Evolving mineralogy of cheilostome bryozoans
Bibliographic record
Abstract
Abstract Cheilostomes dominate bryozoan faunas today and are the only order of bryozoans to have evolved aragonitic, calcitic, and bimineralic skeletons. New XRD analyses of 177 recent species and 34 Cretaceous–Eocene species are combined with published data to probe the mineralogical evolution of cheilostomes. This is undertaken with particular reference to the effects of the late Paleogene transition from calcite to aragonite seas believed to have been driven by the increasing Mg/Ca ratio in seawater. Aragonite was absent from all of the Cretaceous and Paleocene cheilostomes analyzed, even though most came from deposits preserving aragonitic mollusk shells, but was detected in four distantly related cheilostomes from the middle Eocene (Lutetian). Examples of cheilostomes preserved as partial molds, however, suggests that bimineralic species with aragonitic outer skeletal layers may have originated as early as the Maastrichtian. A strong latitudinal gradient was evident in cheilostome mineralogy, with the proportion of aragonitic and bimineralic recent species increasing towards the tropics. Unfortunately, relatively few low-latitude bryozoans have been described from the Cretaceous and Cenozoic fossil record, where aragonitic species are likely to be most numerous and may have their oldest occurrences. A combined database of cheilostome mineralogy shows aragonite to be widely distributed across Cheilostomata, occurring in numerous genera and families belonging to the three most diverse subgroups (Flustrina, Umbonulomorpha, and Lepraliomorpha) as well as one genus of Malacostegina. In spite of the lack of a robust phylogeny for cheilostomes, it is clear that aragonite has evolved independently on multiple occasions, the earliest acquisitions antedating the onset of aragonite seas, although apparently accelerating after this transition.
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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 | 0.003 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 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".