Earlyape evolution

In the lower Miocene of East Africa (24-16 Myr ago), apes were more abundant than anywhere today. A typical early form is Proconsul (Walker et al., 1983; Walker and Teaford, 1989). The genus was named in 1933 on the basis of some jaws and teeth from Kenya, and the name refers to a chimp named Consul who then lived at London Zoo and entertained visitors with his bicycle riding and pipe smoking. Since the 1930s, evidence of most of the skeleton has been found, including several well-preserved associated skeletons (Figure 11.4).

Proconsul has a long monkey-like trunk and the arm and hand bones share the characters of modern monkeys and apes. Many different modes of locomotion have been proposed, ranging from nearly fully bipedal walking (when it was thought to be closer to human ancestry), through knuckle walking, as seen in modern chimps and gorillas, to full brachiation,swinging hand over hand through the trees as in modern gibbons. The present view is that Proconsul could move on the ground on all fours and run quadrupedally along heavy branches. The elbow and foot anatomy of Proconsul is fully apelike, but the head is primitive, with small molar teeth

Fig. 11.4 Miocene apes: (a, b) Proconsul skeleton (a) and skull (b). [Figure (a) after A. Walker, in Lewin, 1999, courtesy of Blackwell Scientific Publications Ltd; (b) modified from Walker et al., 1983.]

and long projecting canines (Figure 11.4(b)). Its diet was probably soft fruit.

Proconsul is regarded as a true ape because it shows a number of derived characters shared with the modern forms, such as the absence of a tail and the relatively large brain size (150 cm3). In addition, Proconsul shows a number of other ape-like characters of the teeth and modifications to strengthen the elbow joint for brachiation.

The story of ape evolution continued in Africa during the mid- and late Miocene (16-5 Myr ago),but some lines branched off and evolved separately in Europe and Asia. The gibbons, four species of Hylobates,are the most primitive of living apes, and they appear to have branched off the line to the great apes, the Hominidae,in the early Miocene,but no fossils are known.

11.3.2 Hominidae: evolution in Africa, Europe and Asia

The living Hominidae fall into two subfamilies, the Ponginae,the orang-utan and its fossil relatives, and the Homininae, chimps, gorillas, humans and their fossil relatives (see Box 11.3). This split marks a divergence in modes of locomotion from a generalized tree-climbing ancestor: the orangs specialized in suspension (brachia-tion) and slow climbing, whereas the African great apes specialized in terrestrial quadrupedalism (chimps, gorilla) and bipedalism (humans).

The first hominids may be the Kenyapithecinae, known mainly from eastern Africa, but also from Turkey, central Europe and perhaps Namibia, from 20 to 14 Myr ago. Kenyapithecus, named on the basis of

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