Reflections on higher mammalian phylogenetics

Abstract

For well over a decade, the higher-level relationships of mammals has been the focus of intensive and broad-ranging investigations. The sources of evidence drawn upon for this purpose are both traditional (e.g., paleontology, skeletal morphology) and newly sampled (e.g., comparative gene sequencing). A basic methodology, nonetheless, pervades this diversity of sampling. Issues that concern all types of data include the assumptions for recognizing homology, the techniques for building trees, the justification of parsimony and weighting, and the means of evaluating and comparing different results. In some areas (e.g., paleontology, molecular comparisons), we have been continual or even explosive expansion of the data base. In other areas (e.g., comparative behavior, physiology, or comparisons involving many aspects of nonskeletal morphology), the expansion has been far less dramatic. Codifying large arrays of characters is no substitute for penetrating studies of comparative form, function, and ontogeny or careful sampling of a diversity of genes. It is hoped that the latter emphases are maintained and nourished. The results of all this recent activity show a mixed profile of resolution for higher-level patterns of phylogeny. Particularly, the higher eutherian mammal radiation still presents many problems. Such challenges, however, have attracted an unprecedented level of synthesis and interaction.