Zoogeographie evidence for the origins of the Hominidae

Africa is usually taken to be the origin point of the human lineage, and so far as the later stages of the Pliocene and Pleistocene are concerned this is generally accepted as true beyond reasonable doubt. Nevertheless some doubts about this matter have been raised in recent years—in particular regarding the origins of Homo erectus (White 1995; Dennell 2004)—and it would always be unwise to assume that the fossil record will never surprise us. We return to this point later below. However, as we have seen, the Primates themselves did not originate in Africa, and while emphasizing their incursion during the Oligocene or perhaps even the Middle Eocene may seem like an academic nicety, it is worth stressing that the intermediate period of the mid- and later Miocene witnessed emigrations and perhaps also reimmigrations.

The apes of the subfamilies Dryopithecini and Kenyapithecini that dispersed from Africa underwent a considerable radiation in Eurasia until the end of the Mid-Miocene, around 7-9 Ma (Andrews and Bernor 1999), but in Africa apes are scarce between perhaps 15 Ma and a reappearance at Lothagam at the very end of the Miocene (Andrews and Humphrey 1999; Leakey and Harris 2003). Interpreting such absence in the fossil record is always hazardous, since it may indicate no more than an absence of suitable deposits or inadequate search and recovery. But if it is a real pattern then it is perhaps among those Eurasian advanced hominid apes that we should expect an ancestor for the later great ape and human lineage of the subfamily Homininae. The possibility that the European Dryopithecini make the most plausible candidates has been both proposed (Begun 1993) and questioned (Andrews 1992, 1996; Andrews and Bernor 1999) on several details of taxonomy and systematics, but Solounias et al. (1999) have raised the question again in the context of understanding wider issues of the relationship between faunas of southeastern Europe and Africa. The latter authors point out that many of the savanna-dwelling mammals of Africa may well have originated in what they term the Pikermi Biome, based on the rich Late Miocene Greek locality of Pikermi. They cite somewhat longer necked and thus more advanced giraffes, rhinos ofthe extant genera Diceros and Ceratotherium, the false sabretoothed cat Dinofelis and the larger bone-smashing hyenas Belbus beaumonti and Adcrocuta eximia as offering primary evidence for such an origin, and it is indeed clear that such animals do make their first appearance in Africa in the latter part of the Miocene. Overall, by around 8 Ma, over the middle part of the Miocene, there is an evidence of considerable incursion from Eurasia generally into Africa if we add to the above list the smaller to midsized and dog-like hyenas of the genera Protictither-ium, Ictitherium, Hyaenictitherium, Lycyaena, and Hyaenicits, the sabretoothed cat

Machairodus, a range of mustelids, and a number of antelopes (Vrba 1995; Werdelin and Turner 1996; Turner and Anton 2004). The impetus for this movement appears to have been a major shift in climate, changing the western European vegetation from subtropical evergreen forest to more deciduous and dry woodland and provoking a turnover in mammalian fauna that Agusti et al. (1999) termed the mid-Vallesian Crisis. By around 9 Ma, the dryopithecine hominids were extinct in Western Europe, although they managed to survive until perhaps 7.5 Ma in Italy and China (Andrews and Bernor 1999). A movement of early hominid apes back into Africa is therefore entirely plausible as part of this larger pattern of dispersion.

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