Shape and size variations in the cranium of elephant-shrews: a morphometric contribution to a phylogenetic debate

A geometric morphometric analysis was carried out on the crania of 13 species of elephant-shrews (Macroscelidea), a group of African mammals whose phylogeny is still debated. The material examined consisted of 313 crania and included all the genera of Macroscelididae, the unique family recognized by taxonomists. The results obtained from the analysis of the cranium shape and size, either from dorsal or lateral view, were very similar. The first one appeared more reliable because of the higher number of intersection points fixed between the cranial sutures. All the cranial features that distinguished the genus Rhynchocyon were a consequence of the extreme enlargement of frontal bones. Instead, within the subfamily Macroscelidinae, the differences between genera were based on modification involving other bones, mainly mastoids and nasals, as shown by the deformation grids. A cluster analysis confirmed the traditional subdivision in two subfamilies (Rhynchocyoninae and Macroscelidinae) but suggested a different relationship among the recognized genera belonging to Macroscelidinae. Our results are congruent with data obtained from previous biochemical research and support the traditional subdivision in two subfamilies, the monophily of the genus Elephantulus and its closeness with Petrodromus, relating to their similar cranium shapes. The latter presumably is a case of gigantism as adaptation to forest habitats. Further studies on all the species of Elephantulus could provide new evidence for assessing the relationships within this clade, including Macroscelides that by the present analysis appeared as a well-distinguished taxonomic entity.