Traditionally, the golden moles of southern Africa and the tenrecs of Madagascar and Africa were grouped with the hedgehogs, shrews and a number of other small, relatively primitive mammals in Insectivora, less because of any overwhelming morphological evidence than simply because they were difficult to place in any other order. Toward the end of the 20th century, however, a wealth of new information started to become available as a result of advances in the study of genetics. One of the most significant advances was the recognition that about one third of all living placental mammal orders appear to share a common descent. This apparently diverse group, known as Afrotheria, includes the tenrecs and golden moles, the elephant shrews, Aardvark, hyraxes, elephants and sirenians. It is thought that the Afrotheria has an ultimately Gondwanian origin sometime in the Cretaceous and that its members evolved and radiated in Africa during the time when Africa was drifting and isolated from the other continents.