EvoSheep – Origin and evolution of sheep breeds: 3D bone modelling to morphometrics investigation
EvoSheep is a multidisciplinary project on the origins and evolution of sheep breeds, involving archaeozoologists, epigraphists, bio-statisticians, and geneticists (Vila et al. 2021). The research focuses on the region of sheep domestication in Southwest Asia, specifically the Near East, to understand the onset of differentiation of early domestic sheep into multiple breeds. This research is based on the study of archaeological and modern sheep osteological data.
In order to understand the evolution of domestic sheep through time and space and to attempt to relate the past to the present, we investigate modern sheep breeds in a vast region extending from Eastern Africa to Iran.
One of the research topics of the Evosheep project is the identification of sheep diversity in the past through the tools available in geometric morphometrics methods (GMM). GMM is an approach that aims to analyse size and anatomical shape of biological forms according to their variations compared and analysed statistically (Cucchi et al. 2015). The objective of this research is to track sheep population history through the study of their skeletons from the beginning of domestication to the end of the Iron Age. To address these questions, this work follows two objectives:
- exploring biotic and abiotic factors affecting skeletal morphology from well-documented modern references;
- identifying characteristic morphological markers to document past phenotypic diversity.
For this purpose, my research is based on the analysis of postcranial bones from modern reference collections and archaeological sites. The modern collections included eleven sheep breeds and two wild sheep species from Turkey, Lebanon, Iran, Ethiopia and France. The Turkish domestic sheep corresponds to the Karagöz, Mandak and Kuyuruksuz breeds and was collected by Ingrid Beuls and Bea de Cupere (Beuls et al. 2000, Beuls 2004). The Lebanese sheep belongs to the Awassi breed. They were collected by Jwana Chahoud and colleagues between 2018 and 2019 (see post Chahoud and Vila 2021). The Iranian osteological collection assembled by Marjan Mashkour (Mashkour 2001, Mohaseb 2003, Mashkour et al. 2015) includes two domestic sheep breeds, Bakhtiari and Ziaran, and the wild species of Asiatic Mouflon (Ovis orientalis). The Ethiopian sheep collection includes six local breeds, Afar, Black Headed Somali, Bonga, Gumz, Menz and Washera. This collection was made by Emmanuelle Vila and her colleagues during the last four years (see post Vila and Amane 2022). Lastly, the French specimens correspond to Corsican mouflons (Ovis aries musimon) from the osteological heritage collections of the Muséum National d’Histoire Naturelle in Paris and the osteological collection of the Archéorient laboratory (UMR 5133) in Jalès collected during my PhD thesis (Vuillien 2020).
For each of these collections, we have much information on the animals (age, sex, phenotype) and their living environments (climate, geographical area, elevation). This allows us to evaluate objectively the contribution of each of these characteristics in the morphological evolution of domestic sheep. The archaeological collections come from about fifty faunal assemblages collected from froty-eight archaeological sites located in Mesopotamia, the Caucasus and the Iranian Plateau. These collections were carefully recovered from secure stratigraphic levels dating from the beginning of the Neolithic to the Iron Age.
The bones selected are the distal humerus, calcaneus and astragalus. These bones located in the appendicular limbs, participate in the flexion-extension movements of the elbow, for the humerus, and of the ankle, for the calcaneus and the astragalus. They have the three advantage of being diagnostic for taxonomic identification (Boessneck et al. 1964, Prummel and Frisch 1986, Clutton-Brock et al. 1990, Fernandez 2001, Salvagno and Albarella 2017), accurately recording biomechanical adaptations to environmental (Barr, 2014) and biological changes, and being relatively well preserved in archaeological contexts. Furthermore, these skeletal elements are already being examined in geometric morphometrics for other taxa, such as reindeer (Pelletier et al., 2020 et 2021), cattle (Cucchi et al. 2019), or wild boar and pigs (Harbers et al 2020a et 2020b, Neaux et al. 2022), as well as wild and domestic caprines (Haruda 2017, Pöllath et al. 2018 – 2019, Colominas et al. 2019, Haruda et al. 2019, Vuillien 2020).
