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''Orrorin tugenensis'' is a postulated early species of
Homininae Homininae (), also called "African hominids" or "African apes", is a subfamily of Hominidae. It includes two tribes, with their extant as well as extinct species: 1) the tribe Hominini (with the genus ''Homo'' including modern humans and numerou ...
, estimated at and discovered in 2000. It is not confirmed how ''Orrorin'' is related to
modern humans Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
. Its discovery was used to argue against the hypothesis that
australopithecine Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally ''Australopithecus'' ( cladistically including the genera ''Homo'', '' Paranthropus'', and ''Kenyanthropus''), and it typically inclu ...
s are human ancestors, although this remains the most prevalent hypothesis of
human evolution Human evolution is the evolutionary process within the history of primates that led to the emergence of '' Homo sapiens'' as a distinct species of the hominid family, which includes the great apes. This process involved the gradual developmen ...
as of 2012. The name of genus ''Orrorin'' (plural ''Orroriek'') means "original man" in Tugen, and the name of the only classified species, ''O. tugenensis'', derives from Tugen Hills in
Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...
, where the first
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
was found in 2000. As of 2007, 20 fossils of the species have been found.


Fossils

The 20 specimens found as of 2007 are believed to be from at least five individuals. They include: the posterior part of a
mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
in two pieces; a symphysis and several isolated teeth; three fragments of femora; a partial
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a r ...
; a proximal
phalanx The phalanx ( grc, φάλαγξ; plural phalanxes or phalanges, , ) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar pole weapons. The term is particularly ...
; and a distal thumb phalanx. ''Orrorin'' had small teeth relative to its body size. Its dentition differs from that found in ''
Australopithecus ''Australopithecus'' (, ; ) is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genus ''Homo'' (which includes modern humans) emerged within ''Australopithecus'', as sister to e.g. ''Australo ...
'' in that its
cheek teeth Cheek teeth or post-canines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate (having many folds or tubercles). Mammals have multicuspidate molars (three in placentals, four in marsupials, in each jaw quadrant) and p ...
are smaller and less elongated mesio
distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
ly 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 australopithecines were megadont. However, some researchers have denied that this is compelling evidence that ''Orrorin'' was more closely related to modern humans than australopithecines as early members of the genus ''Homo'', who were almost certainly the direct ancestors of modern humans, were also megadonts. In the femur, the
head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals ...
is spherical and rotated anteriorly; the
neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...
is elongated and oval in section and the
lesser trochanter The lesser trochanter is a conical posteromedial bony projection of the femoral shaft. it serves as the principal insertion site of the iliopsoas muscle. Structure The lesser trochanter is a conical posteromedial projection of the shaft of the fe ...
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. 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. More recently, in 2017, impressions resembling human-like footprints were reported on the island of
Crete Crete ( el, Κρήτη, translit=, Modern: , Ancient: ) is the largest and most populous of the Greek islands, the 88th largest island in the world and the fifth largest island in the Mediterranean Sea, after Sicily, Sardinia, Cyprus, ...
in Greece. These " Trachilos footprints", found in fossilized beach sediments near the west Cretan village of Trachilos, have been dated to a similar time period as the ''Orrorin'' fossils, 6.05 million years before present. However, there is no consensus that these impressions are distinct enough to confidently assign to a primate or even a
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...
, or that they are indeed footprints at all.


Classification

If ''Orrorin'' proves to be a direct human ancestor, then according to some paleoanthropologists,
australopithecine Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally ''Australopithecus'' ( cladistically including the genera ''Homo'', '' Paranthropus'', and ''Kenyanthropus''), and it typically inclu ...
s such as ''
Australopithecus afarensis ''Australopithecus afarensis'' is an extinct species of australopithecine which lived from about 3.9–2.9 million years ago (mya) in the Pliocene of East Africa. The first fossils were discovered in the 1930s, but major fossil finds would no ...
'' ("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 ''
Homo sapiens Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture ...
'' than is ''Lucy's''; there is, however, some debate over this point. This debate is largely centered around the fact that Lucy was female and the ''Orrorin'' femur it has been compared to belonged to a male. Another point of view cites comparisons between Orrorin and other
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
apes, rather than extant great apes, which shows instead that the femur shows itself as an intermediate between that of Australopiths and said earlier apes. Other fossils (leaves and many mammals) found in the Lukeino Formation show that ''Orrorin'' lived in a dry evergreen forest environment, not the
savanna A savanna or savannah is a mixed woodland- grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground ...
assumed by many theories of
human evolution Human evolution is the evolutionary process within the history of primates that led to the emergence of '' Homo sapiens'' as a distinct species of the hominid family, which includes the great apes. This process involved the gradual developmen ...
.


