Sahelanthropus tchadensis is an extinct hominid The Hominidae form a taxonomic family, including four extant genera: chimpanzees, gorillas, humans, and orangutans species In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are often used, such as based on similarity of DNA or that is dated to about 7 million years ago. Whether it can be regarded as part of the Hominina The more anthropomorphic primates of the Hominini tribe are placed in the Hominina subtribe. They are characterized by the evolution of an increasingly erect bipedal locomotion. The only extant species is Homo sapiens. Fossil records indicate this subtribe branched from the common ancestor with the chimpanzee lineage about 3 to 5 million years ago tree is unclear; there are arguments both supporting and rejecting it. Another complication in its classification is that it is older than the human-chimpanzee divergence (estimated to 6.3 to 5.4 million years ago) seen in genetic data,[2] and that there are few if any specimens other than the partial cranium known as Toumaï.

Contents

Fossils

Location of discovery Detail of map Restoration of the face of Sahelanthropus

Existing fossils – a relatively small cranium nicknamed Toumaï ("hope of life" in the local Dazaga language of Chad), five pieces of jaw The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals and some teeth Teeth are small, calcified, whitish structures found in the jaws (or mouths) of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and – make up a head that has a mixture of derived and primitive features. The braincase, being only 320 cm³ to 380 cm³ in volume is similar to that of extant chimpanzees and is notably less than the approximate human volume of 1350 cm³. The teeth, brow ridges, and facial structure differ markedly from those found in Homo sapiens Humans are known taxonomically as Homo sapiens , and are the only extant member of the Homo genus of bipedal primates in Hominidae, the great ape family. However, in some cases "human" is used to refer to any member of the genus Homo. Cranial features show a flatter face, u-shaped dental arcade, small canines, an anterior foramen magnum, and heavy brow ridges. No postcranial remains have been recovered. Due to the distortion that the cranium has suffered, a 3D computer reconstruction has not been produced.

Since no postcranial remains (bones below the skull) have been discovered, it is as of yet unknown whether Sahelanthropus tchadensis was indeed bipedal, although claims for an anteriorly placed foramen magnum In anatomy, in the occipital bone, the foramen magnum is one of the several oval or circular apertures in the base of the skull (the foramina), through which the medulla oblongata (an extension of the spinal cord) enters and exits the skull vault suggests that this may have been the case, some paleontologists have disputed this interpretation of the basicranium. Its canine wear is similar to other Miocene apes.[3] Moreover, according to recent information, the femur of an hominid may have been discovered alongside the cranium but never published.[4]

The fossils were discovered in the Djurab desert of Chad Chad , officially known as the Republic of Chad, is a landlocked country in central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west. Due to its distance from the sea and its largely desert climate, the country is sometimes by a team of four led by Michel Brunet; three Chadians, Adoum Mahamat, Djimdoumalbaye Ahounta and Gongdibé Fanoné, and Frenchman, Alain Beauvilain.[5][6] All known material of Sahelanthropus were found between July 2001 to March 2002 at three sites (TM 247, TM 266 which yielded most of the material, and TM 292). The discoverers claimed that S. tchadensis is the oldest known human ancestor after the split of the human line from that of chimpanzees Chimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:. The bones were found far from most previous hominin Hominini is the tribe of Homininae that comprises Humans , and two species of the genus Pan (the Common Chimpanzee and the Bonobo), their ancestors, and the extinct lineages of their common ancestor. Members of the tribe are called hominins (cf. Hominidae, "hominids"). The subtribe Hominina is the "human" branch, including fossil finds, which are from Eastern East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa: and Southern Africa Southern Africa is the southernmost region of the African continent, variably defined by geography or geopolitics. Within the region are numerous territories, including the Republic of South Africa ; nowadays, the simpler term South Africa is generally reserved for the country in English. However, an Australopithecus bahrelghazali Australopithecus bahrelghazali is a fossil hominin that was first discovered in 1993 by the paleontologist Michel Brunet in the Bahr el Ghazal valley near Koro Toro, in Chad, that Brunet named Abel. It was dated using Berylium based Radiometric dating as living circa. 3.6 million years ago mandible was found in Chad by Beauvilain A., Brunet M. and Moutaye A.H.E. as early as 1995.[7]

