Afrotheria is a clade of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews (also known as sengis), tenrecs, aardvarks, hyraxes, elephants, sea cows, and several extinct clades. They share few anatomical features but many are partly or entirely African in their distribution. This probably reflects the fact that Africa was an island continent through the early Cenozoic. Because the continent was isolated by water, Laurasian groups such as insectivores, rabbits, carnivorans and ungulates could not become established. Instead, the niches occupied by those groups were filled by tenrecs, hyraxes and elephants that evolved from the ancestral afrothere. This adaptive radiation may have occurred in response to the Cretaceous–Paleogene mass extinction.