Orrorin

Orrorin
Temporal range: Late Miocene, 6.1–5.7 Ma
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Orrorin tugenensis fossils
The distal phalanx of the thumb.
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Order:Primates
Suborder:Haplorhini
Infraorder:Simiiformes
Family:Hominidae
Subfamily:Homininae
Tribe:Hominini
Genus:†Orrorin
Senut et al. 2001
Species: †O. tugenensis
Binomial name
Orrorin tugenensis

Orrorin tugenensis is a postulated early species of Homininae, estimated at 6.1 to 5.7 million years (Ma) and discovered in 2000. It is not confirmed how Orrorin is related to modern humans. Its discovery was an argument against the hypothesis that australopithecines are human ancestors, as much as it still remains the most prevalent hypothesis of human evolution as of 2012.[1]

The name of genus Orrorin (plural Orroriek) means "original man" in Tugen,[2][3] and the name of the only classified species, O. tugenensis, derives from Tugen Hills in Kenya, where the first fossil was found in 2000.[3] As of 2007, 20 fossils of the species have been found.[4]

Fossils

The 20 specimens found as of 2007 include: the posterior part of a mandible in two pieces; a symphysis and several isolated teeth; three fragments of femora; a partial humerus; a proximal phalanx; and a distal thumb phalanx.[4]

Orrorin had small teeth relative to its body size. Its dentition differs from that found in Australopithecus in that its cheek teeth are smaller and less elongated mesiodistally and from Ardipithecus in that its enamel is thicker. The dentition differs from both these species in the presence of a mesial groove on the upper canines. The canines are ape-like but reduced, like those found in Miocene apes and female chimpanzees. Orrorin had small post-canines and was microdont, like modern humans, whereas robust australopithecines were megadont.[4]

In the femur, the head is spherical and rotated anteriorly; the neck is elongated and oval in section and the lesser trochanter protrudes medially. While these suggest that Orrorin was bipedal, the rest of the postcranium indicates it climbed trees. While the proximal phalanx is curved, the distal pollical phalanx is of human proportions and has thus been associated with toolmaking, but should probably be associated with grasping abilities useful for tree-climbing in this context.[4]

After the fossils were found in 2000, they were held at the Kipsaraman village community museum, but the museum was subsequently closed. Since then, according to the Community Museums of Kenya chairman Eustace Kitonga, the fossils are stored at a secret bank vault in Nairobi.[5]

Physical features  

The shaft of a human femur (thigh bone) is a very strong cylinder, adapted to the heavy loading of bipedal walking. In Orrorin tugenensis,The femur has particularly thick bone in the upper part of the shaft—evidence for bipedalism. The shape of the upper arm bone and the slightly curved finger, however, indicates that the upper limbs were weight bearing too. The pointed canine tooth, low cusped molars, and large upper front tooth may reflect a diet of fruit and seeds. Taken together, this could imply a mixed arboreal and terrestrial lifestyle[6].  

Classification

If Orrorin proves to be a direct human ancestor, then australopithecines such as Australopithecus afarensis ("Lucy") may be considered a side branch of the hominid family tree: Orrorin is both earlier, by almost 3 million years, and more similar to modern humans than is A. afarensis. The main similarity is that the Orrorin femur is morphologically closer to that of H. sapiens than is Lucy's; there is, however, some debate over this point.[7]

Other fossils (leaves and many mammals) found in the Lukeino Formation show that Orrorin lived in a dry evergreen forest environment, not the savanna assumed by many theories of human evolution.[7]

Discovery

In 1974, a fossil molar tooth was unearthed by paleontologist Martin Pickford from late Miocene deposits at Cheboit, Kenya. With low cusps on the chewing surface and thick enamel, it did not fit into any known species. Pickford named it Orrorin tugenensis the following year, but it was nearly 30 years until the next major find. A French–Kenyan team led by Pickford and French paleontologist Brigitte Senut returned to the region and in 2001 announced the discovery of teeth and fragments of the arms and legs of several individuals. This species may have been one of the earliest members of the human lineage to walk upright[6] .

The team that found these fossils in 2000 was led by Brigitte Senut and Martin Pickford[2] from the Muséum national d'histoire naturelle. The 20 fossils have been found at four sites in the Lukeino Formation, located in Kenya: of these, the fossils at Cheboit and Aragai are the oldest (6.1 Ma), while those in Kapsomin and Kapcheberek are found in the upper levels of the formation (5.7 Ma).[4]

See also

Notes

  1. ↑ Reynolds, Sally C; Gallagher, Andrew (2012-03-29). African Genesis: Perspectives on Hominin Evolution. ISBN 9781107019959.
  2. 1 2 Senut et al. 2001
  3. 1 2 Haviland et al. 2007, p. 122
  4. 1 2 3 4 5 Henke 2007, pp. 1527–9
  5. ↑ "Whereabouts of fossil treasure sparks row". Daily Nation. May 19, 2009. Retrieved December 1, 2010.
  6. 1 2 "Alice Roberts - Evolution The Human Story - 2011.pdf". Google Docs. Retrieved 2018-10-13.
  7. 1 2 Pickford 2001, Interview

References

  • CogWeb. "Orrorin Tugenensis: Pushing back the hominin line". UCLA. Retrieved December 1, 2010.
  • Haviland, William A.; Prins, Harald E. L.; Walrath, Dana; McBride, Bunny (2007). Evolution and prehistory: the human challenge. Cengage Learning. ISBN 0-495-38190-X.
  • Henke, Winfried (2007). Henke, Winfried; Hardt, Thorolf; Tattersall, Ian, eds. Handbook of paleoanthropology: Phylogeny of hominids. Springer. pp. 1527–9. ISBN 978-3-540-32474-4.
  • Pickford, Martin (December 2001). "Martin Pickford answers a few questions about this month's fast breaking paper in field of Geosciences". Essential Science Indicators.
  • Senut, Brigitte; Pickford, Martin; Gommery, Dominique; Mein, Pierre; Cheboi, Kiptalam; Coppens, Yves (2001). "First hominid from the Miocene (Lukeino Formation, Kenya)" (PDF). Comptes Rendus de l'Académie des Sciences. 332 (2): 137–144. Bibcode:2001CRASE.332..137S. doi:10.1016/S1251-8050(01)01529-4. Archived from the original (PDF) on February 26, 2014. Retrieved November 1, 2012.
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