A key specimen of the human story, its position on our family tree is highly debated. Is it the oldest known hominin or should it be placed on the tree before the human line split from the line leading to chimpanzees?
Background of discovery
6.1 to 5.8 million years ago
Important fossil discoveries
A handful of fossil fragments, from five individuals, were found in Kenya in 2000 during excavations by the Kenya Palaeontology Expedition (KPE)under Martin Pickford of the KPE and Brigitte Senut from the Museum of Natural History, Paris. The discovery was published in 2001. The remains include several limb bones, jaw fragments and isolated teeth. The holotype specimens are 2 mandible fragments, BAR1000a’00 and BAR1000b’00. An isolated lower molar (KNM LU 335), that may belong to this species, was discovered in this area in 1974.
What the name means
The genus name Orrorin means ‘original man’ in the Tugen language, whereas the species name tugenensis was assigned because the fossils were found in the Tugen Hills of Kenya.
Fossils have been found at four sites (Cheboit, Kapsomin, Kapcheberek, and Aragai) in the Tugen Hills, Kenya
Relationships with other species
Its discoverers believe this species belongs on the human family tree. They claim that it is dissimilar to the genus Australopithecus, and that this genus should be moved to a side branch on the human tree, leaving Orrorin tugenensis as the earliest direct ancestor of humans. This is contrary to the beliefs of a vast majority of palaeoanthropologists and there is not enough evidence to support the argument due to the fragmentary nature of the remains. Other experts think this species may have lived before the ape and human line split so could be an ancestor of both lines or that it was a basal member of the hominin clade.
The species lived during a critical period in the human evolutionary timeline. It is widely believed human and chimps diverged from a common ancestor that lived between five and eight million years ago.
Key physical features
- probably similar in size to a modern chimpanzee, but lack of cranial material makes this difficult to determine
Body size and shape
- uncertain, probably similar in size to a modern chimpanzee
- some features of the leg bones indicate this species was possibly bipedal. The femur was different from that of modern humans, fossil Homo and living apes and most closely resembled australopithecines that lived three to four million years ago.
- some features of the leg bones are found in non-bipedal primates, suggesting that this species may not be bipedal. At the moment the evidence is inconclusive.
- features of the arms bones (humerus) and a curved finger bone suggest it was also adapted for climbing tree
Jaws and teeth
- primitive dental anatomy
- teeth have thick enamel and are relatively small, although canines are relatively large and pointed compared to humans
There is no evidence for any specific cultural attributes. However, it may have used simple tools similar to those used by modern chimpanzees including:
- twigs, sticks and other plant materials that were easily shaped or modified. These may have been used for a variety of simple tasks including obtaining food.
- unmodified stones, that is stones that were not shaped or altered before being used. These tools may have been used to process hard foods such as nuts.
Environment and diet
When this species lived, the environment was open woodland with dense tree forests.
The large, flat molars suggest a diet of fruit and vegetables, but it may have also been an opportunistic meat eater.
Pickford, M. and Senut, B. (2001). 'Millennium ancestor', a 6-million-year-old bipedal hominid from Kenya. South African Journal of Science 97. 1-2: 22.
Senut, Brigitte; Martin Pickford; Dominique Gommery; Pierre Mein; Kiptalam Cheboi; Yves Coppens (2001). First hominid from the Miocene (Lukeino Formation, Kenya). Comptes Rendus de l'Academie des Sciences, Series IIA - Earth and Planetary Science 332. 2 (30 January 2001): 137-144
Michael Balter, Scientists Spar Over Claims of Earliest Human Ancestor, Science 291, 5508 (23 Feb 2001): 1460-1461