The Earliest Hominoids
Hominoid fossils are known throughout much of the Miocene in Africa and Eurasia, with the earliest specimens of a species
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FICURE 16.2 Proconsul africanus: This reconstruction is based on fossils found prior to 1959 (colored) by Mary Leakey and in 1980, among the Nairobi Museum collections, by Alan Walker and Martin Pickford. This individual, a young female that lived approximately 18 million years ago, has characteristics of both modern monkeys (in its long trunk and arm and hand bones) and modern apes (in its shoulder, elbow, cranial, and dental characteristics). (Courtesy of Alan Walker.)
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FICURE 16.2 Proconsul africanus: This reconstruction is based on fossils found prior to 1959 (colored) by Mary Leakey and in 1980, among the Nairobi Museum collections, by Alan Walker and Martin Pickford. This individual, a young female that lived approximately 18 million years ago, has characteristics of both modern monkeys (in its long trunk and arm and hand bones) and modern apes (in its shoulder, elbow, cranial, and dental characteristics). (Courtesy of Alan Walker.)
of Proconsul (dated at approximately 22 million years) coming from Africa, the likely region of origin for the clade. Although claims have been put forth for an even earlier Proconsul specimen, at 26 million years, their validity cannot be established because of the absence of reliably diagnostic parts. In any case, the hominoid clade apparently originated some time between 31 and 22 million years ago.
FICURE 16.3 Miocene apes: These faces of African apes, which lived some 18 million years ago, illustrate the diversity of morphology among Miocene apes. (Courtesy of John Fleagle/ Academic Press.)
Hominoids underwent several adaptive radiations, producing a great abundance and variety of species that followed lifestyles not typical of modern apes (see figures 16.2 and 16.3). Proconsul itself produced several species, including one as small as a gibbon and another the size of a female gorilla. Miocene hominoids were creatures of tropical and subtropical forests. Climate change—the result of global cooling and local tectonic activity— greatly reduced hominoid habitat through the late Miocene in the Old World and was probably responsible for the drop in the diversity of hominoids. Cer-copithecoid diversity increased in parallel with this change, and many monkey species came to occupy niches previously filled by hominoids.
It is worth repeating that the postcranial anatomy of extant hominoids—adaptations to a suspensory habit—evolved only recently; it is not seen in any fossil apes to any great degree. Most Miocene apes more closely resemble monkeys in terms of their posture and locomotion. We will begin with a description of Proconsul, which many consider to be the basal hominoid, before describing the archaic and modern hom-inoid radiations. (See figure 16.4.)
Proconsul fossils have been found at several sites in Kenya, and this species is probably the best-known Miocene ape. In its cranial and dental features, Proconsul is judged to be primitive; the thin enamel layer on its cheek teeth apparently reflects a nonhominoid origin. The brain was relatively large, and the increased surface area of the molars and broadening of the incisors imply a more frugivorous diet. In its post-cranial skeleton, Proconsul displays a mix of ape and monkey features. For instance, although it had no tail (like an ape), its thorax was narrow and deep, a characteristic seen in pronograde (body horizontal to the ground) monkeylike locomotion rather than orthograde (body more vertical to the ground) apelike locomotion. "In the forelimb skeleton, the shoulder and elbow region are remarkably apelike," notes Alan Walker of Pennsylvania State University, "but the arm and hand bones look more like those of some monkeys. In the hindlimb the reverse is true: the foot and lower leg bones are very apelike while the hip region looks less so." Proconsul would have moved more like a monkey than like the forelimb-dominated ape in terms of posture and locomotion. Interestingly, the hand had a large, opposable thumb, which makes Proconsul more like humans than either monkeys or apes. This feature suggests that Proconsul might have
Turkanapithecus
Micropithecus
Turkanapithecus
Micropithecus
Afropithecus
Proconsul
Afropithecus
Proconsul
FICÜRE 16.5 Sivapithecus: This 8-million-year-old specimen of Sivapithecus indicus comes from the Potwar plateau in Pakistan. The animal was roughly the same size as a chimpanzee but had the facial morphology of an orangutan; it ate soft fruit (detected in the toothwear pattern) and was probably mainly arboreal. (Courtesy of David Pilbeam.)
FICURE 16.4 Rusinga Island in the early Miocene: This community of apes, living 18 million years ago, illustrates something of the species diversity that would later become the characteristic of monkeys. Upper left, Proconsul africanus; upper right, Dendropithecus macinnesi; center, Limnopithecus legetet; lower, Proconsulnyanzae. (Courtesy of John Fleagle/Academic Press.)
FICURE 16.4 Rusinga Island in the early Miocene: This community of apes, living 18 million years ago, illustrates something of the species diversity that would later become the characteristic of monkeys. Upper left, Proconsul africanus; upper right, Dendropithecus macinnesi; center, Limnopithecus legetet; lower, Proconsulnyanzae. (Courtesy of John Fleagle/Academic Press.)
had considerable manipulative skills, perhaps including making and using simple tools, such as stripped twigs.
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