- ORIGINAL SCIENTIFIC ARTICLE
- Open Access
Apes and Tricksters: The Evolution and Diversification of Humans’ Closest Relatives
© Springer Science+Business Media, LLC 2010
- Published: 3 August 2010
The evolutionary history of humans comprises an important but small branch on the larger tree of ape evolution. Today’s hominoids—gibbons, orangutans, gorillas, chimpanzees, and humans—are a meager representation of the ape diversity that characterized the Old World from 23–5 million years ago. In this paper, I briefly review this evolutionary history focusing on features important for understanding modern ape and human origins. As the full complexity of ape evolution is beyond this review, I characterize major geographic, temporal, and phylogenetic groups using a few flagship taxa. Improving our knowledge of hominoid evolution both complicates and clarifies studies of human origins. On one hand, features thought to be unique to the human lineage find parallels in some fossil ape species, reducing their usefulness for identifying fossil humans. On the other hand, the Miocene record of fossil apes provides an important source for generating hypotheses about the ancestral human condition; this is particularly true given the dearth of fossils representing our closest living relatives: chimpanzees and gorillas.
- Hominoid evolution
- Human origins
From this perspective, the origin of the human lineage can only be properly understood within the context of the larger tree of hominoid diversity from which our small but vigorous branch emerged. Today, there are only five types of hominoid left on this tree, and with the exception of gibbons, none of these is very speciose. This heavily pruned bole represented in Fig. 1 stands in dramatic contrast to the vibrant, multifurcating tree of fossil apes that lived in the Miocene epoch, 23.0–5.3 million years ago (Ma). Even conservative practitioners (“lumpers,” in common parlance) might name dozens of ape genera from the fossils that have been discovered thus far; “splitters” might recognize more than 50. Considering the potential for multiple species within each of these groups, it seems that one could hardly take a step through the Miocene geography without tripping over another type of ape.
Convenient phylogeographic groups of hominoids
First modern apes
Ancestral African apes
In this paper, I review briefly the origin and evolution of hominoids, focusing primarily on the rich fossil record from the Miocene epoch. Since a detailed discussion of every Miocene ape is beyond the scope of this review, I have instead adopted a phylogeographic approach that samples better-known and key fossil groups from the geographic distribution of hominoid lineages.
The oldest ape-like fossils are found in Africa from a time when it was still an island continent. As early as 25 million years ago (Boschetto et al. 1992), ape-like primates were living in East Africa, and this diverse and successful community thrived for more than ten million years (Kunimatsu et al. 2007; Pickford and Kunimatsu 2005). Many researchers regard at least some of these primates as true hominoids—belonging to the ape and human lineage—while relegating others to more primitive groups. But regardless of whether some are classified as “stem catarrhines” (related to but not specifically belonging with either Old World monkeys or apes) and others may be “stem hominoids” (related to but not uniquely linked to modern ape lineages), the importance of these primates for understanding the origin of the ape–human lineage (Andrews and Harrison 2005) makes it appropriate to discuss them simply as STEMs: stem taxa from the Early Miocene.
Despite its many primitive skeletal features, Proconsul does display some features that may warrant its inclusion among apes. The most obvious ape-like feature of Proconsul is the lack of an external tail (Nakatsukasaa et al. 2004; Ward et al. 1991). It also shares enhanced grasping capabilities (Begun 1994) and a stabilized elbow joint (Rose 1988, 1992) with all of the extant apes, and has a few facial features reminiscent of the living great apes (Rae 1997, 1999, 2004). Interestingly, the largest but also oldest species of Proconsul (Proconsul major, also called “Ugandapithecus” by some workers) is more similar to modern apes than the smaller, younger species (Harrison 2002). Additional evidence suggests that Proconsul’s growth and development was slower than that of Old and New World monkeys, more like the life history of the apes (Kelley 1997). In all, the number of features shared by Proconsul and the surviving modern apes are relatively few, but even a small number of shared derived features is regarded as significant evidence compared to an otherwise very primitive skeleton (see Harrison 2002 for a different interpretation). For this reason, most researchers place this STEM taxon among the earliest fossil apes.
While not as well known as Proconsul, other STEMs display intriguing similarities to the modern apes. Morotopithecus is one of the oldest members of this group, living in Uganda more than 20 Ma and combining a primitive face with more modern back and shoulder, indicative of suspensory behaviors (MacLatchy 2004). In a contrasting example, the smaller primate Rangwapithecus is nearly as old (Pickford and Andrews 1981) and has a modern ape-like lower face (McNulty 2003; see also Ward et al. 1983; McCrossin and Benefit 1994) but a primitive Proconsul-like skeleton (Rose 1997; Ward 1997a). This sort of evolutionary mosaicism—where more advanced features first appear in multiple species rather than aggregating in a single lineage over time—is becoming commonplace as we learn more about primate evolution, and serves to caution researchers against creating simple, linear models of adaptation and evolution.
