate phyloporinid occur within a thin but conspicuous shell bed that overlies diamictitic deposits from the lower member of the Don Braulio Formation. The abundance of well preserved specimens of bryozoans together with the dominance of suspension feeders suggests a mid-shelf setting (offshore transition) with an intermediate to low sedimentation rate, low turbidity, and nutrient-rich conditions. Hirnantian bryozoan assemblages identified from tropical and subtropical regions are rather rare, and this assemblage represents the first high-latitude Hirnantian record. The low diversity of bryozoans may be related to high-latitude location of Argentina during the Late Ordovician. Helopora Hall occurs mainly in Laurentia with several species occurring in the Katian and with a few Hirnatian occurrences in Gondwana. This broad distribution may imply that this genus had a broad environmental tolerance. It is one of the genera that successfully crossed the Ordovician/Silurian boundary. However, although this genus shows a post-extinction diversification and a more widespread distribution in Laurentia (with numerous species recorded in the Silurian and Devonian of Canada, Russia and China), it became extinct in Gondwana. We hypothesize that environmental conditions after the Ordovician/Silurian boundary may have prevented the settlement of bryozoans and caused the extinction of Helopora in the Argentine Precordillera.
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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 | 0.000 | 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) | 0.000 | 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 it