High Quality Content by WIKIPEDIA articles! The list of extinct cetaceans features the extinct genera and species of the order Cetacea. The cetaceans (whales, dolphins and porpoises) are descendants of land-living mammals, the even-toed ungulates. The earliest cetaceans were still hoofed-mammals. These early cetaceans became gradually better adapted for swimming than for walking on land, finally evolving into fully marine cetaceans.