Comparative anatomy of the skull of South American camelids: A contribution to their taxonomical identification

Abstract

South American camelids (Lamini tribe) are represented by two genera and four species. Here we studied the skull anatomy of three of them, Lama glama, Lama guanicoe and Vicugna vicugna. The coexistence of these species in wide sectors of their distribution and the osteological homogeneity of these camelids constitute important factors that limit or even preclude identification at species level. This is particularly true in paleontological and archaeological contexts in which bones are the only elements to analyze, and complete or fragmentary remains are potentially recorded. Although some contributions dealing with interspecific differentiation of camelids are available currently, the clear distinction between these species through osteological remains is still a pending issue. The aim of this study was to find osteological characters that facilitate the determination of the analyzed species. For this, we analyzed a final sample comprised mainly adult specimens of 11 guanacos, 9 llamas and 18 vicuñas. We described and compared a diverse set of qualitative and quantitative osteological features of the skull, including foramina, processes, muscular scars, and other features of the cranium and mandible. The set of qualitative features included eight observations on the cranium and four on the mandible. The set of quantitative features included eight linear variables on the cranium and two on the mandible. We performed a Partial Least Squares Discriminant Analysis (PLS-DA) based on both qualitative and quantitative variables in order to differentiate camelids species. The best results were obtained when both types of variables were included in the analysis. The most robust characters for interspecific discrimination are those related to the muzzle, the mastoid foramen, the paraoccipital process, the lower incisors and the coronoid and condylar processes of the mandible. The morpho-functional meanings of some of these traits are discussed. This study can be considered as a contribution to future systematic studies and as a basic tool to carry out specific assignment of camelids through complete or partial remains in archaeological and paleontological contexts.