Praeanthropus Lucy and her relations

Basal hominins flourished in the Pliocene. In a change from previous terminology, most of these humans have now been referred to Praeanthropus, a little-known genus established in 1948 for a jaw fragment from the Pliocene of Kenya. The various species have been shown to form a monophyletic group by Strait et al. (1997), Wood and Collard (1999) and Cameron (2003) that is distinct from Australopithecus proper (see below). Cela-Conde and Ayala (2003) also include Orrorin within Praeanthropus. These technical disputes have to be sorted out!

Leakey et al. (1995) reported an ancient hominin, Praeanthropus anamensis, from sediments 4.1 to 3.9Myr old near Lake Turkana in Kenya, that appears to be an intermediate beween Ardipithecus and later species. The remains include jaws, a humerus, a tibia and isolated teeth. It has a primitive jaw with a shallow palate and large canines. The tibia shows, however, that P. anamensis was a biped.

The most complete skeleton of a Mio-Pliocene hominin, Praeanthropus afarensis, was discovered by Donald Johanson and colleagues in Ethiopia in 1974. The skeleton was from a young female, nicknamed Lucy, which consisted of 40% of the bones, unusually complete by usual standards (Figure 11.9(b)). Some

240 specimens were found at Hadar in the 1970s and 50 new specimens have been found in the 1990s, including a good skull (Kimbel et al., 1994). Lucy is dated as 3.2 Myr old and P. afarensis specimens range from 3.2 to 2.9 Myr in age. Further specimens from Laetoli in Tanzania are dated as 3.6-3.7 Myr old. These include some bones and the famous trackway of bipedal footprints.

Praeanthropus afarensis individuals are 1-1.2 m tall, with a brain size of only 415 cm3 and a generally ape-like face. Other primitive characters include the presence of a small diastema (Figure 11.9(c)), long arms and rather short legs and curved finger and toe bones (Figure 11.9(d-f)). These curved bones imply that Lucy still used her hands and feet in grasping branches, as apes do. In addition, there are specializations in the wrist, which suggest that P. afarensis (and P. anamensis) had evolved from a not-too-distant knuckle-walking ancestor (Richmond and Strait, 2000), a specialized mode of locomotion retained today by chimps and gorillas. Praeanthropus afarensis is human, though, in some significant ways: the tooth row is somewhat rounded (Figure 11.9(c)) and hindlimbs and pelvis are fully

Fig. 11.9 The australopiths: (a) the lower canine, premolars and molars ofthe chimpanzee Pan troglodytes (top), Ardipithecus ramidus (middle) and Praeanthropus afarensis (bottom); (b) skeleton of'Lucy', the oldest reasonably complete hominid, P. afarensis; (c) palate of 'Lucy'; fingers of (d) an ape, (e) Australopithecus and (f) a modern human, showing the loss of curvature, used for grasping branches; the hindlimbs of (g) an ape, (h) P. afarensis and (i) a modern human, showing changes in pelvic shape, limb bone length and angle. [Figure (a) based on White et al., 1994; (b) modified from photographs; (c, g-i) after Lewin, 1999, courtesy ofBlackwell Scientific Publications Ltd; (d-f) adapted from Napier, 1962,© 1962 by Scientific American, Inc. All rights reserved.]

Fig. 11.9 The australopiths: (a) the lower canine, premolars and molars ofthe chimpanzee Pan troglodytes (top), Ardipithecus ramidus (middle) and Praeanthropus afarensis (bottom); (b) skeleton of'Lucy', the oldest reasonably complete hominid, P. afarensis; (c) palate of 'Lucy'; fingers of (d) an ape, (e) Australopithecus and (f) a modern human, showing the loss of curvature, used for grasping branches; the hindlimbs of (g) an ape, (h) P. afarensis and (i) a modern human, showing changes in pelvic shape, limb bone length and angle. [Figure (a) based on White et al., 1994; (b) modified from photographs; (c, g-i) after Lewin, 1999, courtesy ofBlackwell Scientific Publications Ltd; (d-f) adapted from Napier, 1962,© 1962 by Scientific American, Inc. All rights reserved.]

adapted for a type of bipedal locomotion (Figure 11.9(g-i)). The fuller collections now available show that P. afarensis was a sexually dimorphic species, with males having jaws 30% larger than females.

A further hominin fossil is Kenyanthropus platyops from 3.5-Myr-old rocks in Kenya (Leakey et al., 2001), based on a relatively complete cranium. The face is flatter than in P. afarensis and the skull differs in further details, although White (2003) suggests this is most likely a distorted specimen of P. afarensis,whereas Cela-Conde and Ayala (2003) retain the species as valid,but as a tentative member of Homo—quite a divergence of opinion!

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