Bajocian (middle Jurassic) Ammonitina of New Zealand
Bibliographic record
Abstract
Abstract A relatively rich, previously unknown fauna of Ammonitina is described from the Bajocian of southwest Auckland. The great majority are Sphaeroceratidae. The Chondroceras fauna has yielded C. orbignyanum and C. (Defonticeras) cf. oblatum, clearly indicating the Humphriesianum Chron. Also associated is the bivalve index Retroceramus inconditus. The superjacent fauna of Waikatoceratinae (n. subfam.) is almost exclusively endemic to New Zealand, with Waikatoceras crassum, W. hudsoni, Opuatia circularis, O. inflata, and O. challinori n. genn. et spp. Accessory taxa include Chondroceras cf. orbignyanum, and Toxamblyites aff. densicostatus, previously known only from the upper Lower Bajocian of Europe and North Africa. However, stratigraphic evidence together with the bivalve index Retroceramus marwicki clearly date the Waikatoceratinae fauna as mostly post‐Humphriesianum Chron (i.e., early Late Bajocian). The presence of Toxamblyites in this fauna suggests that its range was one chron longer in the Southwest Pacific than in Eurafrica—unless the fragmented specimens were reworked, which is considered unlikely. Relatively rare and often immature phylloceratids and lissoceratids are also associated. Other single finds of Middle Jurassic Ammonitina from other New Zealand regions are also discussed. Other stratigraphically important taxa include the bivalve Meleagrinella n. sp. and the belemnite Hibolithes catlinensis. The boundary between the Middle and Upper Temaikan regional substages can be defined by the first occurrence of either Retroceramus marwicki or of Waikatoceratinae; both boundaries lie in the Humphriesianum Chron. The bivalve index is widespread, permitting inter‐regional correlation, whereas the ammonite index allows reasonably precise dating.
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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) | 0.003 | 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".