By the late Early Miocene, Africa was no longer isolated from the rest of the Old World, and terrestrial connections to Eurasia provided long periods of faunal interchange between the land masses (Rögl 1998). Apes first appeared in Eurasia around this time at fossil sites in Germany and Turkey just younger than 17 Ma (Heizmann and Begun 2001). By 15 Ma, a more advanced grade of ape also inhabited East African sites, overlapping with a few long-surviving lineages of STEM primates. The exact relationships between earlier East African STEMs and these more advanced apes are still debated, but most researchers agree that the new Middle Miocene species belong in the ape and human lineage (Begun 2007; Begun et al. 1997; Benefit and McCrossin 1995; Harrison 1992, 2010; Ward and Duren 2002).
Paleoanthropologists have long been criticized for liberally assigning new names to every new fossil discovery. This is demonstrably not the case with the Middle Miocene apes from Kenya, which researchers lumped into the genus Kenyapithecus for more than three decades. Following the discovery of this advanced grade of ape at the 14-million-year-old site of Fort Ternan, Kenya (Leakey 1962), Louis Leakey’s Kenyapithecus became a catchall for large-bodied Middle Miocene apes found throughout that country. This was quite reasonable considering the scarcity and fragmentary nature of most specimens, but the eventual discovery of two partial skeletons from sites at Nachola and Kipsaramon caused most workers to identify three distinct genera: Kenyapithecus from Fort Ternan, Nacholapithecus from Nachola (Ishida et al. 1999), and Equatorius from Kipsaramon and Maboko (Ward et al. 1999; Harrison 1992; but see Kelley et al. 2000; Benefit and McCrossin 2000).
By the late Middle Miocene, the African record of fossil apes becomes very sparse; a few fragmentary specimens span the intervening time prior to the appearance of the earliest fossil humans around seven million years ago. These few, however, seem to represent late-surviving members of the STEM primates (Begun 2007; Hill et al. 2002; Kunimatsu et al. 2007; Olejniczak et al. 2009) and perhaps early examples of the lineage of African apes and humans (see below). Meanwhile, it is Europe and Asia that record the subsequent chapters of ape evolution through the Middle and Late Miocene. In fact, the terrestrial connection between Africa and Eurasia that began in the Early Miocene is paralleled in a taxonomic connection between fossil sites in Kenya and Turkey, with a newly named species of Kenyapithecus (Kenyapithecus kizili) from the Turkish site of Paşalar (Kelley et al. 2008).
After apes first appear in Eurasia ∼16.5 Ma, the record of their tenure there disappears until about 13 Ma. Subsequent to that, a diversity of fossil apes evolves over the next seven million years, spanning the broadest reaches of the Eurasian landmass. While some researchers have integrated both European and Asian fossil apes into a broad clade leading ultimately to the orangutans (e.g., Moyà Solà and Köhler 1993; Köhler et al. 2001), the geographic organization adopted here (see Begun 2005) reflects the more widely held opinion that the Asian fossils are specifically related to the orangutan (but see Pilbeam 1997), while European fossil apes are more broadly ancestral to all great apes (Andrews 1992; Andrews and Martin 1991; Harrison 2010; Harrison and Rook 1997), with perhaps one or two grouped more closely with African apes (Begun 2002, 2009; Begun and Kordos 1997; Rose 1997).
One of the most fascinating European apes is named Oreopithecus and was found in seven-million-year-old deposits in Italy and Sardinia. Like Sardinia today, much of Italy was an island during that time, and in that isolation, Oreopithecus evolved some interesting characteristics. In the history of paleoanthropology, this ape has occupied a wide variety of phylogenetic positions, including being associated with Old World monkeys (Szalay and Delson 1979) or the primitive African STEM Nyanzapithecus (Harrison 1986; von Koenigswald 1969). Today it is recognized as a true ape (e.g., Harrison and Rook 1997) and is particularly relevant here because of its unique skeletal features. Several authors (Köhler and Moyà Solà 1997; Rook et al. 1999) have interpreted the foot and pelvis of Oreopithecus as indicative of bipedal postures, arguing that relaxed predation pressures on an island might have promoted increased terrestriality. In particular, they argue that the foot of Oreopithecus was built to support an upright stance during prolonged bipedal feeding and perhaps bipedal shuffling between food resources (Köhler and Moyà Solà 1997). Both pedal and pelvic evidence for bipedalism have been criticized, and there is strong evidence for suspensory adaptations in this ape (Begun 2007; Wunderlich et al. 1999). Nevertheless, the scenario suggested for the bipedal evolution of Oreoptihecus is similar to some (e.g., Jolly 1970) proposed for the origins of human bipedal postures.
The modern geographic distinction between Europe and Asia might very well have delineated major lineages of apes in the Miocene (Begun 2005; but see, e.g., Köhler et al. 2001). Excepting the scanty “dryopith”-like remains in Georgia and China, this phylogeographic separation makes intuitive sense given the narrow terrestrial connections between the two continents that lie within latitudes inhabitable by apes. Indeed, these zones of faunal interchange would have been complicated and disrupted during the Miocene by shifting arrangements of landmasses and pre-Mediterranean water bodies as Eurasia gradually accommodated the tectonic apposition of the African continent (see, e.g., Rögl 1998; Harzhauser and Piller 2007).
