Evolution in Africa

Abstract

Africa and South America became completely separated during the Turonian (Upper Cretaceous, 90 m. y. B. P.). The first fossils of mammals appear in Africa only during the Eocene (Coonke, 1972: 96). From what is known, it appears that an African group of orders had been developing in that continent for a longer time than is suggested by the fossil record. These orders, Sirenia, Proboscidea, Hyracoidea, Tubulidentata and Embrithopoda, had so many primitive characters in common that they were united by Simpson (1945) in the Superorder Paenungulata. All other groups of Artiodactyla and Perissodactyla (see Fig. 85) are accepted as immigrants from Eurasia, having entered Africa at different times when land connections were established with various parts of Eurasia. Cooke (1972: 130) has summarized the palaeogeographic and palaeontological history of Africa as follows:

‘The African continent has long been regarded as a “refuge” for the survival of archaic forms of life, but in recent years evidence has been accumulating which serves to emphasize the essentially indigenous nature of the living and extinct mammalian faunas. (...) Through most of geological time Arabia has been basically part of the African continent, the Red Sea rift developed as a terrestrial trough in the Oligocene, was invaded from the Mediterranean in the Miocene, and connected through the Indian Ocean in the Pliocene. The pre-Mediterranean Tethys Sea cut Arabo-Africa off from Eurasia during much of the Mesozoic and Tertiary. Temporary land or island connections occurred during the Paleocene elevation of the Arabo-African block, during the late Oligocene orogenesis in the Atlas and the Alps, and again near the end of the Mio­cene. At those times there was opportunity for limited faunal interchange between Arabo-Africa and Eurasia. From a Paleocene ferungulate stock, already possessing early antracotheres and hyaenodonts, the proboscideans, hyracoids and sirenians developed as new elements in Africa. (…). In the late Oligocene there was an export of African stock to Eurasia in exchange for importation of some perissodactyls, fissiped carnivores, and perhaps basic suid, tragulid, and palaeomerycid-bovid elements. Lesser interchanges took place in the later Miocene, contributing African forms to Eurasia and admitting hipparionids to Africa. During the Pliocene great diversification took place among the African Proboscidea, Bovidae and Suidae in particular, but the Ethiopian region was effectively isolated from Eurasia until the end of the period. However, Arabia became firmly linked to Asia and probably furnished much African material to that continent.’