, Volume 46, Issue 1, pp 21–32 | Cite as

Incisor-molar relationships in chimpanzees and other hominoids: implications for diet and phylogeny

  • Martin Pickford
Original Article


In chimpanzees, the cutting edge of the incisor battery is longer in relation to the length of the molar row than in any other hominoid, extant or fossil, the only other lineage approaching it being the orangutan. Apart from their increased mesio-distal dimensions, the upper and lower incisors of chimpanzees differ in additional ways from those of almost all other hominoids. The I2/ is enlarged, so that the difference in size between it and the central upper incisor is less than it is in the heteromorphic upper incisors of other hominoids. The lower incisors are expanded mesio-distally, so much so that isolated I/2 crowns can resemble upper central incisors. In chimpanzees the lingual surface of the lower incisors is generally more procumbent than it is in other hominoids, which have more vertically oriented incisor crowns and there is a greater difference in enamel thickness between labial and lingual sides. The re-orientation of the lower incisor crown is reflected in the root, which in lateral view is anteriorly concave in chimpanzees whereas it is more orthogonal or convex in other hominoids. The molars of chimpanzees, especially the lowers, have extensive and relatively deep occlusal basins, and the main cusps are peripheralised and labio-lingually compressed, making them more trenchant than those of other hominoids. This paper examines the incisor-lower molar proportions in extinct and living hominoids and develops a new hypothesis about the evolution of the dentition of chimpanzees and links it to their diet. It also examines the incisor-molar proportions of hominids and African apes in order to throw light on the phylogenetic relationships between them. It is shown that chimpanzees are highly derived in this respect and that several recent ideas concerning the chimp-like appearance of the last common ancestor of hominids and African apes are likely to be incorrect.


Hominoidea Incisors Molars Meat-eating Phylogeny 



I thank members of the Kenya Palaeontology Expedition for their help in the field, in particular Dr. Brigitte Senut and Mr. Kiptalam Cheboi. Research permission was accorded by the Ministry of Education, Research and Technology, Kenya. Funds were provided by the Collège de France (Prof. Y. Coppens), the Laboratoire de Paléontologie (Prof. P. Taquet), the French Ministry of Foreign Affairs (Commission de Fouilles) and the CNRS (Projet PICS). I am particularly keen to thank the Community Museums of Kenya (Mr. E. Gitonga) for their help and cooperation and Prof. H. Ishida for inviting me to spend time in his laboratory as visiting professor at Kyoto University. I also thank the Primate Research Institute, Inuyama, and Dr. T. Nishida, Kyoto University for access to collections in their care.


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Copyright information

© Japan Monkey Centre and Springer-Verlag 2005

Authors and Affiliations

  1. 1.Département Histoire de la Terre, UMR 5143 CNRSParisFrance
  2. 2.Collège de FranceParisFrance

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