It is impossible to describe ape evolution in Asia without mentioning the aptly named Gigantopithecus. Known from one species in the Miocene Siwalik sites of India and Pakistan and a second species that survived to less than one million years ago in Southeast Asia (Rink et al. 2008), this taxon far surpassed the body size of even the largest male gorillas (Johnson 1979). Though only known from isolated mandibles and teeth, this curious ape is relevant here because of an interesting similarity shared with the human lineage: dramatically reduced canines in males and females and the corresponding loss of the canine–premolar honing complex (e.g., Pilbeam 1970; Frayer 1973; Wang 2009). In species that have large canines, which include most fossil and living apes, this complex provides for the upper canines to be continually sharpened by wearing (“honing”) against the tooth immediately behind the lower canine: the P3. Apes that have reduced their canine size, like humans, may lose the canine–premolar honing complex. Thus, based partly on the reduced size and dimorphism of its canines, some early researchers suggested that Gigantopithecus might be intermediate between apes and humans (Weidenreich 1946) or even directly ancestral to the human lineage (Eckhardt 1972, 1973, 1975; Frayer 1973; Robinson and Steudel 1973). However, it is now widely accepted that this terminal gargantuan lineage represents a branch in the evolutionary history of pongines.
With the exception of the human lineage, there are almost no fossils that can be linked to modern African apes. Recent discovery of isolated chimpanzee teeth, dating to around 500,000 years ago (McBrearty and Jablonski 2005), are the first good examples linked to an African ape genus. Beyond these few specimens, the evolutionary history of Gorilla and Pan is completely unknown. The preponderance of Eurasian apes during the Late Miocene has prompted many workers (e.g., Begun et al. 1997; Begun 2005; Stewart and Disotell 1998) to suggest that the African ape lineage arose in the northern continents, likely in Europe, before migrating into Africa. Begun (e.g., Begun 1994, 2002, 2005, 2007, 2009; Begun et al. 1997; Begun and Kordos 1997) includes Dryopithecus among these ancestral hominines (the lineage of African apes and humans), but the Greek taxon Ouranopithecus is seen by many researchers as the best candidate for this role (Benefit and McCrossin 1995; Andrews 1992; Andrews 1990; Dean and Delson 1992; Andrews et al. 1996; McNulty 2005; but see Köhler et al. 2001).
One difficulty in assessing the validity of a European origin of African ape lineage is that the fossil record in the Late Miocene of Africa is so poor. For many years, a single fragmentary maxillary fossil named Samburupithecus was the best evidence of Late Miocene fossil apes in East Africa (Hill and Ward 1988; Ishida and Pickford 1997), though it is now recognized as a more primitive ape—perhaps even a late-surviving STEM lineage (Begun 2002, 2007)—and probably unrelated to the African apes. In 2007, however, two new fossil apes were announced from Late Miocene sites in Ethiopia and Kenya. Nakalipithecus from Kenya is nearly ten million years old and thought by its discoverers to represent the ancestral features of the African apes (Kunimatsu et al. 2007). Chororapithecus from Ethiopia is slightly older (10.5–10.0 million years ago) and has a size and morphology suggestive of modern gorillas (Suwa et al. 2007). Both of these recent finds are currently known from only a few specimens, and consensus on their evolutionary relationships awaits a broader review of the evidence by the scientific community. Nevertheless, a more complete Late Miocene record from Africa will provide a better test of the relationships between the living African apes and European fossil taxa. Ultimately, until we have a thorough understanding of the evolutionary history of gorillas, chimpanzees, and their hominine ancestors, we cannot do more than speculate about the features that characterized the human–chimpanzee common ancestor and therefore the origin of the human lineage.
Given this complex and tangled prehistory of apes (and tricksters), what can be said about the context of human origins? Many of the traits that we associate with humans—large brains, complex tool use, language, consciousness—almost certainly occurred long after our lineage parted ways with the ancestors of chimpanzees. If we retrace our steps on the hominin branch back toward their origin, two key features seem important: reduced canines (with the corresponding loss of the canine–premolar honing complex) and bipedalism. It is these traits that seem to distinguish even the oldest hominins from their simian cousins, and evidence of these features is repeatedly cited to demonstrate the “human-ness” of new fossil discoveries (Brunet et al. 2002; Leakey et al. 1995; Senut et al. 2001; White et al. 1994, 2009).
As has been shown here, however, reduction in canine size and the loss of the honing complex has happened several times in the fossil record of apes. Ouranopithecus, Gigantopithecus, and Oreopithecus all display some degree of canine reduction. This can also be seen in the modern pygmy chimpanzee, Pan paniscus (Kelley 2001). Complicating the matter is that most species of female apes have canines that are much smaller than their male counterparts (curiously, the monomorphic gibbons have “masculinized” canines in both males and females). Thus, identifying a fossil human from canine size requires that one clearly distinguish between male and female specimens on some criterion other than canine size and that one rule out alternative, convergent canine reductions such as those seen in recent fossil apes. Extracting that amount of information from the miserly fossil record can be difficult.
