AFRICAN APE ANCESTRY
Hum.Evol.5: 295-297, 1990

It is commonly believed that the australopithecines are more closely related to humans than to African apes. This view is hardly compatible with the bio-molecular data, which place the Homo/Pan split at the beginning of the australopithecine period.
Nothing in the fossil hominid morphology precludes the possibility that some australopithecines were ancestral to gorillas or chimpanzees, and others to humans.

It is commonly thought that from a period covering at least the last 4 million years, no fossils of ancestors of the African apes have been found so far, although 100s of hominid fossils have been discovered from that period. The usual explanation for
this remarkable absence of fossil apes is low fossilisation probability in tropical forests (where the ancestral apes presumably lived).
A more likely solution is that not only man, but also the African apes have descended from the australopithecines (e.g. Gribbin & Cherfas 1983, Hasegawa cs 1985, Edelstein 1987). The molecular clock leaves little doubt that the man/chimp split occurred
between 6 & 4 Ma (Hasegawa cs 1985), which is in the beginning of the australopith period from c 6 (Lukeino, Lothagam) until 1 Ma (Taung).
Australopithecines are generally believed to be closer to man than to apes because of their dental & locomotor features. Like man, they have much thicker molar enamel than apes, but enamel thickness has been secondarily reduced in the African apes (
Martin 1987). The robust forms show much smaller anterior teeth than the adult males of G.gorilla & P.troglodytes (differences with the females are less). But bonobos have rather small & only slightly dimorphic canine teeth (Zihlman cs 1978). Since the
prognathism of Negroes vs other humans developed in c 200,000 yrs (Cann cs 1987), the evolution of the (indeed much more pronounced) ape prognathism in 1 Myr cannot be considered impossible.
The human-like orientations of afarensis, distal femoral & tibial articulations (Stern & Susman 1983), the short iliac bones of Lucy & A.africanus (McHenry 1982) & the more central foramen magnum in the robust australopiths & Taung are thought to be
correlated with bipedality. However, Gribbin & Cherfas (1983), Hasegawa cs (1985) & Edelstein (1987) have argued that the African apes’ ancestors were more bipedal. Also bonobos have a more central foramen (Kimbel cs1984) and frequently walk
bipedally (Zihlman cs 1978).
The mistake of many palaeo-anthropologists - the anthropocentric fallacy using «primitive» for «gorilla-» or «chimp-like» - is described by Hasegawa cs (1985): «It seems to have been widely assumed implicitly that the common ancestor (of man &
chimp) was more like the chimpanzee».

Cranial resemblances between australopithecines & apes are listed in Table 1. Also «the Homo like features of Australopithecine limb bones tend to have been greatly exaggerated in the literature (OJ Lewis pers.comm.). Most afarensis postcranials (AL-
288, -129, -333) are different from both humans & apes, but the scapula, humerus, ulna, knee, hand & foot bones are more like apes (McHenry 1982, Stern & Susman 1983, Senut 1981, Feldesman 1982, Tardieu 1986, Sarmiento 1987, Deloison 1985).
Lucy’s pelvic girdle AL-288 resembles the apes in some respects (lateral enlargement of iliac blades, small auricular & acetabular articulation surfaces, small lumbo-sacral angle: McHenry 1982, Stern & Susman 1983, Abitbol 1987), and her upper limb
looks rather bonobo-like (Stern & Susman 1983, Feldesman 1982). Also A.africanus scapula Sts 7 (McHenry 1982), its hand bones (TM 1526) & those of A.robustus (SKW 14147, SK 84 & 85) are more chimp- than humanlike (Lewis 1977). The enormous L40-19 ulna
of A.boisei is of gorilla size, and morphologically intermediate between man & common chimp (Feldesman 1982).
Although the picture is confused by the retention of ancestral characters in populations that split not very long before (e.g. large & small A.afarensis) & by parallel evolution (both robust forms lived at the same time), it gives me the following
impressions. A.boisei & perhaps some of the larger A.afarensis are closer to Gorilla, while Lucy & the S.African australopiths show more affinities with Homo-Pan (but A.robustus, living at the time of KNM-ER-1470, could not belong to the Homo lineage).
The Taung child, which lived even later than A.robustus, is perhaps ancestral to Pan paniscus or to Pan troglodytes.

Table l - Cranial resemblances of australopiths with apes

• The australopith dentition is more apelike in development pattern (Conroy & Vannier 1987), enamel growth rate (Bromage & Dean 1985), dental morphology (Johanson & Edey 1981) & enamel microwear.
• All australopithecine brain-endocasts appear to be ape- rather than humanlike in size & sulcal pattern (Falk 1985).
• The composite A.afarensis skull (mostly AL 333: Kimbel cs 1984) «looked very much like a small female gorilla» (Johanson & Edey 1981).
• The extensive pneumatization of the AL-333-45 temporal bone is also seen in chimpanzee males & some gorillas; «the pattern of pneumatization in A.afarensis is also found only in the extant apes among other hominoids» (Kimbel cs 1984).
• KNM-WT-17000 had «extremely convex infero-lateral margins of the orbits such as found in some gorillas» (Walker cs 1986).
• «The ‘keystone’ nasal bone arrangement suggested as a derived pattern diagnostic of Paranthropus is found in an appreciable number of pongids, particularly clearly in some chimpanzees» (Eckhardt 1987).
• A.robustus incus SK 848 resembles Pan more than Homo, and certainly than Gorilla (Fig.1 in Rak & Clarke, 1979).
• A.africanus Sts-5 resembles a bonobo skull (Zihlman cs 1978).
• The Taung skull has much more chimp- than human traits (Bromage 1985) and is indeed much too recent (Partridge 1985) to be on the line to Homo.
• Its «pneumatization has also extended into the zygoma & hard palate. This is intriguing because an intra-palatal extension of the maxillary sinus has only been reported in chimpanzees & robust australopithecines among higher primates» (Conroy &
Vannier 1987).

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