The first pachycephalosaurid from the Late Cretaceous Two Medicine Formation: effects of the Western Interior Seaway on North American pachycephalosaurid evolution
Bibliographic record
Abstract
Abstract During the latest Cretaceous, western North America experienced several regressive and transgressive cycles of the Western Interior Seaway (WIS). Closely related, time-successive taxa of tyrannosaurids, ceratopsids, hadrosaurids, and pachycephalosaurids have been proposed to have evolved via anagenesis driven by habitat area fluctuations related to sea level change. Previous examinations into these anagenetic hypotheses have resulted in equivocal results. However, evolution related to this WIS hypothesis has yet to be tested for Pachycephalosauria. Originally, it was hypothesized that an undescribed taxon from the Two Medicine Formation constituted an anagenetic intermediate between the Campanian Stegoceras validum and the Maastrichtian Pachycephalosaurus wyomingensis. Here we describe this Two Medicine Formation pachycephalosaurid and test the proposed anagenetic lineage. This taxon is the first pachycephalosaurid from the Two Medicine Formation, and the massive frontoparietal dome indicates that it was the third largest North American pachycephalosaurid. Phylogenetic analyses recover this new taxon distant from both Stegoceras and Pachycephalosaurus; thus, refuting the hypothesis that this taxon constitutes any part of an ancestor–descent series between Stegoceras and Pachycephalosaurus. However, the new taxon not only increases understanding of pachycephalosaurid morphology and diversity, but shows that this clade contained relatively large body-sized taxa as early as the Middle Campanian.
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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 | 0.001 |
| 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".