Among the notable trends seen in this year's highlights in mammalian aging research is an awakening of interest in the assessment of age-related measures of mouse health in addition to the traditional focus on longevity. The analysis of molecular phylogenetic data has advanced the knowledge of the relationships among the major groups of living vertebrates. The analysis of molecular phylogenetic data has advanced the knowledge of the relationships among the major groups of living vertebrates. Whereas the molecular hypotheses generally agree with traditional morphology-based systematics, they sometimes contradict them. This book reviews the major controversies in vertebrate phylogenetics and the contribution of molecular phylogenetic data to their resolution: (a) the mono- paraphyly of cyclostomes, (b) the relationships among the major groups of ray- finned fish, (c) the identity of the living sistergroup of tetrapods, (d) the relationships among the living orders of amphibians, (e) the phylogeny of amniotes with particular emphasis on the position of turtles as diapsids, (f) ordinal relationships among birds, and (g) the radiation of mammals with specific attention to the phylogenetic relationships among the monotremes, marsupial, and placental mammalas.