Combining Morphology and Palaeogenomics to understand the Status and Contribution of Mules to Roman Equine Populations in Austria and Germany.

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In evolutionary and cultural studies, interspecies hybridisation is a relevant topic. In this respect, humans have been crossbreeding wild and domestic members of the family Equidae since millennia, as illustrated by archaeological, iconographic and written sources. In focus of this study is the mule, the cross between the male domestic donkey and the mare. Being more effective than either of the parental stock, elicited by the so-called heterosis effect, mules were particularly valued as labour animals and according to Classical sources bred in numbers. However, identifying mules (and other equid hybrids) in archaeofaunal assemblages based solely on dental and osteomorphological features is problematic and prone to considerable inter-observer variation. Consequently, application of traditional morphological methods might not be very efficient to specifying adequately the role of mules in ancient cultures.This study aims at elucidating local breeding practices and the contribution of mules to the equid populations exploited in southeastern Germany and Austria in pre-Roman and Roman times. It will apply a multidisciplinary approach combining standard morphology with Geometric Morphometrics (GMM) and ancient DNA analysis in order testing several hypotheses, namely that (H1) the mule represents a marker for the process of Romanization in the Provinces Raetia (Germany), Noricum and Upper Pannonia (Austria), (H2) north of the Alpine divide hybridization between male donkeys (jackass) and female horses (mare) was not practiced, implying that animals had to be imported from regions south of the Alps where cross-breeding was already established, and (H3) the high demand for horses in Roman military service in Raetia not only necessitated imports from elsewhere but involved breeding efforts with local horse lineages descending from pre-Roman local populations. From a methodological viewpoint our project expects establishing a reliable genetic and GMM pipeline for tracing systematically F1-hybrids in equine archaeological assemblages, thus enabling to validate identifications based on standard morphological analyses. By comparing the results of the different approaches it will also be possible to quantify the degree of accuracy for recognizing hybrids in cases where only standard morphological analyses can be performed. In sum, we expect that the combined approach proposed here will open up additional venues to address the hitherto underestimated role of equine hybrids in past societies whilst significantly enhancing our knowledge of the cultural, economic and military history of the mule in the Roman Empire north of Alps.