New specimens and confirmation of an early age for Australopithecus anamensis

Abstract

The discovery of Australopithecus anamensis fossils from strata lying between tephra dated at 4.17 and 4.12 million years ago, and from slightly higher strata not well constrained in age by overlying dated units, provoked the claim that more than one species might be represented: it was suggested that the stratigraphically higher fossils, which include the important tibia, humerus and a large, presumed male, mandible (KNM-KP 29287), might belong to a later, more derived hominid. We have recovered new fossils from Kanapoi and Allia Bay, Kenya, during field work in 1995-1997 that confirm the primitive status of Australopithecus anamensis, the earliest species of Australopithecus. Isotope dating confirms A. anamensis' intermediate age as being between those of Ardipithecus ramidus and Australopithecus afarensis. New specimens of maxilla, mandible and capitate show that this species is demonstrably more primitive than A. afarensis. A lower first deciduous molar (dm 1) is intermediate in morphology between that reported for Ardipithecus ramidus and A. afarensis. Single-crystal 40Ar-39Ar age determinations on the Kanapoi Tuff show that, except for a large mandible, all of the hominid fossils from Kanapoi are from sediments deposited between 4.17+/-0.03 and 4.07+/-0.02 million years ago.

A multidisciplinary reconstruction of Palaeolithic nutrition that holds promise for the prevention and treatment of diseases of civilisation

“…1) are Sahelanthropus tchadensis from Chad (about 7 Mya (65) ) and Orrorin tugenensis from Kenya (about 6-5·7 Mya (66) ). The next oldest are Ardipithecus kadabba (Ethiopia, about 5·8 Mya (67) ) and A. ramidus (Ethiopia, about 4·4 Mya (68) ), Australopithecus anamensis (Kenya, about 4·1-3·9 Mya (69) ), Au. afarensis (Ethiopia, Tanzania and maybe Kenya, 3·6 -3·0 Mya (70,71) ), Au.…”

Placing confidence limits on the molecular age of the human–chimpanzee divergence

“…As recently as the mid-1960s (2), the African apes were considered to be distant relatives of the human lineage, but subsequent molecular phylogenetic analyses have shown that the chimpanzee and human are sister species and have led to a revision of the age of their divergence (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Currently, the earliest unequivocal upright hominids at 4.2 millions of years ago (Ma) provide the minimum age for human-chimpanzee divergence (14), and some recently proposed early hominids dated between 5 and slightly more than 6 Ma are thought to provide an estimate close to the actual species divergence (15)(16)(17)(18)(19). However, a divergence time of 12.5 Ma for humans and chimpanzees has been entertained recently as well (20), and so the fossil record and its interpretation give a range of 4.2-12.5 Ma.…”

Evolution of Human Parental Behavior and the Human Family

“…The degree of sexual dimorphism in A. anamensis and A. afarensis suggests intense one-onone male -male competition and perhaps a gorilla-like social structure (Leakey et al, 1998). Although other social structures are, of course, possible (Plavcan, 2000), a gorilla-like social structure is consistent with many features of human social organization.…”

“…Males and females of monogamous species, in contrast, tend to be similar in physical size (e.g., Leigh, 1995). When these patterns are compared to patterns of sexual dimorphism in the fossil record, inferences about the reproductive strategies of extinct hominids can be drawn (Foley, 1999;Leakey, Feibel, McDougall, & Walker, 1995;Leakey, Feibel, McDougall, Ward, & Walker, 1998).…”

“…For australopithecine species dating from about 4 million years ago, including A. afarensis and A. anamensis, males are estimated to have weighed from 60% to 100% more than females (e.g., Leakey et al, 1998;Ward, Leakey, & Walker, 1999). By, and perhaps with, the emergence of H. erectus about 1½ to 2 million years ago (Stringer, 1992), males were estimated to be about 20% heavier than females -a difference that is similar to what is seen in human beings today (McHenry, 1994a;Richmond & Jungers, 1995).…”