Relationship to modern humans and great apes

Sahelanthropus may represent a common ancestor In evolutionary biology, a group of organisms have common descent if they have a common ancestor. All living organisms on Earth are descended from a common ancestor or ancestral gene pool of humans and chimpanzees; no consensus has been reached yet by the scientific community. The original placement of this species as a human ancestor but not a chimpanzee ancestor would complicate the picture of human phylogeny In biology, phylogenetics is the study of evolutionary relatedness among various groups of organisms , which is discovered through molecular sequencing data and morphological data matrices. The term phylogenetics is of Greek origin from the terms phyle/phylon (φυλή/φῦλον), meaning "tribe, race," and genetikos (γενετικός. In particular, if Toumaï is a direct human ancestor, then its facial features bring the status of Australopithecus Australopithecus is a genus of hominids that are now extinct. From the evidence gathered by palaeontologists and archaeologists, it appears that the Australopithecus genus evolved in eastern Africa around 4 million years ago before spreading throughout the continent and eventually becoming extinct 2 million years ago. During this time period, into doubt because its thickened brow ridges were reported to be similar to those of some later fossil hominids (notably Homo erectus), whereas this morphology differs from that observed in all australopithecines, most fossil hominids and extant humans.

Another possibility is that Toumaï is related to both humans and chimpanzees, but is the ancestor of neither. Brigitte Senut and Martin Pickford, the discoverers of Orrorin tugenensis Orrorin tugenensis is considered to be the second-oldest known hominin ancestor that is possibly related to modern humans, and it is the only species classified in genus Orrorin. The name was given by the discoverers who found Orrorin fossils in the Tugen Hills of Kenya. By using radiometric dating techniques, the volcanic tuffs and lavas, faunal, suggested that the features of S. tchadensis are consistent with a female proto-gorilla Gorillas are the largest of the living primates. They are ground-dwelling and predominantly herbivorous. They inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies. The DNA of gorillas is 98%–99% identical to that of a human, and they are the next closest living relatives to humans after. Even if this claim is upheld, then the find would lose none of its significance, for at present precious few chimpanzee or gorilla ancestors have been found anywhere in Africa. Thus if S. tchadensis is an ancestral relative of the chimpanzees (or gorillas) then it represents the first known member of their lineage. Furthermore, S. tchadensis does indicate that the last common ancestor of humans and chimpanzees is unlikely to resemble chimpanzees very much, as had been previously supposed by some paleontologists.[8] · [9] Unfortunately, the exact age of the fossil is somewhat hard to determine. While molecular clocks The molecular clock (based on the molecular clock hypothesis ) is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged. It is used to estimate the time of occurrence of events called speciation or radiation. The molecular data are increasingly found to be far more unreliable than initially believed[10] sediment Sediment is naturally-occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself isotope analysis Isotope analysis is the identification of isotopic signature, the distribution of certain stable isotopes and chemical elements within chemical compounds. This can be applied to a food web to make it possible to draw direct inferences regarding diet, trophic level, and subsistence. Isotope ratios are measured using mass spectrometry which which yielded an age of about 7 million years is generally considered quite reliable. In this case however, the fossils were found exposed in loose sand; co-discoverer Beauvilain cautions that such sediment can be easily moved by the wind, unlike packed earth.[11] In fact, Toumaï was probably reburied in the recent past. Taphonomic analysis reveals the likelihood of one, perhaps two, burial(s) which seemingly occurred after the introduction of Islam in the region. Two other hominid fossils (a left femur and a mandible) were in the same “grave” along with various mammal remains.The sediment surrounding the fossils might thus not be the material the bones were originally deposited in, making it necessary to corroborate the fossil's age by some other means.[12] The fauna Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna" found at the site – namely the anthracotheriid Libycosaurus petrochii and the suid Suidae is the biological family to which pigs and their relatives belong. Up to sixteen species are currently recognized, including the domestic pig Sus scrofa or S. domesticus. They are classified into between four and eight genera. In addition to numerous species of wild pig, the family includes the babirusa Babyrousa babyrussa and the warthog Nyanzachoerus syrticus – suggests an age of more than 6 million years, as these species In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are often used, such as based on similarity of DNA or were probably extinct In biology and ecology, extinction is the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species . Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena already by that time.[13]

