Overview

Brief Summary

Nickname: Millenium Man

Where Lived: Eastern Africa (Tugen Hills, central Kenya)

When Lived: Sometime between 6.2 and 5.8 million years ago

Living around 6 million years ago, Orrorin tugenensis is the one of the oldest early humans on our family tree. Individuals of this species were approximately the size of a chimpanzee and had small teeth with thick enamel, similar to a modern human’s. The most important fossil of this species is an upper femur, showing evidence of bone buildup typical of a biped - so Orrorin tugenensis individuals climbed trees but also probably walked upright with two legs on the ground.

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Physical Description

Size

Orrorin’s thigh bone (femur) and upper arm bone (humerus) are about 1.5 times larger than those of Lucy’s (AL 288-1). Therefore, scientists estimate that Orrorin would have been 1.5 times larger than A. afarensis, suggesting a size similar to a female chimpanzee, between about 30 and 50 kg.

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Type Information

Key Fossils

BAR 1002'00

Site: Tugen Hills, Kenya

Date of discovery: 2001

Discovered by: A team led by Brigitte Senut and Martin Pickford

Age: About 6 million years old

Species: Orrorin tugenensis

Beginning to walking upright on short legs

The upper part of this thigh bone (femur) is similar in size to those of other large apes. But the angled part more closely resembles that of modern humans. It formed a strong bridge with the hip to support the body’s weight, suggesting Orrorin tugenensis walked upright.

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Life History and Behavior

Behavior

How They Survived

From their low, rounded molars and small canine teeth, paleoanthropologists can infer that Orronin ate mainly a plant-based diet. This probably included leaves, fruit, seeds, roots, nuts, and insects.

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Evolution and Systematics

Evolution

Evolutionary Tree Information

Orrorin is at the base of the human family tree, and has more ape-like features than human-like ones -- except that it walked upright on two legs.

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Fossil History

History of Discovery

Year of Discovery: 2001

A research team led by French paleontologist Brigitte Senut and French geologist Martin Pickford discovered this species in the Tugen Hills region of central Kenya. They found more than a dozen early human fossils dating between about 6.2 million and 6.0 million years old. Because of its novel combination of ape and human traits, the researchers gave a new genus and species name to these fossils, Orrorin tugenensis, which in the local language means “original man in the Tugen region.” So far, Orrorin tugenensis is the only species in the genus Orrorin.

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Wikipedia

Orrorin

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[edit]

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 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 Australopithecenes 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 this 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]

Classification[edit]

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. [6]

Other fossils (leaves and many mammals) found in the Lukeino Formation show that Orrorin lived in dry evergreen forest environment, not the savanna assumed by many theories of human evolution.[6]

Discovery[edit]

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 discoverers conclude that Orrorin is a hominin on the basis of its bipedal locomotion and dental anatomy; based on this, they date the split between hominins and African great apes to at least 7 million years ago, in the Messinian. This date is markedly different from those derived using the molecular clock approach, but has found general acceptance among paleoanthropologists.

The 20 fossils have been found at four sites in the Lukeino Formation: 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[edit]

Notes[edit]

  1. ^ Reynolds, Sally C; Gallagher, Andrew (2012-03-29). African Genesis: Perspectives on Hominin Evolution. ISBN 9781107019959. 
  2. ^ a b Senut et al. 2001
  3. ^ a b Haviland et al. 2007, p. 122
  4. ^ a b c d e Henke 2007, pp. 1527–9
  5. ^ "Whereabouts of fossil treasure sparks row". Daily Nation. May 19, 2009. Retrieved December 2010. 
  6. ^ a b Pickford 2001, Interview

References[edit]

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Notes

The Unknown

We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas with groundbreaking technology, and continually filling in some of the gaps about our understanding of human evolution.

Below are some of the still unanswered questions about Orrorin tugenensis that may be answered with future discoveries:

1. Is Orrorin a direct human ancestor to Homo sapiens? If so, does this make A. afarensis a side branch of our of hominin family tree that eventually hit a dead-end?

2. Did Orrorin routinely walk on two legs? Orrorin’s fossil evidence indicates that Orrorin was possibly capable of bipedalism, but not necessarily that Orrorin routinely walked bipedal.

3. How did bipedalism originate? One hypothesis suggests early apes walked on branches while using their arms for balance and this technique eventually made its way to the ground.

4. What is the relationship between this species and Sahelanthropus tchadensis, the other current contender for the title of earliest human?

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