Griphopithecidae

Bonis & Koufos, 1999

Oreopithecus

Western Europe

8.5-8.0 Ma

Harrison & Rook, 1989

Lufengpithecus

Asia

8.0-7.0 Ma

Ciochon & Etler, 1994

the other Eurasian hominid Griphopithecus (also with thick molar enamel), which first appears in Turkey around this time (Heizmann & Begun, 2001; Andrews et al., 1996). Dryopithecus, however, does not appear in the fossil record of Europe until around 12.5 Ma (Andrews et al., 1996; Andrews & Bernor, 1999; Begun, 2001). Begun (2001) suggests that either Kenyapithecus from Fort Ternan (Kenya) or Griphopithecus from Turkey represent the likely ancestral ape that gave rise to Dryopithecus, and he concludes that the African hominid clade evolved in Europe from a Dryopithecus-like ancestor. He argues that in terms of its morphological condition, Kenyapithecus cannot be linked to the extant African hominid clade (to the exclusion of Dryopithecus) because it shares only primitive features with them (see also Begun, 1992b). He believes that the immediate ancestor to the African hominids, while far from resolved, is likely to be Dryopithecus or a Graecopithecus-like hominid; either way the ancestral 'African" hominid is said to be from Eurasia, migrating back into Africa around 9 Ma (see Table 2.1).

Any paleobiogeographical interpretation of hominid origins is bound to be accused of speculation. The usual comment is that preservation bias will give a slanted view and overemphasize the importance of species known as opposed to the great majority of species that we will never know about. This, however, is true for any paleontological interpretation and is not a strong argument for dismissing the available evidence. If this were the case, then we should not attempt to reconstruct phylogenies based on the paleontological record, because they obviously fall "victim" to the same "logic." While certainly not dismissing the potential affects of preservation bias, absence of evidence is not evidence of absence; any hypothesis has to be based on the evidence currently available (Begun, 2001). While there are significant differences in the details of the schemes just reviewed, the overall conclusion is that Eurasia has played a major role in the paleobiogeographical origins/dispersals of the hominids.

The available evidence suggests that Africa during the middle and later Miocene was impoverished in terms of hominid species, compared to the explosion seen in Eurasia (e.g., see Table 2.1). This cannot be convincingly argued to be the result of a lack of geological exposures from this time period (see discussion in Begun, 2001), which further suggests that the origin of the extant hominids is from Eurasia and not from an endemic African ape population. As already discussed, most experts accept that the nonhominid fossil samples (which also suffer from preservation bias) are strong evidence for an influx of nonendemic fauna into Africa during the later Miocene (Barry et al., 1985; Thomas, 1985; Tong & Jaeger, 1993; Bernor et al., 1996; Gentry & Heizmann, 1996; Solounias et al., 1999; Begun, 2001). Given that the available hominid fossil evidence also points to this conclusion, the most parsimonious scheme is to accept that the basal hominid also originated from outside of Africa.

The differential distribution of the hominids can be explained by a change in worldwide climatic conditions during the middle Miocene. Around 15 Ma there was increasing expansion of continental ice in high latitudes, resulting in the establishment of a large ice cap in the region of Antarctica. Significant cooling in the northern high latitudes is indicated by seasonal ice rafting of debris into the North Atlantic. This cooling affected Africa, because it became drier and cooler. Climate change in Africa was further emphasized by the major continental uplift that affected both eastern and southern Africa. This rise of interior plateaus, especially the Ethiopian Plateau, blocked moisture from the Atlantic Ocean in the west, leading to a rain-shadow effect over much of eastern Africa, with increased seasonality in precipitation accentuated (Owen-Smith, 1999; see also Kingston, 1999). Finally, with the main uplift phase of the Himalayas and the Tibetan Plateau by the late Miocene, monsoonal climates brought on further climatic and paleoenvironmental changes (Cerling et al., 1997; 1998; R.C.I. Wilson et al., 2000).

