Sr‐O‐C isotope signatures reveal herbivore niche‐partitioning in a Cretaceous ecosystem
Bibliographic record
Abstract
Abstract Stable and radiogenic isotopes represent powerful tools for reconstructing ecological and environmental patterns in ancient ecosystems. The Cretaceous of North America preserves a diverse record of fossil vertebrates well‐suited to analysis using these proxies, contained within many well‐sampled and stratigraphically well‐characterized intervals. Multiple hypotheses have been offered to explain the diverse assemblages of megaherbivores that co‐occurred in the relatively restricted available landmass here, including various forms of niche‐partitioning related to habitat preference, dietary specialization and feeding height stratification. Here we analyse the 87Sr/86Sr, δ13C and δ18O of bioapatite samples obtained from a range of herbivores, faunivores and endemic taxa, from a spatiotemporally‐constrained and intensively‐sampled site in the upper Oldman Formation, to test if megaherbivores partitioned their niches based on spatial patterns of occupation and resource‐use. We also compare measured strontium values to regional 87Sr/86Sr data to assess biogeographical range sizes, habitat breadth and migration potential. We find that hadrosaurs had broad ranges, whereas ankylosaurs and ceratopsids were more spatially restricted. The 87Sr/86Sr ranges of hadrosaurs are much wider and do not overlap with those of other ornithischians, potentially related to dietary differences driven by a combination of feeding height‐stratification and habitat breadth differences. Ankylosaurs and ceratopsids overlapped extensively in 87Sr/86Sr, δ13C and δ18O, indicating overlap in the same habitats and intake of similar resources, and suggesting more complex spatiotemporal variation in resource‐use patterns, fine‐scale dietary differences, and/or sufficient resource‐availability to reduce the degree of competition given this theoretical niche overlap. Additional analyses integrating ecomorphological proxies may elucidate these patterns further.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".