Bipedalism, then, and the many features that correspond to it, seems the best diagnostic measure of fossil humans. The bipedal postures of Oreopithecus are the best example of this behavior occurring convergently among apes (Köhler and Moyà Solà 1997; Rook et al. 1999), but this evidence is debatable (Begun 2007; Wunderlich et al. 1999). Bipedal postures also occur in the living great apes as they climb and clamber through the trees and in gibbons, which walk bipedally when they descend to the ground (e.g., Weidenreich 1946). These behaviors, even if they are relevant to the origin of bipedalism (Harcourt-Smith and Aiello 2004; Thorpe et al. 2007), do not permeate the skeleton in any significant way, however, and therefore do not confuse the identification of obligate bipeds in the fossil record. On the other hand, if occasional bipedalism in an arboreal context was generative in human prehistory (see, e.g., Begun 2005), then the diagnostic utility of bipedal skeletal morphology may diminish as one gets closer to the origin of our lineage. Add to this the complications of identifying bipedalism from cranial features (Biegert 1963) and the likely mosaic nature of bipedal evolution among contemporary fossil human species (Harcourt-Smith and Aiello 2004), and the debates that surround human origins seem not only reasonable but quite expected.
Identifying the earliest humans means, by necessity, that we can differentiate them from ancestral chimpanzees and gorillas. With little or nothing known about the ancestral forms of our closest relatives, we can at best impute their features using the modern species: a top-down approach. This is wrong on logical grounds—gorillas and chimpanzees have evolved over as long a time period as humans have—but is intuitively attractive because it seems obvious that the magnitude of human evolutionary change over this time has been substantially greater. The implications of this fact are easily misunderstood: while chimpanzees may be more similar to our last common ancestor than are modern humans, they still may not be very similar. Using chimpanzees as a model for the ancestral human may be greatly misleading (Senut 2007; White et al. 2009), and this is precisely why a detailed knowledge of ape evolution is so important to human origins research (Andrews and Harrison 2005). In the absence of a robust fossil record of gorillas and chimpanzees, it is only through a complimentary bottom-up approach—using the morphological diversity generated through 20 million years of ape evolution—that we can build reasonable hypotheses about the ancestral form which gave rise to the first fossil humans.
- Andrews P. Lining up the ancestors. Nature. 1990;345:664–5.Google Scholar
- Andrews P. Evolution and environment in the hominoidea. Nature. 1992;360:641–6.Google Scholar
- Andrews P, Harrison T. The last common ancestor of apes and humans. In: Lieberman DE, Smith RJ, Kelley J, editors. Interpreting the past: essays on human, primate, and mammal evolution in honor of David Pilbeam. Boston: Brill Academic; 2005. p. 103–21.Google Scholar
- Andrews P, Martin LB. Cladistic relationships of extant and fossil hominoids. J Hum Evol. 1987;16:101–18.Google Scholar
- Andrews P, Martin L. Hominoid dietary evolution. Phil Trans R Soc Lond B. 1991;334:199–209.Google Scholar
- Andrews P, Harrison T, Delson E, Bernor RL, Martin L. Distribution and biochronology of European and Southwest Asian Miocene catarrhines. In: Bernor RL, Fahlbusch V, Mittmann H-W, editors. The evolution of Western Eurasian Neogene mammal faunas. New York: Columbia University Press; 1996. p. 168–295.Google Scholar
- Begun DR. Relations among the great apes and humans: new interpretations based on the fossil great ape Dryopithecus. Yrbk Phys Anthropol. 1994;37:11–63.Google Scholar
- Begun DR. European hominoids. In: Hartwig W, editor. The primate fossil record. Cambridge: Cambridge University Press; 2002. p. 339–68.Google Scholar
- Begun DR. Sivapithecus is East and Dryopithecus is West, and never the twain shall meet. Anthropol Sci. 2005;113:53–64.Google Scholar
- Begun DR. Fossil record of Miocene hominoids. In: Henke W, Rothe H, Tattersall I, editors. Handbook of palaeoanthropology, volume 2: primate evolution and human origins. Berlin: Springer; 2007. p. 921–77.Google Scholar
- Begun DR. Dryopithecins, Darwin, de Bonis, and the European origin of the African apes and human clade. Geodiversitas. 2009;31:789–816.Google Scholar
