The Late Pleistocene Extinction in North America: An Investigation of Horse and Bison Fossil Material and Its Implication for Nutritional Extinction Models
Bibliographic record
Abstract
Approximately 50,000 – 11,000 years ago many species around the world became extinct or were extirpated at a continental scale. The causes of the late Pleistocene extinctions have been extensively debated and are poorly understood. This dissertation focuses on testing two nutritional extinction models (coevolutionary disequilibrium and mosaic-nutrient models) through the study of dental wear and enamel hypoplasia of equid and bison specimens from the Western Interior of North America. In order to undertake this task it was first necessary to determine the number of equid species that inhabited this region during the late Pleistocene. Notable findings of this research include the identification of four equid taxa based on molecular and morphometric analyses of the cheek teeth. Two non-caballine species and two caballine subspecies were identified which, pending further study of North American Pleistocene Equus, are referred as: Equus cedralensis, E. conversidens (which corresponds to the New World stilt-legged group of previous molecular analyses), E. ferus scotti, and E. ferus lambei. The separation into caballine and non-caballine equids was revealed in both the Bayesian phylogenetic analysis of mitochondrial ancient DNA and the geometric morphometric analyses of the upper and lower premolars. Investigation of the dental wear (microwear and mesowear) of the equid and bison samples studied yielded results which are consistent with predictions established for the coevolutionary disequilibrium extinction model, but not for the mosaic-nutrient model. These ungulate species show statistically different dental wear patterns, suggesting dietary resource partitioning, prior to the postglacial, but not during this time interval in accordance to predictions of the coevolutionary disequilibrium model. In addition to changes in diet, these ungulates, specifically the equid species, show increased levels of enamel hypoplasia during the postglacial indicating higher levels of systemic stress, a result which is consistent with the models tested as well as other climate-based extinction models that have been proposed. The extent to which the increase in systemic stress was detrimental to equid populations remains to be further investigated, but it is suggestive that environmental changes might have played an important role in the extinction of equids and perhaps other Pleistocene ungulates.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".