Exploring Biological and Ecological Components of Sheep Astragalus Size and Shape Variation Using 3D Geometric Morphometrics: Towards A Bioarchaeological Proxy

Abstract

One of the key challenges in the archaeology of sheep domestication is reconstructing the complex history of environmental and anthropogenic transformations undergone by sheep since the beginning of the domestication process of their wild ancestors. In recent years, GMM studies of sheep astragalus bones have contributed to our understanding of morphological differences between wild and domestic caprine species. However, the respective influences of biological and ecological factors on astragalus morphological variations in sheep remain poorly documented. This limitation hinders a comprehensive understanding of its biosystematic resolution and, consequently, its use as a proxy in archaeological contexts to investigate early selective breeding and the emergence of sheep breeds in Southwest Asia. This paper presents the results of a morphological study of 96 astragali using 3D geometric morphometrics, focusing primarily on modern Eurasian and African sheep breeds and landraces. The study is based on a well-documented comparative collection encompassing phenotypical traits (breed, sex, age, presence/absence of horns, coat and tail type, weight, body length); ecological characteristics (climate, geography, environment, elevation, topography); and breeding strategies (mobility). The results demonstrate that the 3D astragalus morphological pattern is a reliable marker for distinguishing one sheep breed from another. They suggest that astragalus morphology is only slightly influenced by phenotypic markers. The study further explores the effects of environmental and climatic factors on phenotypic variation and highlights the potential of the astragalus as an ecomorphological marker. Finally, the current limitations in interpreting the relationship between astragalus morphological variation and mobility strategies in archaeological contexts are discussed.