To explore the morphological variations of these bones at the inter- and intra-specific level, we chose to collect the data from a 3D model. The use of 3D allows the study of topographic variations of specific bone regions from coordinated landmarks. Moreover, the choice of 3D imaging was particularly motivated by the temporary accessibility of modern and archaeological collections and by the desire to promote multidisciplinary investigations by archiving digital information and making it accessible to the scientific community. (available soon on the EvoSheep website).
3D models were acquired using the Artec Spider blue LED structured light scanner and the Artec Studio reconstruction software. This hardware was made available by the “2D and 3D Surveys, Modelling and Data Archiving” technical platform of the CEPAM laboratory (UMR 7264, CNRS, UCA) during my doctoral thesis (Vuillien, 2020; see post Vuillien 2017) and, recently, by the Bioarchaeology Imaging Platform of the AASPE laboratory (UMR 7209, CNRS, MNHN). This type of surface scanner has the triple advantage of being portable, of ensuring the digitization of small parts and of being accurate in the restitution of complex shapes.
The acquisition protocol consists of mounting the scanner on a photographic tripod and placing the bone on a rotating table in order to ensure a rapid and uniform scanning face by face (Fig. 1). Each face is scanned, cleaned, aligned and then meshed. The model is reconstructed at a resolution of 0.1 mm from the geometry of the latter. The mesh is composed of n triangles representing the surface of the object. Then, the model is textured and then exported a minima in “ply” and “obj” formats following the recommendations of CINES (Vergnieux et al., 2017) (Fig. 2). The texture is a two-dimensional image represented as a pixel grid. A pixel in the texture, called a texel, corresponds to a point in the three-dimensional object. The texel’s colour produces the color of the object point.
Today, the dataset at our disposal includes 916 3D models of which 366 are from modern domestic sheep and Asiatic mouflon and 550 from archaeological specimens, i.e. 335 distal humeri, 127 calcaneus and 454 astragalus. For the studies in geometric morphometrics, we have preferred the digitization of modern individuals over one year old. For the archaeological specimens, whenever possible, we chose bone elements with fused epiphyses (distal epiphysis for the humerus and apex for the calcaneus) and with few/no visual modifications of the bone structure and volume (Fig. 3).
3D morphometric investigation: let’s do it!
Protocols and results on the collections will be published soon!
EvoSheep was funded by the French National Research Agency (ANR). This work was funded by EvoSheep project and the Centre National de la Recherche Scientifique (CNRS). I am thankful to all the archaeologists, archaeozoologists, curators and institutions who provided access to the modern and archaeological collections. Particular thanks are due to Jwana Chahoud (Univ. Lyon 2-Archéorient UMR 5133 and Lebanese University), Bea de Cupere (Royal Belgian Institute of Natural Sciences), Agraw Amane (Addis Ababa University & ILRI), Rémi Berthon and Joséphine Lesur, Adeline Vautrin, Azadeh Mohaseb (AASPE UMR 7209, MNHN, CNRS), Moussab Albesso and Daniel Helmer (Univ. Lyon 2-Archéorient UMR 5133), Hossein Davoudi and Homa Fathi, Sarieh Amiri, Roya Khazaeli, Haeedeh Laleh (Bioarchaeology Laboratory, Central Laboratory, University of Tehran). Emmanuelle Vila (Univ. Lyon 2-Archéorient UMR 5133), Marjan Mashkour (AASPE UMR 7209, MNHN, CNRS), Thomas Cucchi (AASPE UMR 7209, MNHN, CNRS) and Lionel Gourichon (UCA – CEPAM UMR 7264, CNRS) supervised this work to whom I am grateful.
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Manon Vuillien est postdoctorante au CNRS, archéozoologue. Elle est membre de l’UMR 7209 Archéozoologie – Archéobotanique : Sociétés, Pratiques et Environnements (AASPE), MNHN, Paris, France.