The previously held "consensus" view that the late Miocene and early Pliocene epochs of northern and eastern Africa were marked by a rapid "drying out" and that the endemic fauna were characterized by an adaptive shift to cope with the changed circumstance (Andrews & Van Couvering, 1975; Coppens, 1994, 1999) may be an over simplification of events. As argued by Solounias et al. (1999), there is evidence that much of the extant African savanna fauna do not have origins in Africa but, rather, migrated into Africa from more northerly latitudes, including Greece and Iran. These migrant fauna will have replaced much of the African endemic fauna because these new immigrant species were already adapted to the new conditions prevailing in Africa as a result of global cooling. As such, what was previously designated as "African fauna" associated with Graecopithecus (de Bonis & Koufos, 1994, 1999, 2001; de Bonis et al., 1992) may actually have been endemic to Eurasia.

During the Early Miocene, much of Eurasia was covered in evergreen woodlands associated with increasing seasonality and aridity. During the early/middle Miocene, African mammal species, including primates, expanded their range from the African tropical forests and woodlands to the Eurasian woodlands, which were probably much more open in structure (Andrews & Bernor, 1999). Finally, in Eurasia, the African elements further adapted to the Eurasian conditions, and eventually their adaptations became exaptations for the changing conditions in Africa, which may have enabled them to occupy successfully and outcompete much of the endemic fauna. Indeed, the hominoid fossil record supports this interpretation because the Eurasian hominids (e.g., Graecopithecus) bear a closer relationship to the extant Gorilla and Pan than do any of the documented "endemic" Miocene hominoids (Andrews, 1992; D. Dean & Delson, 1992; Cameron, 1997a; partly Begun, 1994b; Singleton, 2000; S. Ward & Duren, 2002; Cameron, in press a).

It is probable, given the available evidence, that the later hominids of Eurasia originated from the thick-enameled Griphopithecus sometime during the middle Miocene, between 16 and 14 Ma. Griphopithecus is commonly associated with forests in drier and more strongly seasonal conditions, with summer rainfall and prolonged dry seasons (Andrews & Humphrey, 1999). This may have led to the evolution in western Europe of the thin-enameled Dryopithecus, which is associated with tropical to subtropical conditions, while in Eurasia this resulted in the appearance of the hyperthick molar enameled Graecopithecus, which occupied conditions not too dissimilar to its presumed Griphopithecus-like ancestor. Thus, the Eurasian hominids retained the primitive condition of thick molar enamel, while Dryopithecus, which was occupying a new environmental niche (requiring a more frugivorous diet), evolved thinner molar enamel (to help further define its postcanine occlusal cristae) as well as suspensory locomotion to help move through the closed forest habitat (see Andrews & Humphrey, 1999; Agusti et al., 2001).

The primitive hominid nature of Dryopithecus, compared to the derived status of Graecopithecus, may be a partial result of its inferred isolation from the southeastern Mediterranean hominids, caused by the separation of the Greek and Albanian landmass from central Europe by the Aegean connection with the Paratethys (see R.M. Jones, 1999; Rogl, 1999). Dryopithecus species and fossil small-bodied apes (e.g., Anapithecus, Pliopithecus) of western Europe appear to have adapted successfully to the more wet subtropical forests of northern Europe, as evidenced by their dental morphology and suspensory locomotion (Andrews & Bernor, 1999). With the encroaching cooler and drier conditions, however, they appear to have failed to adapt to the more open habitat, thus "slowly" being driven to extinction. For example, during the Middle Miocene, deciduous plant communities invaded Europe gradually, replacing the tropical plant communities (Andrews & Bernor, 1999). This climate change is further indicated by the retreat of the z-coral communities (which today thrive in the Caribbean and Indopacific) from the then-flooded Vienna Basin, southward to the northern coast of the Mediterranean during the Late Miocene (Rosen, 1999; Andrews & Bernor, 1999). The demise of Dryopithecus and the small-bodied apes of Europe can be equated with processes resulting in numerous "natural" extinctions observed today. These include: changed paleohabitat; resource competition by other nonprimate species as they occupied the new, changing environmental conditions; increased predation by new, large-bodied carnivores; and/or subsequent genetic isolation, finally pushing them into extinction.

