The 26 orders of living mammals occur in a variety of habitats; 97.5% of the species occupy terrestrial while only 2.5% inhabit marine environments. The most recent complete compilation lists 136 families, 1,135 genera, and 4,629 living and recently extinct species. The Ethiopian region possesses the most diverse fauna (52 families, 17 endemic) and 23% of all described species. This region has the highest generic and species endemism; almost 80% of the genera and >90% of the species are endemic. Fauna of the Oriental region also is rich (50 families, three endemic), including >20% of the world's species. The Palearctic region possesses 42 families (none endemic) and 18% of the world's species. The Australian region includes 10% of the world's species in 28 families (12 endemic); >60% of the genera and almost 90% of the species are endemic. The richest diversity of mammals in the New World occurs in the Neotropical region with 50 families (19 endemic) and 24% of the world's species (>80% endemic). The Nearctic region (37 families, two endemic) is home to 14% of all described species. Three terrestrial orders (Primates, Perissodactyla, and Proboscidea) and two marine orders (Cetacea and Sirenia) require immediate conservation efforts. Within the remaining 21 orders, ca. 30% of Old World and 15% of New World families are at risk. Additionally, almost 15% of the world's species are rated as endangered or vulnerable, and another ca. 10% are categorized as potentially vulnerable; these species warrant conservation strategies. The areas of the world with the greatest mammalian diversity are also the most poorly known, so conservation needs may be under-represented in those regions.