See also

Notes

  1. ^ Usually, all authors of a taxon A taxon is a group of (one or more) organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement. Defining what belongs or does not belong to such a taxonomic group is done by a taxonomist. It is not uncommon for one taxonomist to disagree with another on what exactly belongs to description are cited. In this case they are so many however that for layout reasons the list is abbreviated. The full citation is: Brunet, Guy, Pilbeam, Mackaye, Likius, Ahounta, Beauvilain, Blondel, Bocherens, Boisserie, De Bonis, Coppens, Dejax, Denys, Duringer, Eisenmann, Fanone, Fronty, Geraads, Lehmann, Lihoreau, Louchart, Mahamat, Merceron, Mouchelin, Otero, Pelaez Campomanes, Ponce de León, Rage, Sapanet, Schuster, Sudre, Tassy, Valentin, Vignaud, Viriot, Zazzo, & Zollikofer, 2002.
  2. ^ "Evolution's human and chimp twist". BBC. May 18, 2006. http://news.bbc.co.uk/2/hi/science/nature/4991470.stm. Retrieved April 2010.
  3. ^ Brunet, Guy, Pilbeam, Mackaye, Likius, Djimdoumalbaye, Beauvilain, Blondel, Bocherens, Boisserie, De Bonis, Coppens, Dejax, Denys, Duringer, Eisenmann, Gongdibé, Fronty, Geraads, Lehmann, Lihoreau, Louchart, Adoum, Merceron, Mouchelin, Otero, Pelaez Campomanes, Ponce De Leon, Rage, Sapanet, Schuster, Sudre, Tassy, Valentin, Vignaud, Viriot, Zazzo & Zollikofer, 2002. A new hominid from the Upper Miocene of Chad, Central Africa, Nature Nature is a prominent British scientific journal, first published on 4 November 1869. It is the world's most highly cited interdisciplinary science journal. Most scientific journals are now highly specialized, and Nature is among the few journals that still publish original research articles across a wide range of scientific fields. There are many, 418 (6894): 145-151.
  4. ^ Hawks 2009 Sahelanthropus: The femur of Toumaï?
  5. ^ Tchad Actuel Toumaï : Histoire des Sciences et Histoire d’Hommes
  6. ^ Web site of Alain Beauvilain
  7. ^ Brunet M., Beauvilain A., Coppens Y., Heintz E., Moutaye A.H.E. et Pilbeam D., 1995. The first australopithecine 2,500 kilometres west of the Rift Valley (Chad) Nature, 378 (6554): 273-275. résumé]
  8. ^ Guy F., Lieberman D. E., Pilbeam D., Ponce de Leon M. S., Likius A., Mackaye H. T., Vignaud P., Zollikofer C. P. E. et Brunet M., (27 December 2005). Morphological affinities of the Sahelanthropus tchadensis (Late Miocene hominid from Chad) cranium [1] PDF fulltext Supporting Tables, PNAS, 102 (52) : 18836-18841.
  9. ^ Wolpoff M. H., Hawks J., Senut B., Pickford M. et Ahern J., 2006. An Ape or the Ape : Is the Toumaï Cranium TM 266 a Hominid?, PaleoAnthropology, 2006: 36-50.
  10. ^ Lebatard A.-E., Bourles D. L., Duringer P., Jolivet M., Braucher R., Carcaillet J., Schuster M., Arnaud N., Monie P., Lihoreau F., Likius A., Mackaye H. T., Vignaud P. et Brunet M., 2008. Cosmogenic nuclide dating of Sahelanthropus tchadensis and Australopithecus bahrelghazali: Mio-Pliocene hominids from Chad. PNAS 105(9): 3226-3231 PDF fulltext
  11. ^ Beauvilain 2008 The contexts of discovery of Australopithecus bahrelghazali and of Sahelanthropus tchadensis (Toumaï) : unearthed, embedded in sandstone or surface collected ? South african Journal of Science, 104 (3): 165-168.
  12. ^ Beauvilain and Watté, 2009. Toumaï ("Sahelanthropus tchadensis") a-t-il été inhumé ? Bulletin de la Société géologique de Normandie et des Amis du Museum du Havre, 96 (1): 19-26.
  13. ^ Brunet M., Guy F., Pilbeam D., Lieberman D. E., Likius A., Mackaye H. T., Ponce de Leon M. S., Zollikofer C. P. E. et Vignaud P., 2005. New material of the earliest hominid from the Upper Miocene of Chad. Nature, 434 (7034): 752-755