Evolution of bipedalism

The fossils of ''Orrorin tugenensis'' share no derived features of hominoid great-ape relatives. In contrast, "''Orrorin'' shares several apomorphic features with modern humans, as well as some with australopithecines, including the presence of an ''obturator externus'' groove, elongated femoral neck, anteriorly twisted head (posterior twist in ''Australopithecus''), anteroposteriorly compressed femoral neck, asymmetric distribution of cortex in the femoral neck, shallow superior notch, and a well developed gluteal tuberosity which coalesces vertically with  the  crest  that  descends  the  femoral  shaft  poste-riorly." It does, however, also share many of such properties with several Miocene ape species, even showing some transitional elements between basal apes like the
Aegyptopithecus ''Aegyptopithecus'' ("Egyptian ape", from Greek ''Αίγυπτος'' "Egypt" and ''πίθηκος'' "ape") is an early fossil catarrhine that predates the divergence between hominoids ( apes) and cercopithecids (Old World monkeys). It is kno ...
and Australopithecus. According to recent studies ''Orrorin tugenensis'' is a basal hominid that adapted an early form of bipedalism. Based on the structure of its femoral head it still exhibited some arboreal properties, likely to forage and build shelters. The length of the femoral neck in ''Orrorin tugenensis'' fossils is elongated and is similar in shape and length to ''Australopithicines'' and modern humans. While it was originally claimed that its femoral head is larger in comparison to ''Australopithicines'' and is much closer in shape and relative size to ''Homo sapiens'', this claim has been challenged by some researchers who have noted that the femoral heads of male australopithicines are more akin to those of ''Orrorin'', and by extension modern humans, than those of female australopithicines. Proponents of the notion that Orrorin is more closely related to humans than Lucy is have addressed this by asserting that the male australopithicine femurs in question in fact belong to a different species than Lucy. O. tugenensis appears to have developed bipedalism 6 million years ago. ''O. tugenensis'' shares an early hominin feature in which their iliac blade is flared to help counter the torque of their body weight, this shows that they adapted bipedalism around 6 MYA. These features are shared with many species of ''Australopithecus''. It has been suggested by Pickford that the many features ''Orrorin'' shares with modern humans show that it is more closely related to ''Homo'' ''sapiens'' than to ''Australopithecus''. This would mean that Australopithecus would represent a side branch in the homin evolution that does not directly lead to ''Homo''. However the femora morphology of ''O. tugenensis'' shares many similarities with ''Australopithicine'' femora morphology, which weakens this claim. Another study conducted by Almecija suggested that ''Orrorin'' is more closely related to early hominins than to ''Homo''. An analysis of the BAR 10020' 00 femur showed that ''Orrorin'' is an intermediate between ''Pan'' and ''Australopithecus afarensis''. The current prevailing theory is that ''Orrorin tugenensis'' is a basal hominin and that bipedalism developed early in the hominin clade and successfully evolved down the human evolutionary tree. It is clear that the phylogeny of ''Orrorin'' is uncertain, however, the evidence of the evolution of bipedalism is an invaluable discovery from this early fossil hominin.


Discovery

The team that found these fossils in 2000 was led by
Brigitte Senut Brigitte Senut (27 January 1954, Paris) is a French paleoprimatologist and paleoanthropologist and a professor at the National Museum of Natural History, Paris. She is a specialist in the evolution of great apes and humans. Life and work Senu ...
and Martin Pickford from the
Muséum national d'histoire naturelle The French National Museum of Natural History, known in French as the ' (abbreviation MNHN), is the national natural history museum of France and a ' of higher education part of Sorbonne Universities. The main museum, with four galleries, is loc ...
. 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 (), while those in Kapsomin and Kapcheberek are found in the upper levels of the formation ().


See also

* List of human evolution fossils ''(with images)'' * Martin Pickford


Notes


References

* * * * *


External links


Orrorin tugenensis
- The Smithsonian Institution's Human Origins Program
Human Timeline (Interactive)
Smithsonian,
National Museum of Natural History The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. In 2021, with 7. ...
(August 2016). {{Taxonbar, from=Q311630 Homininae Miocene primates of Africa Fossil taxa described in 2001 Prehistoric Kenya Baringo County Articles containing video clips Taxa named by Martin Pickford