- Begun DR, Kordos L. Phyletic affinities and functional convergence in Dryopithecus and other Miocene and living hominids. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997. p. 291–316.Google Scholar
- Begun DR, Ward CV. Comment on “Pierolapithecus catalaunicus, a new Middle Miocene great ape from Spain. Science. 2005;308:203c.Google Scholar
- Begun DR, Ward CV, Rose MD. Events in hominoid evolution. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997. p. 389–415.Google Scholar
- Benefit BR, McCrossin ML. Miocene hominoids and hominid origins. Ann Rev Anthropol. 1995;24:237–56.Google Scholar
- Benefit BR, McCrossin ML. Middle Miocene hominoid origins. Science. 2000;287:2375a.Google Scholar
- Biegert J. The evaluation of characters of the skull, hands and feet for primate taxonomy. In: Washburn SL, editor. Classification and human evolution. Chicago: Aldine; 1963. p. 116–45.Google Scholar
- Bishop WW, Miller JA, Fitch FJ. New potassium–argon age determinations relevant to the Miocene fossil mammal sequence in East Africa. Am J Sci. 1969;267:669–99.Google Scholar
- Boschetto HB, Brown FH, McDougall I. Stratigraphy of the Lothidok Range, Northern Kenya, and K/Ar Ages of its Miocene primates. J Hum Evol. 1992;22:47–71.Google Scholar
- Brunet M, Guy F, Pilbeam D, Taisso Mackaye H, Likius A, Ahounta D, et al. A new hominid from the Upper Miocene of Chad, central Africa. Nature. 2002;418:145–51.Google Scholar
- Caccone A, Powell JR. DNA divergence among hominoids. Evolution. 1989;43:925–42.Google Scholar
- de Bonis L, Koufos GD. Our ancestors’ ancestor: Ouranopithecus is a Greek link in human ancestry. Evol Anthropol. 1994;3:75–83.Google Scholar
- de Bonis L, Koufos G. The phylogenetic and functional implications of Ouranopithecus macedoniensis. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997. p. 317–26.Google Scholar
- de Bonis L, Koufos GD. Phylogenetic relationships of Ouranopithecus macedoniensis (Mammalia, Primates, Hominoidea, Hominidae) of the late Miocene deposits of Central Macedonia. In: de Bonis L, Koufos GD, Andrews P, editors. Hominoid evolution and climatic change in Europe, volume 2: phylogeny of the Neogene hominoid primates of Eurasia, vol. 2. Cambridge: Cambridge University Press; 2001. p. 254–68.Google Scholar
- Dean D, Delson E. Second gorilla or third chimp? Nature. 1992;359:676–7.Google Scholar
- Eckhardt RB. Population genetics and human origins. Sci Am. 1972;226:94–103.Google Scholar
- Eckhardt RB. Gigantopithecus as a hominid ancestor. Anthropol Anz. 1973;34:1–8.Google Scholar
- Eckhardt RB. Gigantopithecus as a hominid. In: Tuttle RL, editor. Paleoanthropology, morphology and paleoecology. The Hague: Mouton; 1975. p. 105–27.Google Scholar
- Frayer D. Gigantopithecus and its relationship to Australopithecus. Am J Phys Anthropol. 1973;39:413–26.Google Scholar
- Gebo DL, MacLatchy L, Kityo R, Deino A, Kingston J, Pilbeam D. A hominoid genus from the Early Miocene of Uganda. Science. 1997;276:401–4.Google Scholar
- Goodman M, Tagle DA, Fitch DH, Bailey W, Czelusniak J, Koop BF, et al. Primate evolution at the DNA level and a classification of hominoids. J Mol Evol. 1990;30:260–6.Google Scholar
- Harcourt-Smith WEH, Aiello LC. Fossils, feet and the evolution of human bipedal locomotion. J Anat. 2004;204:403–16.Google Scholar
- Harrison T. A reassessment of the phylogenetic relationship of Oreopoithecus bambolii Gervais. J Hum Evol. 1986;15:541–83.Google Scholar
- Harrison T. The phylogenetic relationships of the early catarrhine primates: a review of the current evidence. J Hum Evol. 1987;16:41–80.Google Scholar
- Harrison T. A taxonomic revision of the small catarrhine primates from the Early Miocene of East Africa. Folia Primatol. 1988;50:59–108.Google Scholar
- Harrison T. A reassessment of the taxonomic and phylogenetic affinities of the fossil catarrhines from fort Ternan, Kenya. Primates. 1992;33:501–22.Google Scholar
- Harrison T. Cladistic concepts and the species problem in hominoid evolution. In: Martin L, Kimbel W, editors. Species, species concepts, and primate evolution. New York: Plenum; 1993. p. 345–71.Google Scholar
- Harrison T. Late Oligocene to Middle Miocene catarrhines from Afro–Arabia. In: Hartwig W, editor. The primate fossil record. Cambridge: Cambridge University Press; 2002. p. 311–38.Google Scholar
- Harrison T. The zoogeographic and phylogenetic relationships of early catarrhine primates in Asia. Anthropol Sci. 2005;113:43–51.Google Scholar