References

External links

Wikispecies Wikispecies is a wiki-based online project supported by the Wikimedia Foundation. Its aim is to create a comprehensive free content catalogue of all species and is directed at scientists, rather than at the general public. Jimmy Wales—chairman emeritus of the Wikimedia Foundation—stated that editors are not required to fax in their degrees, has information related to: Sahelanthropus
Part of the series on Human evolution Human evolution, or anthropogenesis, is the origin and evolution of Homo sapiens as a distinct species from other hominids, great apes and placental mammals. The study of human evolution encompasses many scientific disciplines, including physical anthropology, primatology, archaeology, linguistics and genetics
Hominini Hominini is the tribe of Homininae that comprises Humans , and two species of the genus Pan (the Common Chimpanzee and the Bonobo), their ancestors, and the extinct lineages of their common ancestor. Members of the tribe are called hominins (cf. Hominidae, "hominids"). The subtribe Hominina is the "human" branch, including
Sahelanthropus tchadensis · Orrorin tugenensis Orrorin tugenensis is considered to be the second-oldest known hominin ancestor that is possibly related to modern humans, and it is the only species classified in genus Orrorin. The name was given by the discoverers who found Orrorin fossils in the Tugen Hills of Kenya. By using radiometric dating techniques, the volcanic tuffs and lavas, faunal · Ardipithecus Ardipithecus is a very early hominin genus. Two species are described in the literature: A. ramidus, which lived about 4.4 million years ago during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago · Kenyanthropus platyops Kenyanthropus platyops is a 3.5 to 3.2 million year old hominin fossil that was discovered in Lake Turkana, Kenya in 1999 by Justus Erus, who was part of Meave Leakey's team. Leaky (2001) proposes that the fossil represents an entirely new hominine genus, while others classify it as a separate species of Australopithecus, Australopithecus platyops,
Australopithecines The term australopithecine refers generally to any species in the related genera Australopithecus or Paranthropus. These species occurred in the Plio-Pleistocene era, and were bipedal and dentally similar to humans, but with a brain size not much larger than modern apes, lacking the encephalization characteristics of the genus Homo
Australopithecus Australopithecus is a genus of hominids that are now extinct. From the evidence gathered by palaeontologists and archaeologists, it appears that the Australopithecus genus evolved in eastern Africa around 4 million years ago before spreading throughout the continent and eventually becoming extinct 2 million years ago. During this time period,: A. anamensis Australopithecus anamensis is a stem-human species that lived approximately four million years ago. Nearly one hundred fossil specimens are known from Kenya and Ethiopia, representing over 20 individuals · A. afarensis Australopithecus afarensis is an extinct hominin which lived between 3.7 and 2.9 million years ago.[citation needed] A. afarensis was slenderly built, like the younger Australopithecus africanus. It is thought that A. afarensis was ancestral to both the genus Australopithecus and the genus Homo, which includes the modern human species, Homo · A. bahrelghazali Australopithecus bahrelghazali is a fossil hominin that was first discovered in 1993 by the paleontologist Michel Brunet in the Bahr el Ghazal valley near Koro Toro, in Chad, that Brunet named Abel. It was dated using Berylium based Radiometric dating as living circa. 