Knowledge about the origin and evolutionary history of the bison has been improved recently owing to several genomic and paleogenomic studies published in the last two years, which elucidated large parts of the evolution of bison populations during the Upper Pleistocene and Holocene in Eurasia. The produced data, however, were interpreted in contradicting manners. Here, we have gathered, reanalyzed and compared previously published or unpublished morphometric and genetic data that have not yet been integrated and that we synthesize in a unified framework. In particular, we re-estimate dates of divergence of mitogenome lineages based on an extended dataset comprising 81 complete ancient bison mitogenomes and we revisit putative gene flow between the Bos and Bison genera based on comparative analyses of ancient and modern bison genomes, thereby questioning published conclusions. Morphometric analyses taking into account sexual dimorphism invalidate a previous claim that Bison schoetensacki was present in France during the Late Pleistocene. Both morphometric and genome analyses reveal that Eurasian bison belonging to different Bison priscus and Bison bonasus lineages maintained parallel evolutionary paths with gene flow during a long period of incomplete speciation that ceased only upon the migration of B. priscus to the American continent establishing the American bison lineage. Our nuclear genome analysis of the evolutionary history of B. bonasus allows us to reject the previous hypothesis that it is a hybrid of B. priscus and Bos primigenius. Based on present-day behavioral studies of European and American bison, we propose that apparently conflicting lines of evidence can be reconciled by positing that female bison drove the specialization of bison populations to different ecological niches while male bison drove regular homogenizing genetic exchanges between populations.

Equus is a very sensitive genus which has expanded over a large area and lived in Europe despite the climatic instability of the Pleistocene. Its persistence and abundance are helpful in understanding and describing environmental and climatic regional parameters. In this study, we present the result of dental mesowear and microwear analysis and post-cranial skeleton biometry on Equus populations located in two regions in the South of France from ten sites, corresponding to twelve assemblages dated from MIS 12 to MIS 5. The areas refer to two major climatic zones: the oceanic or subcontinental climate for the South West of France, and the Mediterranean for the South East. The first objective of this study is to integrate and compare biometric data, dental wear, and other already-published environmental proxies. The goal is to discuss the validity of horse body shape adaptations on a small geographical scale. The second objective is to describe the impact of environmental features on the horse population through time in the two regions. We observe that the Equus diet was quite diverse, according to microwear analysis which shows adaptations according to seasonal variations. However, they remained mostly grazers over a long period of time. Estimated body mass of Equus in the localities studied here varies from a mean of 468 up to a mean of 570 kg, but these variations failed to be correlated with the diet, the climatic period, or the geographical position of the horse population, probably because of the sample size or the restricted time-span or geographical scale. However, the conformation of the metapodials and the width of the third phalanges may have been linked with environmental and behavioural parameters. The width of the third phalange may be correlated with the recurrence of the snow cover, while the robustness of the metapodial co-occurs with a humid climate. Also, diet may influence the conformation of the bones, since the tall and slender horses seem to be preferentially grazers all year long and seasonally browser horses are tall and robust. Seasonally mixed-feeder horses, all coming from the Mediterranean area, were found to be smaller, perhaps in relation to a less productive environment. The correspondence of the dietary and morphometrical data could suggest high pressure on the horse population, which caused rapid body adaptation. Thus, the combination of these different proxies allows us to suggest more accurate large mammal paleoenvironmental reconstructions.

The morphometric adaptations and the phyletic evolution of the Equus genus during the Quaternary are still the focus of many studies. Several forms (species/subspecies) of Middle and Upper Pleistocene horses have been described in Europe but their spatio-temporal variations, in relation to the environment and the climate require further clarification. This is the case in particular for a typical Middle Pleistocene form: Equus mosbachensis ssp. In this paper, we present combined morphological and ecometric observations based on the upper teeth from three subspecies of this form from five sites: Camps-de-Peyre (E. m. campdepeyri), La Micoque (E. m. micoquii), Lunel-Viel I and Lunel-Viel IV (Equus m. palustris) and Igue des Rameaux (E. mosbachensis ssp.). The understanding of the specific characteristics of this taxon should enable us to better define the occupied habitat and environment. This preliminary study shows the importance of the adaptive capacities of Equus mosbachensis and the pertinence of combined paleontological and ecometric studies for enhancing our understanding of the ecology and the evolution of fossil ungulates. In addition, some authors have postulated that the length of the protocone is correlated to a diet with a high grass content. Although this tendency may have existed during the Quaternary, our study shows, on a smaller chronological scale, that there is no correlation between this measurement and horse diet and paleoenvironment.