- Harrison T. Apes among the tangled branches of human origins. Nature. 2010;327:532–4.Google Scholar
- Harrison T, Rook L. Enigmatic anthropoid or misunderstood ape: the phylogenetic status of Oreopithecus bambolii reconsidered. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997. p. 327–62.Google Scholar
- Harzhauser M, Piller WE. Benchmark data of a changing sea—palaeogeography, palaeobiogeography and events in the Central Paratethys during the Miocene. Palaeogeogr Palaeoclimatol Palaeoecol. 2007;253:8–31.Google Scholar
- Heizmann E, Begun DR. The oldest European hominoid. J Hum Evol. 2001;41:465–81.Google Scholar
- Hill A, Ward S. Origin of the hominidae: the record of African large hominoid evolution between 14 my and 4 my. Yrbk Phys Anthropol. 1988;32:48–83.Google Scholar
- Hill A, Leakey M, Kingston JD, Ward S. New cercopithecoids and a hominoid from 12.5 Ma in the Tugen Hills Succession, Kenya. J Hum Evol. 2002;42:75–93.Google Scholar
- Hunt KD, Cant JGH, Gebo DL, Rose MD, Walker SE, Youlatos D. Standardized descriptions of primate locomotor and postural modes. Primates. 1996;37:363–87.Google Scholar
- Ishida H, Pickford M. A new Late Miocene hominoid from Kenya: Samburupithecus koptalami gen. et Sp. Nov. C R Acad Sci Ser D. 1997;325:823–9.Google Scholar
- Ishida H, Kunimatsu Y, Nakatsukasa M, Nakano Y. New hominoid genus from the Middle Miocene of Nachola, Kenya. Anthropol Sci. 1999;107:189–91.Google Scholar
- Johnson Jr AE. Skeletal estimates of Gigantopithecus based on a gorilla analogy. J Hum Evol. 1979;8:585–7.Google Scholar
- Jolly CJ. The seed-eaters: a new model of hominid differentiation based on a baboon analogy. Man. 1970;5:5–26.Google Scholar
- Kelley J. Paleobiological and phylogenetic significance of life history in Miocene hominoids. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997. p. 173–208.Google Scholar
- Kelley J. Hominoid evolution and climate change in Europe: phylogeny of the Neogene hominoid primates of Eurasia. In: de Bonis L, Koufos GD, Andrews P, editors. Hominoid Evolution and Climatic Change in Europe, Phylogeny of the Neogene Hominoid Primates of Eurasia, vol. 2. Cambridge: Cambridge University Press; 2001. p. 269–71.Google Scholar
- Kelley J, Ward S, Brown B, Hill A, Downs W. Middle Miocene hominoid ancestors. Science. 2000;287:2375A.Google Scholar
- Kelley J, Andrews P, Alpagut B. A new hominoid species from the Middle Miocene site of Paşalar, Turkey. J Hum Evol. 2008;54:455–79.Google Scholar
- Köhler M, Moyà Solà S. Ape-like or hominid-like? The positional behavior of Oreopithecus bambolii reconsidered. Proc Natl Acad Sci USA. 1997;94:11747–50.Google Scholar
- Köhler M, Moyà Solà S, Alba DM. Eurasian hominoid evolution in the light of recent Dryopithecus findings. In: de Bonis L, Koufos GD, Andrews P, editors. Hominoid evolution and climatic change in Europe, volume 2: phylogeny of the Neogene hominoid primates of Eurasia, vol. 2. Cambridge: Cambridge University Press; 2001. p. 193–212.Google Scholar
- Kordos L, Begun DR. A new cranium of Dryopithecus from Rudabánya, Hungary. J Hum Evol. 2001;41:689–700.Google Scholar
- Kunimatsu Y, Ishida H, Nakatsukasa M, Nakano Y, Sawada Y. Maxillae and associated gnathodental specimens of Nacholapithecus kerioi, a large-bodied hominoid from Nachola, Northern Kenya. J Hum Evol. 2004;46:365–400.Google Scholar
- Kunimatsu Y, Nakatsukasa M, Sawada Y, Sakai T, Hyodo M, Hyodo H, et al. A new Late Miocene great ape from Kenya and its implications for the origins of African great apes and humans. Proc Natl Acad Sci USA. 2007;104:19220–5.Google Scholar
- Leakey LSB. A new lower pliocene fossil primate from Kenya. Ann Mag Nat Hist. 1962;13:689–96.Google Scholar
- Leakey MG, Feibel CS, McDougall I, Walker AC. New four-million-year-old species from Kanapoi and Allia Bay, Kenya. Nature. 1995;376:565–71.Google Scholar
- MacLatchy L. The oldest ape. Evol Anthropol. 2004;13:90–103.Google Scholar
- MacLatchy L, Gebo D, Kityo R, Pilbeam D. Postcranial functional morphology of Morotopithecus bishopi, with implications for the evolution of modern ape locomotion. J Hum Evol. 2000;38:159–83.Google Scholar
- MacLatchy L, Deino A, Kingston J. An updated chronology for the Early Miocene of NE Uganda. J Vertebr Paleontol Abstr Pap. 2006;26(3):93A.Google Scholar
- McBrearty S, Jablonski NG. First fossil chimpanzee. Nature. 2005;437:105–8.Google Scholar
- McCrossin ML, Benefit BR. Maboko Island and the evolutionary history of the Old World monkeys and apes. In: Corruccini RS, Ciochon RL, editors. Integrative paths to the past. Upper Saddle River: Prentice Hall; 1994. p. 95–122.Google Scholar