3.6 million years ago · A. africanus Australopithecus africanus was an early hominid, an australopithecine, who lived between 2–3 million years ago in the Pliocene. In common with the older Australopithecus afarensis, A. africanus was slenderly built, or gracile, and was thought to have been a direct ancestor of modern humans. Fossil remains indicate that A. africanus was · A. garhi Australopithecus garhi is a gracile australopithecine species whose fossils were discovered in 1996 by a research team led by Ethiopian paleontologist Berhane Asfaw and Tim White, an American paleontologist. The hominin remains are believed to be a human ancestor species and the final missing link between the Australopithecus genus and the human · A. sediba Australopithecus sediba is a species of Australopithecus, based on fossil remains dated to 1.78 to 1.95 million years ago in the Pleistocene. The species is known from two partial skeletons discovered in the Malapa Fossil Site at the Cradle of Humankind World Heritage Site in South Africa, one a juvenile male, (the holotype), the other an adult Paranthropus The robust australopithecines, members of the extinct hominin genus Paranthropus , were bipedal hominids that probably descended from the gracile australopithecine hominids (Australopithecus): P. aethiopicus Paranthropus aethiopicus is an extinct species of hominid. The finding discovered in 1985 by Alan Walker in West Turkana, Kenya, KNM WT 17000 , is one of the earliest examples of robust pliocene hominids. The skull is dated to 2.5 million years ago, older than the later forms of robust australopithecines. Anthropologists suggest that P · P. boisei Paranthropus boisei was an early hominin and described as the largest of the Paranthropus species. It lived from about 2.6 until about 1.2 million years ago during the Pliocene and Pleistocene epochs in Eastern Africa · P. robustus Paranthropus robustus was originally discovered in Southern Africa in 1938. The development of P. robustus, namely in cranial features, seemed to be aimed in the direction of a "heavy-chewing complex". Because of the definitive traits that are associated with this robust line of australopithecine, anthropologist Robert Broom erected the
Humans and Proto-humans
Homo Homo is the genus that includes modern humans and species closely related to them. The genus is estimated to be about 2.3 to 2.4 million years old, evolving from australopithecine ancestors with the appearance of Homo habilis. Specifically, H. habilis is assumed to be the direct descendant of Australopithecus garhi which lived about 2.5 million: H. habilis Homo habilis is a species of the genus Homo, which lived from approximately 2.3 to 1.4 million years ago at the beginning of the Pleistocene period. The discovery and description of this species is credited to both Mary and Louis Leakey, who found fossils in Tanzania, East Africa, between 1962 and 1964. Homo habilis (or possibly H. rudolfensis) is · H. rudolfensis Homo rudolfensis is a fossil human species discovered by Bernard Ngeneo, a member of a team led by anthropologist Richard Leakey and zoologist Meave Leakey in 1972, at Koobi Fora on the east side of Lake Rudolf in Kenya. The scientific name Homo rudolfensis was proposed in 1986 by V. P. Alekseyev for the specimen Skull 1470 (KNM ER 1470). Skull 147 · H. gautengensis · H. georgicus Homo georgicus is a species of Homo that was suggested in 2002 to describe fossil skulls and jaws found in Dmanisi, Georgia in 1999 and 2001, which seem intermediate between Homo habilis and H. erectus. A partial skeleton was discovered in 2001. The fossils are about 1.8 million years old. The remains were first discovered in 1991 by Georgian · H. ergaster · H. erectus (H. e. lantianensis · H. e. palaeojavanicus · H. e. pekinensis · H. e. nankinensis · H. e. wushanensis · H. e. yuanmouensis · H. e. soloensis) · H. cepranensis · H. antecessor · H. heidelbergensis · Denisova hominin · H. neanderthalensis · H. rhodesiensis · H. floresiensis · Archaic Homo sapiens · Anatomically modern humans (H. s. idaltu · H. s. sapiens)
Topics: Timeline of human evolution · List of human evolution fossils · Human evolutionary genetics Models: Recent African origin · Multiregional origin

Categories: Hominina | Miocene mammals | Fossil taxa described in 2002

 

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