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Prior to the year 2000, the dominant paradigms of hominid origins could be summarised as follows: (a) the African ape/human (AAH) dichotomy occurred about 5 Ma, perhaps 6 Ma for some authors, or as young as 2.5 Ma for others; (b) the precursors of hominids were probably quadrupedal, terrestrial apes; (c) the AAH transition likely took place in the savannah; (d) the last common ancestor (LCA) of African apes and humans looked like a chimpanzee (prolonged face, enlarged canines in males, knuckle-walking locomotion and black body coats); and (e) there was an australopithecine stage between the LCA and the genus Homo.
The discovery of the 6 million-year-old bipedal hominid Orrorin in the Lukeino Formation, Kenya, in 2000, and in particular its femora, which showed that it was fully bipedal, was bound to pose serious challenges to all these paradigms. Given that Orrorinis almost twice as old as Lucy (AL 288–01, Australopithecus antiquus, which is possibly a species different from Australopithecus afarensis in which it is usually classified) (Ferguson, 1984) and almost 2 million years older than Ardipithecus ramidus ramidus, it would be surprising if it didn’t upset the apple cart to some extent. Further studies in the Lukeino Formation reveal that most previous ideas concerning remote hominid origins need to be modified or refined. Not only their biological aspects, but also their chronological and environmental aspects require rethinking.
Martin Pickford, Laboratoire de Paleontologie, UMR 8569 du CNRS, 8, rue Buffon, 75005, Paris College de France, 11, Place Marcellin Berthelot, 7505, Paris, France,
Brigitte Senut, Département Histoire de la Terre, USM 0203, du Muséum National d'Histoire naturelle & UMR 5143, PICS 1048 (CNRS), Case 38, 57, rue Cuvier, 75005, Paris, France
This paper deals with some of the implications of the discovery of four ape-like teeth from the Middle Miocene (12,5 Ma) and Late Miocene (6–5,9 Ma) of Kenya. An unworn, isolated lower molar from Member B of the Ngorora Formation (12,5 Ma), Tugen Hills, Kenya, differs markedly from lower molars of Middle and Early Miocene large hominoids but is closer in morphology to chimpanzee molars (peripheralised cusps, buccolingually compressed lingual cusps, thin enamel, large and deep occlusal basin, reduced buccal cingulum). If the tooth is part of the chimpanzee clade then it is important for estimating the timing of the dichotomy between chimpanzees and hominids and suggests that this event would have occurred several million years earlier than is currently estimated by most researchers.
An incomplete, unworn isolated upper molar, an upper central incisor and a lower molar from the Lukeino Formation (6–5,9 Ma), Tugen Hills, Kenya, are morphologically closer to those of Gorilla gorilla than to any other fossil or extant hominoid with which they were compared. The upper molar is a large tooth (mesio-distal length 14 mm) with peripheralised cusps, bucco-lingually wide distal fovea, fairly voluminous trigon basin and high dentine penetrance, all features which suggest affinities with gorillas. Its enamel thickness (1,6–1,7 mm on the hypocone) is similar to that of gorilla molars. It differs markedly from molars of the early hominid, Orrorin tugenensis, which occurs at the same site, which are smaller, have more centralised cusps, smaller trigon basin, reduced distal fovea and low dentine penetrance. The Kapsomin molar differs from teeth of australopithecines for much the same reasons, even if its dimensions overlap with those of Australopithecus antiquus and Praeanthropus africanus. It is highly divergent from chimpanzee teeth, not only in its dimensions, but also in its morphology. An upper central incisor from Kapsomin is large and wedge-shaped in lateral view without the lingual fossa that characterises teeth of hominids and chimpanzees. It is close in size and morphology to those of gorillas.
If the species from which the Kapsomin and Cheboit teeth came is part of the gorilla clade, then there are important implications for the timing of events in gorilline evolution, and they make it less likely that European genera such as Ouranopithecus are ancestral to African apes or hominids.
A re-examination of the lectotype of Sus giganteus Falconer & Cautley, 1847, reveals that it is a suine, as originally thought by its discoverers, and not a tetraconodont as recently published. It may belong to the genus Propotamochoerus as proposed by Azzaroli in 1989. This reassessment radically modifies tetraconodont systematics published recently by Van der Made (1999).
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