Cheek tooth morphology and ancient mitochondrial DNA of late Pleistocene horses from the western interior of North America: Implications for the taxonomy of North American Late Pleistocene Equus.
Authors: Barrón-Ortiz Christina I, Rodrigues Antonia T, Theodor Jessica M, Kooyman Brian P, Yang Dongya Y, Speller Camilla F
Journal: PloS one
Summary
# Editorial Summary Late Pleistocene North America supported multiple horse species whose taxonomic relationships have remained contested, partly owing to limited morphological comparison and few molecular data from western populations. Barróń-Ortiz and colleagues analysed cheek tooth morphology using geometric morphometrics alongside ancient mitochondrial DNA from specimens across the Western Interior, establishing a robust framework for species identification across the region prior to end-Pleistocene extinction. Two primary taxa were confirmed—the caballine *Equus ferus* and the non-caballine *E. conversidens*—with phylogenetic analysis of mtDNA and premolar morphometry clearly separating these groups, whilst a third non-caballine species, *E. cedralensis*, was identified solely from southern localities through dental morphology. Notably, caballine specimens from Bluefish Caves in Yukon Territory displayed statistically distinct occlusal enamel patterns compared to southern populations, suggesting either adaptive responses to Arctic conditions or genetic and geographic isolation warranting further investigation. For equine professionals engaged with fossil material or evolutionary discussions, this work provides reliable morphological benchmarks for species differentiation and highlights how integrated morphological and molecular approaches can resolve long-standing taxonomic uncertainties in extinct equid populations.
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Practical Takeaways
- •This paleontological study has no direct clinical or practical application to contemporary equine practice or farriery
- •The taxonomic clarification of extinct North American Pleistocene horse species is primarily relevant to paleontologists and evolutionary biologists
- •Understanding ancient equine diversity and geographic variation contributes only indirectly to knowledge of modern domestic horse anatomy and physiology
Key Findings
- •Two main Equus species identified in late Pleistocene Western North America: caballine (Equus ferus) and non-caballine (E. conversidens), with a third non-caballine species (E. cedralensis) recognized in southern localities
- •Separation between caballine and non-caballine species confirmed through both geometric morphometric analysis of premolars and Bayesian phylogenetic analysis of ancient mtDNA
- •Geographic variation in occlusal enamel patterns observed in caballine specimens from Bluefish Caves, Yukon Territory compared to other regions, suggesting possible ecomorphological variation or geographic isolation