Orrorin

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Orrorin
Orrorin tugenensis.jpg

Orrorin

Temporal occurrence
Upper Miocene
6.2 to 5.65 million years
Locations
Systematics
Human (Hominoidea)
Apes (Hominidae)
Homininae
Hominini
Orrorin
Scientific name
Orrorin
Senut , Pickford et al., 2001
species
  • Orrorin tugenensis

Orrorin is an extinct species of primates , in the upper Miozän in Kenya occurred. Their fossil remains have been dated to an age of around 6 million years. Orrorin is probably close to the genera Ardipithecus and Sahelanthropus and, like these, is attributed tothe Australopithecines by many researchers. Since the individuals of Orrorin tugenensis could probably walk upright , the genus was placed by its discoverers at the base of the ancestral line of the hominini ; However, because of the few, fragmentary finds, this is controversial.

Naming

The name of the genus is derived from the word orrorin , which means “primitive man, fossil” in the language of the virtues ; the epithet of the only scientifically described species so far, Orrorin tugenensis , refers to the place of discovery, the Tugen Hills in the Baringo district in Kenya. Orrorin tugenensis therefore means "primitive man from Tugen". Because it was discovered in 2000, the only species in the genus so far , Orrorin tugenensis , is also known as "Millennium Man".

The fossils are kept in the Kenyan National Museum in Nairobi.

Terminal (phalanx distalis) of the thumb of the chimpanzee , gorilla , orrorin , human and Homo habilis . Arrows mark morphological features from which the ability to grip with precision was derived.

Initial description

According to the first scientific description from 2001, the holotype of the genus and also the type species Orrorin tugenensis are two related lower jaw fragments with three molars (archive number BAR 1000a'00 and BAR 1000b'00; BAR stands for the Kenyan district of Baringo), the Kiptalam Cheboi discovered in October 2000. They were assigned a molar that Martin Pickford had already recovered in 1974 in the Tugen Hills near the town of Cheboit, 250 km west of Nairobi , and scientifically described along with other finds the following year.

Another five teeth not associated with the lower jaw were discovered, a finger bone, a fragment of a right humerus and three fragments of a femur ; later the end link of a finger was added.

These finds were recovered from four different deposits, so that their assignment to a single species is not mandatory; the finger bone (BAR 349'00), for example, comes from a find layer that is possibly more than 300,000 years younger than the layers of the other finds. The tooth finds also come from layers of different ages, but at least suggest that they came from a living being that mainly fed on plants. Since rocks of volcanic origin are stored both above and below them, the age of the find layers could be reliably dated between 6.2 and 5.65 million years.

features

From the structure of the thigh bones, the researchers deduced that Orrorin tugenensis had walked upright. Since there is a similar thickness of the outer bone layer in baboons , this interpretation was initially very controversial. The same applied to the statement that the structure of the humerus's bones made it possible to derive the ability to carry heavy loads. On the other hand, it can be safely deduced from the size of the arm and leg bones that Orrorin tugenensis was around 50 percent larger than Lucy , the best-known hominid skeleton of the much younger species Australopithecus afarensis . In a study published in 2013 it was argued that the structure of the thigh bone had features that point to a phylogenetic position between Miocene monkeys and the Australiopthecines .

A comparison of the third member of thumb (= end member distal phalanx) of chimpanzee , gorilla , Orrorin and man yielded evidence that Orrorin also the ability to precision grip had developed.

Accompanying finds of various animal and plant species lead to the conclusion that the layers of the find originate from a habitat in which wooded areas, moist grasslands and lake shores alternate ( gallery forests ). Orrorin tugenensis could - as evidenced by the nature of its thigh bones - have lived both on the ground and in the trees.

controversy

Although the fossils have only survived in fragments and come from different sites and time horizons, their discoverers have drawn far-reaching conclusions from them. In 2001 they wrote in the South African Journal of Science, even before the fossils were classified as a new species, that their findings were “ closer to the hominids still alive today than the much younger Australopithecines and Ardipithecus ramidus in terms of size and morphology ”. They called this the extinct sidelines; Instead, they placed their own Kenyan fossil finds at the base of the line of development that ultimately led to modern man and in this way declared Kenya to be the actual cradle of humanity . A heated scientific discussion immediately broke out around these theses and is still ongoing.

