<scp>P</scp>alaeocene–<scp>E</scp>ocene evolution of beta diversity among ungulate mammals in <scp>N</scp>orth <scp>A</scp>merica
Bibliographic record
Abstract
Abstract Aim The Palaeocene–late Eocene transition in North America marks a critical interval in the evolution and diversification of land mammals, including adaptive radiation in the Palaeocene, and repeated waves of immigration over habitat bridges at the Palaeocene–Eocene boundary. We investigate the fossil record of ungulate mammals over this period to understand the effects of immigration and faunal exchange on local (alpha), regional (gamma) and between‐site (beta) diversity. Location North America. Methods We use Palaeocene and Eocene records of North American ungulate mammals taken from the Paleobiology Database (PBDB), and calculate beta diversity among families and genera within the seven stages of the Cenozoic. We reconstruct geographic ranges sizes for studied taxa, and test trends in these ranges against null models used to control for sampling biases. Finally, we use Mantel tests to quantify the relationship between geographic distance and faunal dissimilarity within each time slice, in order to visualize changes in the spatial complexity of mammal communities. Results Gamma diversity increases over the studied interval, with varying contributions from alpha and beta diversity. Beta diversity increases from the Palaeocene to Eocene, reflected in decreasing range size and increased correlation between reconstructed distance and faunal similarity. Increase in beta diversity over the Palaeocene–Eocene transition is driven by smaller geographic ranges among putatively invasive ‘immigrant’ and secondarily endemic taxa; range contraction among these groups in the middle–late Eocene leads to a Bartonian peak in beta diversity. Main conclusions High gamma diversity in the Eocene was driven by high beta diversity rather than alpha diversity, indicating that range contraction in both immigrant and secondarily endemic taxa restructured the spatial organization of mammal communities. These parallel trends suggest that factors such as tectonic uplift or climate change were responsible, as opposed to ecological differences. Increase in beta diversity over the Palaeocene–Eocene boundary suggests that over longer time‐scales, mass immigration events can lead to greater overall richness and greater heterogeneity, rather than homogeneity, within regional assemblages.
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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 | 0.001 |
| 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".