Phylogenetic Relationships Among Treeshrews (Scandentia): A Review and Critique of the Morphological Evidence

Although the supraordinal relationships of Scandentia (treeshrews) have been studied in great detail from both morphological and molecular perspectives, the phylogenetic relationships among treeshrews have been largely ignored. Here we review several published studies of qualitative morphological variation among living treeshrews and their contribution to our understanding of intraordinal phylogenetic relationships. Reanalysis of the data from each of these studies demonstrates that none of the trees in the original publications represents the most parsimonious interpretation. In addition to performing new analyses, we argue that all such studies to date suffer from one or more fundamental shortcomings, notably the failure to include reference to nonscandentian outgroups and the a priori assumption of generic monophyly of the relatively speciose genus Tupaia. Parsimony analyses of these data sets fail to resolve either intergeneric or interspecific relationships. Finally, several inconsistencies and conflicts with respect to character coding both within and between published studies are discussed. We conclude that a more rigorous investigation of morphological character state variation is sorely needed, one that explicitly identifies voucher specimens and does not make any assumptions of generic monophyly. This is necessary not only for the purpose of resolving phylogenetic relationships, but also for inference of ancestral states in a group that continues to figure prominently in studies of placental mammal diversification.