A re-examination of the best preserved femur BAR1002'00 by Brian Richmond of George Washington University and William L. Jungers of Stony Brook University confirmed in March 2008 that Orrorin tugenensis could walk upright. The structure of the bone differs both from that of the great apes and that of the genus Homo ; it most closely resembles the femur of Australopithecus and Paranthropus . Computer-aided analyzes of 300 fossil and contemporary comparative pieces also showed that the biomechanics of the hip in particular are very similar to that of the australopithecines. The two researchers therefore suspect that these traits developed in the common ancestors of the species mentioned, lasted for almost four million years and were only modified in the late Pliocene - with the emergence of the genus Homo . They therefore explicitly described the find as hominin , but their analysis also supported the thesis of the majority of paleoanthropologists that the development to modern humans did not proceed directly from orrorin , but from the australopithecines.

In February 2011, Bernard Wood and Terry Harrison criticized in a review article the assignment of orrorin and Ardipithecus and Sahelanthropus to the taxon hominini as being premature. The upright gait is by no means an exclusive feature of the hominini, but also, for example, of Oreopithecus , which - like Ramapithecus punjabicus - was initially placed at the base of the hominini, but was later unequivocally classified apart from the hominini due to other features. Therefore, it cannot be ruled out that the similarity of the characteristics of orrorin with those of the oldest species, Australopithecus anamensis, which is undoubtedly considered hominin , is to be assessed as synapomorphism and indicates convergent developments .

The following year, Martin Pickford replied that Orrorin was closer to the genus Homo than Australopithecus in three separate characteristics : hand (thumb), leg (femur), and dental apparatus (tooth size and ratio).

The genera of the hominini :
The chronological sequence does not allow any conclusions to be drawn about their family relationships.

Web links

Individual evidence

  1. ↑ Brigitte Senut, Martin Pickford, Dominique Gommery, Pierre Mein, Kiptalam Cheboi, Yves Coppens : First hominid from the Miocene (Lukeino Formation, Kenya). In: Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science. Volume 332, No. 2, 2001, pp. 137–144, doi: 10.1016 / S1251-8050 (01) 01529-4 , full text (PDF)
  2. ↑ Martin Pickford : Late Miocene sediments and fossils from the Northern Kenya Rift Valley. In: Nature . Volume 256, 1975, pp. 279-284, doi: 10.1038 / 256279a0
  3. ↑ www.modernhumanorigins.net A detailed description of the finds
  4. ↑ M. Pickford, B. Senut: 'Millennium ancestor', a 6-million-year-old bipedal hominid from Kenya. In: South African Journal of Science. Volume 97, No. 1–2, 2001, p. 22, full text (PDF)
  5. ↑ Martin Pickford, Brigitte Senut, Dominique Gommery and Jacques Treil: Bipedalism in Orrorin tugenensis revealed by its femora. In: Comptes Rendus Palevol. Volume 1, No. 4, 2002, pp. 191-203, doi: 10.1016 / S1631-0683 (02) 00028-3
  6. ↑ Ann Gibbons: Oldest Human Femur Wades Into Controversy. In: Science . Volume 305, 2004, p. 1885, doi: 10.1126 / science.305.5692.1885a
  7. ↑ Sergio Almécija et al .: The femur of Orrorin tugenensis exhibits morphometric affinities with both Miocene apes and later hominins. In: Nature Communications . Volume 4, item number: 2888, 2013, doi: 10.1038 / ncomms3888 , full text (PDF)
  8. ↑ Sergio Almécija, Salvador Moyà-Solà and David M. Alba: Early Origin for Human-Like Precision Grasping: A Comparative Study of Pollical Distal Phalanges in Fossil hominins. In: PLoS ONE. 5 (7): e11727. doi: 10.1371 / journal.pone.0011727
  9. ↑ Roberts, Alice .: The Beginnings of Mankind. From the upright gait to the early high cultures . Dorling Kindersley, Munich 2012, ISBN 978-3-8310-2223-6 .
  10. ^ Brian G. Richmond and William L. Jungers : Orrorin tugenensis Femoral Morphology and the Evolution of Hominin Bipedalism. In: Science. Volume 319, 2008, pp. 1662-1665, doi: 10.1126 / science.1154197
  11. ↑ Ann Gibbons: Millennium Ancestor Gets Its Walking Papers. In: Science. Volume 319, 2008, pp. 1599-1601
  12. ↑ Bernard Wood , Terry Harrison : The evolutionary context of the first hominins. In: Nature . Volume 470, 2011, pp. 347-352, doi: 10.1038 / nature09709
  13. ↑ Martin Pickford: Orrorin and the African ape / hominid dichotomy In: African Genesis. Perspectives on Hominin Evolution . Ed. Sally C. Reynolds, Andrew Gallagher, Cambridge 2012, pp. 104-108, ISBN 978-1-107-01995-9