From shrews to blue whales, placental mammals are among the most diverse and successful vertebrates on the Earth. Arising sometime near the Late Cretaceous, this broad clade of mammals contains more than 1,000 genera and approximately 4,400 extant species. Although much studied, the origin and diversification of the placentals continue to be a source of debate.

Paleontologists Kenneth D. Rose and J. David Archibald have assembled the world's leading authorities to provide a comprehensive and up-to-date evolutionary history of placental mammals. Focusing on anatomical evidence, the...