Dr. Zack studies the evolution of mammals, focusing on the early Cenozoic radiation of placental mammals, particularly the phylogeny and evolution of Paleocene and Eocene carnivorous placental mammals and their relationships to extant placental carnivores. Dr. Zack also has a special interest in the postcranial morphology, particularly ankle morphology, of early Cenozoic placentals and its implications for the autoecology and phylogeny.