Graecopithecus is likely to have been less affected by climate and paleohabitat change, because of its preexisting conditions and its ability to move between Eurasia and Africa. Indeed, its hyperthick molar enamel and inferred terrestrial locomotion suggest that it was well adapted to the drier conditions of the eastern Mediterranean, with a broad dietary regime (Andrews & Bernor, 1999). Indeed, Dryopithecus from western Europe disappears from the fossil record 1 million years earlier than the southern hominids; although its relative Oreopithecus persists for an additional 2 million years. While Graecopithecus disappeared from the Eurasian fossil record by 10 Ma, it is possible that southern populations of it (or other closely related taxa) may have further increased their range to include northern Africa, by fragmentation or splitting of territorial ranges, e.g., vicariance (see Andrews & Bernor, 1999; Strait & Wood, 1999). It is also possible that surviving populations of these hominids in Eurasia migrated (along with other fauna) back into Africa in order to take advantage of the changing conditions within this continent while the remaining hominid populations in Eurasia eventually succumbed to competition from other, nonprimate species and/or ever-increasing climate and habitat change.

It is only after the original "Out of Africa" by early-middle Miocene African hominoid taxa into Eurasia around 16 million years ago that we see the explosion in hominid species and genera, so the modern African hominid lineage is likely to have its origins in Eurasia (Figure 2.12). This ancestor gave rise to the last common ancestor of the extant African and Asian hominid lineages. By 15 million years ago the basal hominid was present in Eurasia, the best candidates being either Griphopithecus or a proto-Dryopithecus population. From this ancestor, the extant apes ultimately emerged. The Asian hominid lineage was first established with

Griphopithecus

Figure 2.12 ► Miocene hominid dispersals out of and into Africa. (1) Kenyapithecinae (Griphopithecus) dispersal into Eurasia around 17 million years ago, while Kenyapithecus is endemic to Africa. (2) Evolution of the Dryopithecinae (Dryopithecus and Oreopithecus) in Europe between 12 and 8 million years ago. (3) Dispersal into Asia around 13 million years ago from Eurasia of the Miocene Ponginae (Ankarapithecus, Sivapithecus, and Lufengpithecus). (4) During the Late Miocene Graecopithecus disperses back into Africa, following other large and small mammal dispersals from Eurasia into the African continent due to environmental change, replacing many previous Miocene endemic fauna.

Figure 2.12 ► Miocene hominid dispersals out of and into Africa. (1) Kenyapithecinae (Griphopithecus) dispersal into Eurasia around 17 million years ago, while Kenyapithecus is endemic to Africa. (2) Evolution of the Dryopithecinae (Dryopithecus and Oreopithecus) in Europe between 12 and 8 million years ago. (3) Dispersal into Asia around 13 million years ago from Eurasia of the Miocene Ponginae (Ankarapithecus, Sivapithecus, and Lufengpithecus). (4) During the Late Miocene Graecopithecus disperses back into Africa, following other large and small mammal dispersals from Eurasia into the African continent due to environmental change, replacing many previous Miocene endemic fauna.

species occupying present-day Turkey (Ankarapithecus), Pakistan and India (Sivapithecus), and China (Lufengpithecus), while slightly later the African lineage was established in Eurasia with the appearance of Graecopithecus. With the changing climatic conditions of the later Miocene, Graecopithecus or a closely related species may have increased its range from present-day Greece-Albania into Eurasia proper as well as into Africa. This migration was likely part of a general faunal migration into Africa from the surrounding regions. If this scenario is correct, then the early African hominids, which gave rise to the extant African hominids, were not endemic to Africa.

Until very recently, the available evidence suggested that Africa during the middle and later Miocene was impoverished in terms of hominid species, compared to the explosion seen in Eurasia. Most experts now accept that the nonhominid fossil record provides strong evidence for an influx of nonendemic fauna into Africa, during the later Miocene; the recent discoveries of Orrorin and Sahelanthropus and the earlier discovery of the specimen from Lothagam (all discussed in the next chapter) suggest that the Late Miocene of Africa was not as impoverished as we once may have thought (see also S. Ward & Duren, 2002). There is little evidence to support a close phylogenetic connection between the extant African hominids and the dryopithecines from Europe, though such a relationship with the Eurasian hominid Graecopithecus cannot be ruled out (see Andrews, 1992; D. Dean & Delson, 1992; Cameron, 1997a, in press a). While the explosion of the Eurasian hominids during the middle and later Miocene resulted, in most cases, simply in extinction, some unknown hominid genera, possibly descendants of a Kenyapithecus--like or Graecopithecus-like hominid, survived to give rise to the proto-gorilla and proto-chimpanzee and, of course, ultimately proto-humans.

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