- McCrossin ML, Benefit BR. On the relationships and adaptations of Kenyapithecus, a large-bodied hominoid from the Middle Miocene of Eastern Africa. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997. p. 241–67.Google Scholar
- McNulty KP. Geometric morphometric analyses of extant and fossil hominoid craniofacial morphology. Unpublished PhD thesis, City University of New York;2003.Google Scholar
- McNulty KP. A geometric morphometric assessment of the hominoid supraorbital region: affinities of the Eurasian Miocene hominoids Dryopithecus, Graecopithecus, and Sivapithecus. In: Slice D, editor. Modern morphometrics in physical anthropology. New York: Kluwer; 2005. p. 349–73.Google Scholar
- Moyà-Solà S, Köhler M. Recent discoveries of Dryopithecus shed new light on evolution of great apes. Nature. 1993;365:543–5.Google Scholar
- Nakatsukasaa M, Ward CV, Walker A, Teaford MF, Kunimatsu Y, Ogihara N. Tail loss in Proconsul heseloni. J Hum Evol. 2004;46:777–84.Google Scholar
- Olejniczak AJ, Begun DR, Mbua E, Hublin J-J. Phyletic affinities of Samburupithecus kiptalami: an Upper Miocene proconsulid. Am J Phys Anthropol S. 2009;48:202.Google Scholar
- Pan Y. Lufengpithecus hudiensis site. In: Qi G, Dong W, editors. State Key Projects of the 9th Five Year Plan—Origin of Early Humans and Environmental Background, Series Monograph II. Beijing: Science Press; 2006. p. 320–2.Google Scholar
- Peppe DJ, McNulty KP, Cote SM, Harcourt-Smith WEH, Dunsworth HM, Van Couvering JA. Stratigraphic interpretation of the Kulu Formation (Early Miocene, Rusinga Island, Kenya) and its implications for primate evolution. J Hum Evol. 2009;56:447–61.Google Scholar
- Pickford M, Andrews P. The Tinderet Miocene sequence in Kenya. J Hum Evol. 1981;10:1–33.Google Scholar
- Pickford M, Kunimatsu Y. Catarrhines from the Middle Miocene (ca. 14.5 Ma) of Kipsaraman, Tugen Hills, Kenya. Anthropol Sci. 2005;113:189–224.Google Scholar
- Pilbeam D. Gigantopithecus and the origin of Hominidae. Nature. 1970;225:516–9.Google Scholar
- Pilbeam DR. Research on Miocene hominoids and hominid origins: the last three decades. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997. p. 13–28.Google Scholar
- Pilbeam DR, Young N. Hominoid evolution: synthesizing disparate data. C R Palevol. 2004;3:305–21.Google Scholar
- Raaum RL, Sterner KN, Noviello CM, Stewart C-B, Disotell TR. Catarrhine primate divergence dates estimated from complete mitochondrial genomes: concordance with fossil and nuclear DNA evidence. J Hum Evol. 2005;48:237–57.Google Scholar
- Rae TC. The early evolution of the hominoid face. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997. p. 59–77.Google Scholar
- Rae TC. Mosaic evolution in the origin of the Hominoidea. Folia Primatol. 1999;70:125–35.Google Scholar
- Rae TC. Miocene hominoid craniofacial morphology and the emergence of great apes. Ann Anat. 2004;186:417–22.Google Scholar
- Rink WJ, Wei W, Bekken D, Jones HL. Geochronology of Ailuropoda–Stegodon fauna and Gigantopithecus in Guangxi Province, Southern China. Quat Res. 2008;69:377–87.Google Scholar
- Robinson JT, Steudel K. Multivariate discriminant analyses of dental data bearing on early hominid affinities. J Hum Evol. 1973;2:509–28.Google Scholar
- Rögl F. Palaeogeographic considerations for Mediterranean and Paratethys seaways (Oligocene to Miocene). Ann Naturhist Mus Wien. 1998;99:279–310.Google Scholar
- Rook L, Bondioli L, Köhler M, Moyà Solà S, Macchiarelli R. Oreopithecus was a bipedal ape after all: evidence from the iliac cancellous architecture. Proc Natl Acad Sci USA. 1999;96:8795–9.Google Scholar
- Rose MD. Miocene hominoid postcranial morphology: monkey-like, ape-like, neither, or both? In: Ciochon RL, Corrucci RS, editors. New interpretations of ape and human ancestry. New York: Plenum; 1983. p. 405–17.Google Scholar
- Rose MD. Another look at the anthropoid elbow. J Hum Evol. 1988;17:193–224.Google Scholar
- Rose MD. Kinematics of the trapezium–1st metacarpal joint in extant anthropoids and Miocene hominoids. J Hum Evol. 1992;22:255–6.Google Scholar
- Rose MD. Functional anatomy of the elbow and forearm in primates. In: Gebo DL, editor. Postcranial adaptation in nonhuman primates. DeKalb: Northern Illinois University Press; 1993. p. 70–95.Google Scholar
- Rose MD. Quadrupedalism in some miocene catarrhines. J Hum Evol. 1994;26:387–411.Google Scholar
