About 320 million years ago a group of reptiles known as the synapsids emerged and forever changed Earth's ecological landscapes. This book discusses the origin and radiation of the synapsids from their sail-backed pelycosaur ancestor to their diverse descendants, the therapsids or mammal-like reptiles, that eventually gave rise to mammals. It further showcases the remarkable evolutionary history of the synapsids in the Karoo Basin of South Africa and the environments that existed at the time. By highlighting studies of synapsid bone microstructure, it offers a unique perspective of how suc