- Rose MD. Functional and phylogenetic features of the forelimb in Miocene hominoids. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997. p. 79–100.Google Scholar
- Ruvolo M. Molecular phylogeny of the hominoids: inferences from multiple independent DNA sequence data sets. Mol Biol Evol. 1997;14:248–65.Google Scholar
- Ruvolo M, Pan D, Zehr S, Goldberg T, Disotell TR, von Dornum M. Gene trees and hominoid phylogeny. Proc Natl Acad Sci USA. 1994;91:8900–4.Google Scholar
- Sanders WJ, Bodenbender BE. Morphometric analysis of lumbar vertebra UMP 67-28: implications for spinal function and phylogeny of the Miocene Moroto hominoid. J Hum Evol. 1994;26:203–37.Google Scholar
- Senut B. The earliest putative hominids. In: Henke W, Rothe H, Tattersall I, editors. Handbook of palaeoanthropology, volume 2: primate evolution and human origins. Berlin: Springer; 2007. p. 1519–38.Google Scholar
- Senut B, Pickford M, Gommery D, Mein P, Kiptalam C, Coppens Y. First hominid from the Miocene (Lukeino Formation, Kenya). C R Acad Sci Paris. 2001;332:137–44.Google Scholar
- Simpson JA, Weiner, ESC editors. Oxford English Dictionary, Second Edition. Oxford: Clarendon;1989.Google Scholar
- Stewart C-B, Disotell TR. Primate evolution: in and out of Africa. Curr Biol. 1998;8:582–8.Google Scholar
- Suwa G, Kono RT, Katoh S, Asfaw B, Beyene Y. A new species of great ape from the Late Miocene Epoch in Ethiopia. Nature. 2007;448:921–4.Google Scholar
- Szalay FS, Delson E. Evolutionary history of the primates. New York: Academic; 1979.Google Scholar
- Thorpe SKS, Holder RL, Crompton RH. Origin of human bipedalism as an adaptation for locomotion on flexible branches. Science. 2007;316:1328–31.Google Scholar
- Vekua A, Lordkipanidze D, Bukhsianidze M, Vanishvili N, Chagelishvili R. Importance of Diliska vertebrate fauna for the biostratigraphy of South Caucasus. Bull Georg Natl Acad Sci. 2009;3:130–5.Google Scholar
- von Koenigswald GHR. Miocene Cercopithecoidea and Oreopithecoidea from the Miocene of East Africa. Fossil Vertebr Afr. 1969;1:39–52.Google Scholar
- von Linnaeus C. Systema Naturae, Tenth Edition. New York: Weldon & Wesley;1759. p. 1384.Google Scholar
- Walker AC, Rose M. Some hominoid vertebrae from the Miocene of Uganda. Nature. 1968;217:980–1.Google Scholar
- Wang W. New discoveries of Gigantopithecus blacki teeth from Chuifeng cave in the Bubing Basin, Guangxi, South China. J Hum Evol. 2009;57:229–40.Google Scholar
- Ward CV. Functional anatomy and phyletic implications of the hominoid trunk and hindlimb. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997a. p. 101–30.Google Scholar
- Ward S. The taxonomy and phylogenetic relationships of Sivapithecus revisited. In: Begun DR, Ward CV, Rose MD, editors. Function, phylogeny and fossils: Miocene hominoid evolution and adaptations. New York: Plenum; 1997b. p. 269–90.Google Scholar
- Ward S, Brown B. The facial skeleton of Sivapithecus indicus. In: Swindler DR, Erwin J, editors. Comparative primate biology. New York: Alan R. Liss; 1986. p. 413–52.Google Scholar
- Ward SC, Duren DL. Middle and Late Miocene African hominoids. In: Hartwig W, editor. The Primate Fossil Record. Cambridge: Cambridge University Press; 2002. p. 385–97.Google Scholar
- Ward SC, Kimbel WH. Subnasal alveolar morphology and the systemic position of Sivapithecus. Am J Phys Anthropol. 1983;61:157–71.Google Scholar
- Ward SC, Pilbeam DR. Maxillofacial morphology of Miocene hominoids from Africa and Indo-Pakistan. In: Corruccini RL, Ciochon RS, editors. New interpretations of ape and human ancestry. New York: Plenum; 1983. p. 211–38.Google Scholar
- Ward CV, Walker A, Teaford MF. Proconsul did not have a tail. J Hum Evol. 1991;21:215–20.Google Scholar
- Ward S, Brown B, Hill A, Kelley J, Downs W. Equatorius: a new hominoid genus from the Middle Miocene of Kenya. Science. 1999;285:1382–6.Google Scholar
- Weidenreich F. Apes, giants and man. Chicago: University of Chicago Press; 1946.Google Scholar
- White TD, Suwa G, Asfaw B. Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia. Nature. 1994;371:306–12.Google Scholar
- White TD, Asfaw B, Beyene Y, Haile-Selassie Y, Lovejoy CO, Suwa G, et al. Ardipithecus ramidus and the paleobiology of early hominids. Science. 2009;326:75–86.Google Scholar
- Wunderlich RE, Walker A, Jungers WL. Rethinking the positional repertoire of Oreopithecus. Am J Phys Anthropol. 1999;108:528.Google Scholar
- Xu X, Delson E. A new species of Dryopithecus from Gansu, China. Kexue Tongbao. 1988;33:449–53.Google Scholar